Håkon Dahle

• Rivera-Thorsen, T. Emil; Welch, Brian; Hutchison, Taylor; Hayes, Matthew J.; Rigby, Jane R. & Kim, Keunho [Vis alle 16 forfattere av denne artikkelen] (2026). The Sunburst Arc with JWST. IV. The Importance of Interaction, Turbulence, and Feedback for Lyman-continuum Escape. The Astrophysical Journal (ApJ). ISSN 0004-637X. 1000(2). doi: 10.3847/1538-4357/ae4c3a. Fulltekst i vitenarkiv Vis sammendrag

  At present, the best opportunity for detailed Lyman continuum (LyC) escape studies is in gravitationally lensed galaxies at z ≳ 2. Only one such galaxy currently exists in the literature with sufficient magnification and spatial resolution: the Sunburst Arc at redshift z = 2.37. Here, we present rest-frame optical JWST NIRSpec integral field observations of the Sunburst Arc that cover a large fraction of the source plane. From this dataset, we generate precise maps of interstellar medium (ISM) kinematics, dust geometry, ionization, and chemical enrichment. We extract a stacked spectrum of five gravitationally lensed images of the LyC leaking star cluster, as well as a μ−1 weighted, integrated spectrum of most of the galaxy, enabling a direct comparison to other LyC leakers in the literature. We find that the galaxy rotates but also shows strong, possibly dominant, signatures of turbulence, which are indicative of recent or ongoing major interaction. The cluster that leaks ionizing photons shows little difference from the rest of the galaxy in terms of kinematics or dust coverage, but dramatically elevated ionization, indicating that photoionization is the predominant mechanism that creates paths for LyC escape. We propose that tidal stripping of H I gas due to an interaction may have removed a large portion of the neutral ISM around the LyC emitting cluster, making it easier for the cluster to completely ionize the rest.

• Cloonan, Aidan P.; Khullar, Gourav; Napier, Kate A.; Gladders, Michael D.; Dahle, Håkon & Rosener, Riley [Vis alle 41 forfattere av denne artikkelen] (2025). COOL-LAMPS. VIII. Known Wide-separation Lensed Quasars and Their Host Galaxies Reveal a Lack of Evolution in M_BH/M⋆ Since z ∼ 3. The Astrophysical Journal (ApJ). ISSN 0004-637X. 987(2). doi: 10.3847/1538-4357/addabf. Fulltekst i vitenarkiv Vis sammendrag

  Wide-separation lensed quasars (WSLQs) are a rare class of strongly lensed quasars, magnified by foreground massive galaxy clusters, with typically large magnifications of the multiple quasar images. They are a relatively unexplored opportunity for detailed study of quasar host galaxies. The current small sample of known WSLQs has a median redshift of z  ≈ 2.1, larger than most other samples of quasar host galaxies studied to date. Here, we derive precise constraints on the properties of six WSLQs and their host galaxies, using parametric surface brightness fitting, measurements of quasar emission lines, and stellar population synthesis of host galaxies in six WSLQ systems. Our results, with significant uncertainty, indicate that these six hosts are a mixture of star-forming and quiescent galaxies. To probe for coevolution between active galactic nuclei (AGNs) and host galaxies, we model the offset from the local ( z = 0) M BH – M ⋆ relation as a simple power law in redshift. Accounting for selection effects, a WSLQ-based model for evolution in the M BH – M ⋆ relation has a power-law index of γ M  = −0.42 ± 0.31, consistent with no evolution. Compared to several literature samples, which mostly probe unlensed quasars at z  < 2, the WSLQ sample shows less evolution from the local relation, at ∼4 σ . We find that selection effects and choices of M BH calibration are the most important systematics in these comparisons. Given that we resolve host galaxy flux confidently even from the ground in some instances, our work demonstrates that WSLQs and highly magnified AGNs are exceptional systems for future AGN–host coevolution studies.

• Choe, S.; Rivera-Thorsen, T. Emil; Dahle, Håkon; Sharon, K.; Owens, M. Riley & Rigby, J. R. [Vis alle 14 forfattere av denne artikkelen] (2025). The Sunburst Arc with JWST: II. Observations of an Eta Carinae analog at z = 2.37. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 698. doi: 10.1051/0004-6361/202450685. Fulltekst i vitenarkiv Vis sammendrag

  Context. The peculiar object known as Godzilla resides within the gravitationally lensed Sunburst Arc at z  = 2.37. Despite being very bright, it appears in only one of the twelve lensed images of the source galaxy, exhibiting unusual spectroscopic properties that have not been found in any other clumps. Aims. We use JWST’s unique combination of spatial resolution and spectroscopic sensitivity to propose a unified, coherent explanation of the physical nature of Godzilla. Methods. We measured the fluxes and kinematic properties of rest-optical emission lines in Godzilla and its surrounding regions. Using standard line ratio-based diagnostic methods in combination with NIRCam imaging and ground based rest-UV spectra, we have characterized Godzilla and its surroundings. Results. Among the set of around 60 detected lines, we found a cascade of strong O  I lines pumped by intense Ly β emission, as well as Ly α -pumped rest-optical Fe  II lines, reminiscent of the Weigelt blobs in the local luminous blue variable (LBV) star Eta Carinae. The spectra and imagery of Godzilla and two faint adjacent images, along with the detection of a low-surface brightness foreground galaxy in the NIRCam data support the interpretation that Godzilla is an extremely magnified object, due to the alignment with lensing caustics. We find that Godzilla is part of a previously identified clump, comprising ∼10 − 25 % of it, with a magnification in the range of ≈600 − 25 000 (depending on the models and images used for comparison). The unique O  I source in Godzilla is aptly explained as a non-erupting LBV accompanied by a hotter companion and/or gas condensations exposed to more intense radiation, compared to the Weigelt blobs. If Godzilla is confirmed to contain an LBV star in future studies, this finding would expand the distance to the furthest known LBV from a dozen Mpc to several Gpc.

• Welch, Brian; Rivera-Thorsen, T. Emil; Rigby, Jane R.; Hutchison, Taylor A.; Olivier, Grace M. & Berg, Danielle A. [Vis alle 14 forfattere av denne artikkelen] (2025). The Sunburst Arc with JWST. III. An Abundance of Direct Chemical Abundances. The Astrophysical Journal (ApJ). ISSN 0004-637X. 980(1). doi: 10.3847/1538-4357/ada76c. Fulltekst i vitenarkiv Vis sammendrag

  We measure the gas-phase abundances of the elements He, N, O, Ne, S, Ar, and Fe in an individual H ii region known to be leaking Lyman-continuum photons in the Sunburst Arc, a highly magnified galaxy at redshift z = 2.37. We detect the temperature-sensitive auroral lines [S ii] λλ4070, 4076, [O iii] λ4363, [S iii] λ6314, [O ii] λλ7320, 7330, and [Ne iii] λ3343 in a stacked spectrum of five multiple images of the Lyman-continuum emitter (LCE), from which we directly measure the electron temperature in the low-, intermediate-, and high-ionization zones. We also detect the density-sensitive doublets of [O ii] λλ3727, 3730, [S ii] λλ6718, 6733, and [Ar iv] λλ4713, 4741, which constrain the density in both the low- and high-ionization gas. With these temperature and density measurements, we measure gas-phase abundances with similar rigor as studies of local galaxies and H ii regions. We measure a gas-phase metallicity for the LCE of 12 + (log(O/H) = 7,97 +-0.05, and find an enhanced nitrogen abundance log(N/O) = -0.65+0.16-0.25. This nitrogen abundance is consistent with enrichment from a population of Wolf–Rayet stars, additional signatures of which are reported in a companion paper. Abundances of sulfur, argon, neon, and iron are consistent with local low-metallicity H ii regions and low-redshift galaxies. This study represents the most complete chemical abundance analysis of an individual H ii region at Cosmic Noon to date, which enables direct comparisons between local H ii regions and those in the distant Universe.

• Mork, Simon D.; Gladders, Michael D.; Khullar, Gourav; Sharon, Keren; Chicoine, Nathalie & Cloonan, Aidan P. [Vis alle 30 forfattere av denne artikkelen] (2025). COOL-LAMPS. VII. Quantifying Strong-lens Scaling Relations with 177 Cluster-scale Strong Gravitational Lenses in DECaLS. The Astrophysical Journal (ApJ). ISSN 0004-637X. 979(2). doi: 10.3847/1538-4357/ada24c. Fulltekst i vitenarkiv Vis sammendrag

  We estimate the Einstein-radius-enclosed total mass for 177 cluster-scale strong gravitational lenses identified by the ChicagO Optically selected Lenses Located At the Margins of Public Surveys (COOL-LAMPS) collaboration with lens redshifts ranging from 0.2 ⪅ z ⪅ 1.0 using the brightest-cluster-galaxy (BCG) redshift and an observable proxy for the Einstein radius. We constrain the Einstein-radius-enclosed luminosity and stellar mass by fitting parametric spectral energy distributions to aperture photometry from the Dark Energy Camera Legacy Survey (DECaLS) in the g-, r-, and z-band Dark Energy Camera filters. We find that the BCG redshift, enclosed total mass, and enclosed luminosity are strongly correlated and well described by a planar relationship in 3D space. We find that the enclosed total mass and stellar mass are correlated with a logarithmic slope of 0.500 +0.029-0.031, and the enclosed total mass and stellar-to-total mass fraction are correlated with a logarithmic slope of -0.495+0.032-0.033. In tandem with the small radii within which these slopes are constrained, this may suggest invariance in baryon conversion efficiency and feedback strength as a function of cluster-centric radii in galaxy clusters. Additionally, the correlations described here should have utility in ranking strong-lensing candidates in upcoming imaging surveys—such as Rubin/Legacy Survey of Space and Time—in which an algorithmic treatment of strong lenses will be needed due to the sheer volume of data these surveys will produce.

• Rivera-Thorsen, Thøger Emil Juul; Chisholm, J.; Welch, B.; Rigby, J.R.; Hutchison, T. & Florian, M. [Vis alle 16 forfattere av denne artikkelen] (2024). The Sunburst Arc with JWST: I. Detection of Wolf-Rayet stars injecting nitrogen into a low-metallicity, z = 2.37 proto-globular cluster leaking ionizing photons. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 690. doi: 10.1051/0004-6361/202450359. Fulltekst i vitenarkiv Vis sammendrag

  We report the detection of a population of Wolf-Rayet (WR) stars in the Sunburst Arc, a strongly gravitationally lensed galaxy at redshift z = 2.37. As the brightest known lensed galaxy, the Sunburst Arc has become an important cosmic laboratory for studying star and cluster formation, Lyman α (Lyα) radiative transfer, and Lyman continuum (LyC) escape. Here, we present the first results of JWST/NIRSpec IFU observations of the Sunburst Arc, focusing on a stacked spectrum of the 12-fold imaged Sunburst LyC-emitting (LCE) cluster. In agreement with previous studies, we find that the Sunburst LCE cluster is a very massive, compact star cluster with Mdyn = (9 ± 1)×106 M⊙. Our age estimate of 4.2–4.5 Myr is much larger than the crossing time of tcross = 183 ± 9 kyr, indicating that the cluster is dynamically evolved and consistent with it being gravitationally bound. We find a significant nitrogen enhancement of the low ionization state interstellar medium (ISM), with log(N/O) =  − 0.74 ± 0.09, which is ≈0.8 dex above typical values for H II regions of a similar metallicity in the local Universe. We find broad stellar emission complexes around He IIλ4686 and C IVλ5808 with associated nitrogen emission; this is the first time WR signatures have been directly observed at redshifts above ∼0.5. The strength of the WR signatures cannot be reproduced by stellar population models that only include single-star evolution. While models with binary evolution better match the WR features, they still struggle to reproduce the nitrogen-enhanced WR features. JWST reveals the Sunburst LCE cluster to be a highly ionized proto-globular cluster with low oxygen abundance and extreme nitrogen enhancement that hosts a population of WR stars, likely including a previously suggested population of very massive stars (VMSs), which together are rapidly enriching the surrounding medium.

• Navarre, Alexander; Khullar, Gourav; Bayliss, Matthew B.; Dahle, Håkon; Florian, Michael & Gladders, Michael [Vis alle 13 forfattere av denne artikkelen] (2024). Resolving Clumpy versus Extended Lyα in Strongly Lensed, High-redshift Lyα Emitters. The Astrophysical Journal (ApJ). ISSN 0004-637X. 962(2). doi: 10.3847/1538-4357/ad10ad. Fulltekst i vitenarkiv Vis sammendrag

  We present six strongly gravitationally lensed Ly α emitters (LAEs) at z ∼ 4–5 with Hubble Space Telescope (HST) narrowband imaging isolating Lyα. Through complex radiative transfer Lyα encodes information about the spatial distribution and kinematics of the neutral hydrogen upon which it scatters. We investigate the galaxy properties and Ly α morphologies of our sample. Many previous studies of high-redshift LAEs have been limited in Lyα spatial resolution. In this work we take advantage of high-resolution Lyα imaging boosted by lensing magnification, allowing us to probe subgalactic scales that are otherwise inaccessible at these redshifts. We use broadband imaging from HST (rest-frame UV) and Spitzer (rest-frame optical) in spectral energy distribution fitting, providing estimates of the stellar masses (∼10 8–10 9M⊙), stellar population ages (t50 < 40 Myr), and amounts of dust (A V∼0.1–0.6, statistically consistent with zero). We employ nonparametric star formation histories to probe the young stellar populations which create the Lyα. We also examine the offsets between the Ly α and stellar continuum, finding small upper limits of offsets (<0.″1) consistent with studies of low-redshift LAEs, indicating our galaxies are not interacting or merging. Finally, we find a bimodality in our sample’s Ly α morphologies: clumpy and extended. We find a suggestive trend: our LAEs with clumpy Lyα are generally younger than the LAEs with extended Lyα , suggesting a possible correlation with age.

• Omoruyi, Osase; Tremblay, Grant R.; Combes, Francoise; Davis, Timothy A.; Gladders, Michael D. & Vikhlinin, Alexey [Vis alle 22 forfattere av denne artikkelen] (2024). Beads-on-a-string Star Formation Tied to One of the Most Powerful Active Galactic Nucleus Outbursts Observed in a Cool-core Galaxy Cluster. The Astrophysical Journal (ApJ). ISSN 0004-637X. 963(1). doi: 10.3847/1538-4357/ad1101. Fulltekst i vitenarkiv Vis sammendrag

  With two central galaxies engaged in a major merger and a remarkable chain of 19 young stellar superclusters wound around them in projection, the galaxy cluster SDSS J1531+3414 (z = 0.335) offers an excellent laboratory to study the interplay between mergers, active galactic nucleus (AGN) feedback, and star formation. New Chandra X-ray imaging reveals rapidly cooling hot (T ∼ 106 K) intracluster gas, with two wings forming a concave density discontinuity near the edge of the cool core. LOFAR 144 MHz observations uncover diffuse radio emission strikingly aligned with the wings, suggesting that the wings are actually the opening to a giant X-ray supercavity. The steep radio emission is likely an ancient relic of one of the most energetic AGN outbursts observed, with 4pV > 1061 erg. To the north of the supercavity, GMOS detects warm (T ∼ 104 K) ionized gas that enshrouds the stellar superclusters but is redshifted up to +800 km s−1 with respect to the southern central galaxy. The Atacama Large Millimeter/submillimeter Array detects a similarly redshifted ∼1010M⊙ reservoir of cold (T ∼ 102 K) molecular gas, but it is offset from the young stars by ∼1–3 kpc. We propose that the multiphase gas originated from low-entropy gas entrained by the X-ray supercavity, attribute the offset between the young stars and the molecular gas to turbulent intracluster gas motions, and suggest that tidal interactions stimulated the beads-on-a-string star formation morphology.

• Cathey, Jared; Gonzalez, Anthony H.; Lower, Sidney; Phadke, Kedar A.; Spilker, Justin & Aravena, Manuel [Vis alle 27 forfattere av denne artikkelen] (2024). TEMPLATES: Characterization of a Merger in the Dusty Lensing SPT0418-47 System. The Astrophysical Journal (ApJ). ISSN 0004-637X. 967(1). doi: 10.3847/1538-4357/ad33c9. Fulltekst i vitenarkiv
• Klein, Maxwell; Sharon, Keren; Napier, Kate; Gladders, Michael D.; Khullar, Gourav & Bayliss, Matthew [Vis alle 23 forfattere av denne artikkelen] (2024). COOL-LAMPS. VI. Lens Model and New Constraints on the Properties of COOL J1241+2219, a Bright z = 5 Lyman Break Galaxy and its z = 1 Cluster Lens. The Astrophysical Journal (ApJ). ISSN 0004-637X. 963(1). doi: 10.3847/1538-4357/ad22de. Fulltekst i vitenarkiv
• Welch, Brian; Olivier, Grace M.; Hutchison, Taylor A.; Rigby, Jane R.; Berg, Danielle A. & Aravena, Manuel [Vis alle 23 forfattere av denne artikkelen] (2024). TEMPLATES: Direct Abundance Constraints for Two Lensed Lyman-break Galaxies. The Astrophysical Journal (ApJ). ISSN 0004-637X. 975(2). doi: 10.3847/1538-4357/ad79ec. Fulltekst i vitenarkiv Vis sammendrag

  Using integrated spectra for two gravitationally lensed galaxies from the JWST TEMPLATES Early Release Science program, we analyze faint auroral lines, which provide direct measurements of the gas-phase chemical abundance. For the brighter galaxy, SGAS1723+34 (z = 1.3293), we detect the [O iii] λ4363, [S iii] λ6312, and [O ii] λλ7320, 7330 auroral emission lines, and set an upper limit for the [N ii] λ5755 line. For the second galaxy, SGAS1226+21 (z = 2.925), we do not detect any auroral lines, and report upper limits. With these measurements and upper limits, we constrain the electron temperatures in different ionization zones within both of these galaxies. For SGAS1723+34, where auroral lines are detected, we calculate direct oxygen and nitrogen abundances, finding an N/O ratio consistent with observations of nearby (z ∼ 0) galaxies. These observations highlight the potent combination of JWST and gravitational lensing to measure faint emission lines in individual distant galaxies and to directly study the chemical abundance patterns in those galaxies.

• Gassis, Raven; Bayliss, Matthew B.; Sharon, Keren; Mahler, Guillaume; Gladders, Michael D. & Dahle, Håkon [Vis alle 11 forfattere av denne artikkelen] (2024). Understanding shape and centroid deviations in 39 strong lensing galaxy clusters in various dynamical states. I Mayet, F.; Catalano, A.; Macías-Pérez, J.F. & Perotto, L. (Red.), mm Universe 2023 - Observing the Universe at mm Wavelengths. EDP Sciences. ISSN 9782759891252. doi: 10.1051/epjconf/202429300021. Fulltekst i vitenarkiv Vis sammendrag

  Through observational tests of strong lensing galaxy clusters, we can test simulation derived structure predictions that follow from Λ Cold Dark Matter (ΛCDM) cosmology. The shape and centroid deviations between the total matter distribution, stellar matter distributions, and hot intracluster gas distribution serve as an observational test of these theoretical structure predictions. We measure the position angles, ellipticities, and locations/centroids of the brightest cluster galaxy (BCG), intracluster light (ICL). the hot intracluster medium (ICM), and the core lensing mass for a sample of strong lensing galaxy clusters from the SDSS Giant Arcs Survey (SGAS). We utilize HST WFC3/1R imaging data to measure the shapes/centroids of the ICL and BCG distributions and use Chandra ACIS-I X-ray data to measure the shapes/centroids of the ICM. Additionally, we measure the concentration parameter (c) and asymmetry parameter (A) to incorporate cluster dynamical state into our analysis. Using this multicomponent approach, we evaluate the different components in terms of their ability to trace out the DM halo of clusters in various dynamical states.

• Jung, Intae; Ferguson, Henry C.; Hayes, Matthew J.; Henry, Alaina; Jaskot, Anne E. & Schaerer, Daniel [Vis alle 20 forfattere av denne artikkelen] (2024). Constraints on the Lyman Continuum Escape from Low-mass Lensed Galaxies at 1.3 ≤ z ≤ 3.0. The Astrophysical Journal (ApJ). ISSN 0004-637X. 971(2). doi: 10.3847/1538-4357/ad554d. Fulltekst i vitenarkiv Vis sammendrag

  Low-mass galaxies can significantly contribute to reionization due to their potentially high Lyman continuum (LyC) escape fraction and relatively high space density. We present a constraint on the LyC escape fraction from low-mass galaxies at z = 1.3–3.0. We obtained rest-frame UV continuum imaging with the ACS/SBC and the WFC3/UVIS from the Hubble Space Telescope for eight strongly lensed galaxies that were identified in the Sloan Giant Arc Survey and the Cluster Lensing and Supernova survey with Hubble. The targeted galaxies were selected to be spectroscopically confirmed, highly magnified, and blue in their UV spectral shapes (β < −1.7). Our targets include intrinsically low-luminosity galaxies down to a magnification-corrected absolute UV magnitude MUV ∼ −14. We perform custom-defined aperture photometry to place the most reliable upper limits of LyC escape from our sample. From our observations, we report no significant (>2σ) detections of LyC fluxes, placing 1σ upper limits on the absolute LyC escape fractions of 3%–15%. Our observations do not support the expected increased escape fractions of LyC photons from intrinsically UV faint sources. Considering the highly anisotropic geometry of LyC escape, increasing the sample size of faint galaxies in future LyC observations is crucial.

• Owens, M. Riley; Kim, Keunho J.; Bayliss, Matthew B.; Rivera-Thorsen, T. Emil; Sharon, Keren & Rigby, Jane R. [Vis alle 20 forfattere av denne artikkelen] (2024). Connecting Lyα and Ionizing Photon Escape in the Sunburst Arc. The Astrophysical Journal (ApJ). ISSN 0004-637X. 977(2). doi: 10.3847/1538-4357/ad9247. Fulltekst i vitenarkiv
• Napier, Kate; Gladders, Michael D.; Sharon, Keren; Dahle, Håkon; Cloonan, Aidan P. & Mahler, Guillaume [Vis alle 21 forfattere av denne artikkelen] (2023). COOL-LAMPS. Discovery of COOL J0335-1927, a Gravitationally Lensed Quasar at z=3.27 with an Image Separation of 23.3 arcsec. Astrophysical Journal Letters. ISSN 2041-8205. 954(2). doi: 10.3847/2041-8213/acf132. Fulltekst i vitenarkiv
• Shalyapin, Vyacheslav N.; Goicoechea, Luis J.; Dyrland, Karianne & Dahle, Håkon (2023). Andromeda’s Parachute: Time Delays and Hubble Constant. The Astrophysical Journal (ApJ). ISSN 0004-637X. 955(2). doi: 10.3847/1538-4357/acee7e. Fulltekst i vitenarkiv Vis sammendrag

  The gravitational lens system PS J0147+4630 (Andromeda’s Parachute) consists of four quasar images ABCD and a lensing galaxy. We obtained r -band light curves of ABCD in the 2017−2022 period from monitoring with two 2 m class telescopes. Applying state-of-the-art curve-shifting algorithms to these light curves led to measurements of time delays between images, and the three independent delays relative to image D are accurate enough to be used in cosmological studies (uncertainty of about 4%): Δ t AD = −170.5 ± 7.0, Δ t BD = −170.4 ± 6.0, and Δ t CD = −177.0 ± 6.5 days, where image D is trailing all the other images. Our finely sampled light curves and some additional fluxes in the years 2010−2013 also demonstrated the presence of significant microlensing variations. From the measured delays relative to image D and typical values of the external convergence, recent lens mass models yielded a Hubble constant that is in clear disagreement with currently accepted values around 70 km s −1 Mpc −1 . We discuss how to account for a standard value of the Hubble constant without invoking the presence of an extraordinary high external convergence.

• Kim, Keunho J.; Bayliss, Matthew B.; Rigby, Jane R.; Gladders, Michael D.; Chisholm, John & Sharon, Keren [Vis alle 16 forfattere av denne artikkelen] (2023). Small Region, Big Impact: Highly Anisotropic Lyman-continuum Escape from a Compact Starburst Region with Extreme Physical Properties. Astrophysical Journal Letters. ISSN 2041-8205. 955(1). doi: 10.3847/2041-8213/acf0c5. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Extreme, young stellar populations are considered to be the primary contributor to cosmic reionization. How the Lyman continuum (LyC) escapes these galaxies remains highly elusive, and it is challenging to observe this process in actual LyC emitters without resolving the relevant physical scales. We investigate the Sunburst Arc, a strongly lensed LyC emitter at z = 2.37 that reveals an exceptionally small-scale (tens of parsecs) region of high LyC escape. The small (&lt;100 pc) LyC-leaking region has extreme properties: a very blue UV slope ( β = −2.9 ± 0.1), a high ionization state ([O iii ] λ 5007/[O ii ] λ 3727 = 11 ± 3 and [O iii ] λ 5007/H β = 6.8 ± 0.4), strong oxygen emission (EW([O iii ]) = 1095 ± 40 Å), and a high Ly α escape fraction (0.3 ± 0.03), none of which are found in nonleaking regions of the galaxy. The leaking region’s UV slope is consistent with approximately “pure” stellar light that is minimally contaminated by the surrounding nebular continuum emission or extinguished by dust. These results suggest a highly anisotropic LyC escape process such that LyC is produced and escapes from a small, extreme starburst region where the stellar feedback from an ionizing star cluster creates one or more “pencil-beam” channels in the surrounding gas through which LyC can directly escape. Such anisotropic escape processes imply that random sight-line effects drive the significant scatters between measurements of galaxy properties and LyC escape fraction, and that strong lensing is a critical tool for resolving the processes that regulate the ionizing budget of galaxies for reionization.

• Zhang, Yunchong; Manwadkar, Viraj; Gladders, Michael D.; Khullar, Gourav; Dahle, Håkon & Napier, Kate A. [Vis alle 24 forfattere av denne artikkelen] (2023). COOL-LAMPS. IV. A Sample of Bright Strongly Lensed Galaxies at 3 < z < 4. The Astrophysical Journal (ApJ). ISSN 0004-637X. 950(1). doi: 10.3847/1538-4357/acc9be. Fulltekst i vitenarkiv
• Martinez, Michael N.; Napier, Kate A.; Cloonan, Aidan P.; Sukay, Ezra; Gozman, Katya & Merz, Kaiya [Vis alle 19 forfattere av denne artikkelen] (2023). COOL-LAMPS. III. Discovery of a 25.9 arcsec Separation Quasar Lensed by a Merging Galaxy Cluster. The Astrophysical Journal (ApJ). ISSN 0004-637X. 946(2). doi: 10.3847/1538-4357/acbe39. Fulltekst i vitenarkiv
• Napier, Kate; Sharon, Keren; Dahle, Håkon; Bayliss, Matthew; Gladders, Michael D. & Mahler, Guillaume [Vis alle 8 forfattere av denne artikkelen] (2023). Hubble Constant Measurement from Three Large-separation Quasars Strongly Lensed by Galaxy Clusters. The Astrophysical Journal (ApJ). ISSN 0004-637X. 959(2). doi: 10.3847/1538-4357/ad045a. Fulltekst i vitenarkiv Vis sammendrag

  Tension between cosmic microwave background–based and distance ladder–based determinations of the Hubble constant H0 motivates the pursuit of independent methods that are not subject to the same systematic effects. A promising alternative, proposed by Refsdal in 1964, relies on the inverse scaling of H0 with the delay between the arrival times of at least two images of a strongly lensed variable source such as a quasar. To date, Refsdal's method has mostly been applied to quasars lensed by individual galaxies rather than by galaxy clusters. Using the three quasars strongly lensed by galaxy clusters (SDSS J1004+4112, SDSS J1029+2623, and SDSS J2222+2745) that have both multiband Hubble Space Telescope data and published time delay measurements, we derive H0, accounting for the systematic and statistical sources of uncertainty. While a single time delay measurement does not yield a well-constrained H0 value, analyzing the systems together tightens the constraint. Combining the six time delays measured in the three cluster-lensed quasars gives H0 = 74.1 ± 8.0 km s−1 Mpc−1. To reach 1% uncertainty in H0, we estimate that a sample size of order of 620 time delay measurements of similar quality as those from SDSS J1004+4112, SDSS J1029+2623, and SDSS J2222+2745 would be needed. Improving the lens modeling uncertainties by a factor of two and a half may reduce the needed sample size to 100 time delays, potentially reachable in the next decade.

• Spilker, Justin S.; Phadke, Kedar A.; Aravena, Manuel; Archipley, Melanie; Bayliss, Matthew B. & Birkin, Jack E. [Vis alle 39 forfattere av denne artikkelen] (2023). Spatial variations in aromatic hydrocarbon emission in a dust-rich galaxy. Nature. ISSN 0028-0836. 618(7966), s. 708–711. doi: 10.1038/s41586-023-05998-6. Fulltekst i vitenarkiv
• Mainali, Ramesh; Rigby, Jane R.; Chisholm, John; Bayliss, Matthew; Bordoloi, Rongmon & Gladders, Michael D. [Vis alle 16 forfattere av denne artikkelen] (2022). The Connection Between Galactic Outflows and the Escape of Ionizing Photons. The Astrophysical Journal (ApJ). ISSN 0004-637X. 940(2). doi: 10.3847/1538-4357/ac9cd6. Fulltekst i vitenarkiv Vis sammendrag

  Abstract We analyze spectra of a gravitationally lensed galaxy, known as the Sunburst Arc, that is leaking ionizing photons, also known as the Lyman continuum (LyC). Magnification from gravitational lensing permits the galaxy to be spatially resolved into one region that leaks ionizing photons and several that do not. Rest-frame UV and optical spectra from Magellan target 10 different regions along the lensed Arc, including six multiple images of the LyC leaking region and four regions that do not show LyC emission. The rest-frame optical spectra of the ionizing photon emitting regions reveal a blueshifted (Δ V = 27 km s −1 ) broad emission component (FWHM = 327 km s −1 ), comprising 55% of the total [O iii ] line flux, in addition to a narrow component (FWHM = 112 km s −1 ), suggesting the presence of strong highly ionized gas outflows. This is consistent with the high-velocity ionized outflow inferred from the rest-frame UV spectra. In contrast, the broad emission component is less prominent in the nonleaking regions, comprising ∼26% of total [O iii ] line flux. The high-ionization absorption lines are prominent in both the leaker and the nonleaker, but the low-ionization absorption lines are very weak in the leaker, suggesting that the line-of-sight gas is highly ionized in the leaker. Analyses of stellar wind features reveal that the stellar population of the LyC leaking regions is considerably younger (∼3 Myr) than that of the nonleaking regions (∼12 Myr), emphasizing that stellar feedback from young stars may play an important role in ionizing photon escape.

• Sharon, Keren; Mahler, Guillaume; Rivera-Thorsen, T. Emil; Dahle, Håkon; Gladders, Michael D. & Bayliss, Matthew B. [Vis alle 15 forfattere av denne artikkelen] (2022). The Cosmic Telescope That Lenses the Sunburst Arc, PSZ1 G311.65-18.48: Strong Gravitational Lensing Model and Source Plane Analysis. The Astrophysical Journal (ApJ). ISSN 0004-637X. 941(2). doi: 10.3847/1538-4357/ac927a. Fulltekst i vitenarkiv Vis sammendrag

  We present a strong-lensing analysis of the cluster PSZ1 G311.65−18.48, based on Hubble Space Telescope imaging, archival VLT/MUSE spectroscopy, and Chandra X-ray data. This cool-core cluster (z = 0.443) lenses the brightest lensed galaxy known, dubbed the "Sunburst Arc" (z = 2.3703), a Lyman continuum (LyC) emitting galaxy multiply imaged 12 times. We identify in this field 14 additional strongly lensed galaxies to constrain a strong-lens model and report secure spectroscopic redshifts of four of them. We measure a projected cluster core mass of M(<250 kpc) = {2.93}_{-0.02}^{+0.01}\times {10}^{14}$M⊙. The two least magnified but complete images of the Sunburst Arc's source galaxy are magnified by ∼13×, while the LyC clump is magnified by ∼4–80×. We present time delay predictions and conclusive evidence that a discrepant clump in the Sunburst Arc, previously claimed to be a transient, is not variable, thus strengthening the hypothesis that it results from an exceptionally high magnification. A source plane reconstruction and analysis of the Sunburst Arc finds its physical size to be 1 × 2 kpc and that it is resolved in three distinct directions in the source plane, 0°, 40°, and 75° (east of north). We place an upper limit of r ≲ 50 pc on the source plane size of unresolved clumps and r ≲ 32 pc for the LyC clump. Finally, we report that the Sunburst Arc is likely in a system of two or more galaxies separated by ≲6 kpc in projection. Their interaction may drive star formation and could play a role in the mechanism responsible for the leaking LyC radiation.

• Sukay, Ezra; Khullar, Gourav; Gladders, Michael D.; Sharon, Keren; Mahler, Guillaume & Napier, Kate [Vis alle 20 forfattere av denne artikkelen] (2022). COOL-LAMPS. II. Characterizing the Size and Star Formation History of a Bright Strongly Lensed Early-type Galaxy at Redshift 1.02. The Astrophysical Journal (ApJ). ISSN 0004-637X. 940(1). doi: 10.3847/1538-4357/ac9974. Fulltekst i vitenarkiv Vis sammendrag

  We present COOL J1323+0343, an early-type galaxy at z = 1.0153 ± 0.0006, strongly lensed by a cluster of galaxies at z = 0.353 ± 0.001. This object was originally imaged by DECaLS and noted as a gravitational lens by COOL-LAMPS, a collaboration initiated to find strong-lensing systems in recent public optical imaging data, and confirmed with follow-up data. With ground-based grzH imaging and optical spectroscopy from the Las Campanas Observatory and the Nordic Optical Telescope, we derive a stellar mass, metallicity, and star formation history from stellar-population synthesis modeling. The lens modeling implies a total magnification, summed over the three images in the arc, of μ ∼ 113. The stellar mass in the source plane is M* ∼ 10.64 M⊙ and the 1σ upper limit on the star formation rate (SFR) in the source plane is SFR ∼ 3.75 × 10−2 M⊙ yr−1 (log sSFR = −12.1 yr−1) in the youngest two age bins (0–100 Myr), closest to the epoch of observation. Our measurements place COOL J1323+0343 below the characteristic mass of the stellar mass function, making it an especially compelling target that could help clarify how intermediate-mass quiescent galaxies evolve. We reconstruct COOL J1323+0343 in the source plane and fit its light profile. This object is below the expected size evolution of an early-type galaxy at this mass with an effective radius re ∼ 0.5 kpc. This extraordinarily magnified and bright lensed early-type galaxy offers an exciting opportunity to study the morphology and star formation history of an intermediate-mass early-type galaxy in detail at z ∼ 1.

• Williams, Peter R.; Treu, Tommaso; Dahle, Håkon; Valenti, Stefano; Abramson, Louis & Barth, Aaron J. [Vis alle 10 forfattere av denne artikkelen] (2021). The Black Hole Mass of the z = 2.805 Multiply Imaged Quasar SDSS J2222+2745 from Velocity-resolved Time Lags of the C iv Emission Line. The Astrophysical Journal (ApJ). ISSN 0004-637X. 911(1). doi: 10.3847/1538-4357/abe943. Fulltekst i vitenarkiv
• Solimano, M.; González-López, J.; Barrientos, L.F.; Aravena, M.; López, S. & Tejos, N. [Vis alle 12 forfattere av denne artikkelen] (2021). Molecular gas budget and characterization of intermediate-mass star-forming galaxies at z ≈ 2-3. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 655. doi: 10.1051/0004-6361/202141835. Fulltekst i vitenarkiv Vis sammendrag

  Star-forming galaxies (SFGs) with stellar masses below 10 10   M ⊙ make up the bulk of the galaxy population at z  &gt; 2. The properties of the cold gas in these galaxies can only be probed in very deep observations or by targeting strongly lensed galaxies. Here we report the results of a pilot survey using the Atacama Compact Array of molecular gas in the most strongly magnified galaxies selected as giant arcs in optical data. The selection in rest-frame ultraviolet (UV) wavelengths ensures that sources are regular SFGs, without a priori indications of intense dusty starburst activity. We conducted Band 4 and Band 7 observations to detect mid- J CO, [C  I ] and thermal continuum as molecular gas tracers from four strongly lensed systems at z  ≈ 2 − 3: our targets are SGAS J1226651.3+215220 (A and B), SGAS J003341.5+024217 and the Sunburst Arc. The measured molecular mass was then projected onto the source plane with detailed lens models developed from high resolution Hubble Space Telescope observations. Multiwavelength photometry was then used to obtain the intrinsic stellar mass and star formation rate via spectral energy distribution modeling. In only one of the sources are the three tracers robustly detected, while in the others they are either undetected or detected in continuum only. The implied molecular gass masses range from 4 × 10 9   M ⊙ in the detected source to an upper limit of ≲10 9   M ⊙ in the most magnified source. The inferred gas fraction and gas depletion timescale are found to lie approximately 0.5–1.0 dex below the established scaling relations based on previous studies of unlensed massive galaxies, but in relative agreement with existing literature about UV-bright lensed galaxies at these high redshifts. Our results indicate that the cold gas content of intermediate to low mass galaxies should not be extrapolated from the trends seen in more massive high- z galaxies. The apparent gas deficit is robust against biases in the stellar mass or star formation rate. However, we find that in this mass-metallicity range, the molecular gas mass measurements are severely limited by uncertainties in the current tracer-to-gas calibrations.

• Khullar, Gourav; Gozman, Katya; Lin, Jason J.; Martinez, Michael N.; Acuña, Owen S. Matthews & Medina, Elisabeth [Vis alle 22 forfattere av denne artikkelen] (2021). COOL-LAMPS. I. An Extraordinarily Bright Lensed Galaxy at Redshift 5.04. The Astrophysical Journal (ApJ). ISSN 0004-637X. 906(2). doi: 10.3847/1538-4357/abcb86. Fulltekst i vitenarkiv
• Williams, Peter R.; Treu, Tommaso; Dahle, Håkon; Valenti, Stefano; Abramson, Louis & Barth, Aaron J. [Vis alle 11 forfattere av denne artikkelen] (2021). Dynamical Modeling of the C iv Broad Line Region of the z = 2.805 Multiply Imaged Quasar SDSS J2222+2745. Astrophysical Journal Letters. ISSN 2041-8205. 915(1). doi: 10.3847/2041-8213/ac081b. Fulltekst i vitenarkiv
• Rigby, J. R.; Florian, Michael K.; Acharyya, A.; Bayliss, M. B.; Gladders, M. D. & Sharon, K. [Vis alle 16 forfattere av denne artikkelen] (2021). A Comparison of Rest-frame Ultraviolet and Optical Emission-line Diagnostics in the Lensed Galaxy SDSS J1723+3411 at Redshift z = 1.3293. The Astrophysical Journal (ApJ). ISSN 0004-637X. 908(2). doi: 10.3847/1538-4357/abcfc9. Fulltekst i vitenarkiv
• Somboonpanyakul, Taweewat; McDonald, Michael; Bayliss, M. B.; Voit, Mark; Donahue, Megan & Gaspari, Massimo [Vis alle 9 forfattere av denne artikkelen] (2021). The Clusters Hiding in Plain Sight (CHiPS) Survey: CHIPS1911+4455, a Rapidly Cooling Core in a Merging Cluster. Astrophysical Journal Letters. ISSN 2041-8205. 907(1), s. 1–6. doi: 10.3847/2041-8213/abd540. Fulltekst i vitenarkiv
• Florian, Michael K.; Rigby, Jane R.; Acharyya, Ayan; Sharon, Keren; Gladders, Michael D. & Kewley, Lisa [Vis alle 17 forfattere av denne artikkelen] (2021). Spatial Variation in Strong Line Ratios and Physical Conditions in Two Strongly Lensed Galaxies at z ∼ 1.4. The Astrophysical Journal (ApJ). ISSN 0004-637X. 916(1). doi: 10.3847/1538-4357/ac0257. Fulltekst i vitenarkiv
• Barrena, R.; Ferragamo, A.; Rubiño-Martín, J. A.; Streblyanska, A.; Aguado-Barahona, A. & Tramonte, D. [Vis alle 21 forfattere av denne artikkelen] (2020). Optical validation and characterisation of Planck PSZ1 sources at the Canary Islands observatories: II. Second year of ITP13 observations. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 638. doi: 10.1051/0004-6361/202037552. Fulltekst i vitenarkiv Vis sammendrag

  We report new galaxy clusters previously unknown included in the first Planck Sunyaev–Zeldovich (SZ) sources catalogue, the PSZ1. The results presented here were achieved during the second year of a two-year observational programme, the ITP13, developed at the Roque de los Muchachos Observatory (La Palma, Spain). Using the 2.5 m Isaac Newton telescope, the 3.5 m Telescopio Nazionale Galileo, the 4.2 m William Herschel telescope and the 10.4 m Gran Telescopio Canarias we characterised 75 SZ sources with low SZ significance, SZ S &lt;  5.32. We performed deep optical imaging and spectroscopy in order to associate actual galaxy clusters with the SZ Planck source. We adopted robust criteria, based on the 2D spatial distribution, richness, and velocity dispersions to confirm actual optical counterparts up to z &lt;  0.85. The selected systems are confirmed only if they are well aligned with respect to the PSZ1 coordinate and show high richness and high velocity dispersion. In addition, we also inspected the Compton y-maps and SZ significance in order to identify unrealistic detections. Following this procedure, we identify 26 cluster counterparts associated with the SZ emission, which means that only about 35% of the clusters considered in this low S/N PSZ1 subsample are validated. Forty-nine SZ sources (∼65% of this PSZ1 subset) remain unconfirmed. At the end of the ITP13 observational programme, we have studied 256 SZ sources with Dec ≥ −15° (212 of them completely unknown), finding optical counterparts for 152 SZ sources. The ITP13 validation programme has allowed us to update the PSZ1 purity, which is now more refined, increasing from 72% to 83% in the low SZ S/N regime. Our results are consistent with the predicted purity curve for the full PSZ1 catalogue and with the expected fraction of false detections caused by the non-Gaussian noise of foreground signals. We find a strong correlation between the number of unconfirmed sources and the thermal emission of diffuse galactic dust at 857 GHz, thus increasing the fraction of false Planck SZ detections at low galactic latitudes.

• Sharon, Keren; Bayliss, Matthew B.; Dahle, Håkon; Dunham, Samuel J.; Florian, Michael K. & Gladders, Michael D. [Vis alle 16 forfattere av denne artikkelen] (2020). Strong Lens Models for 37 Clusters of Galaxies from the SDSS Giant Arcs Survey. Astrophysical Journal Supplement Series. ISSN 0067-0049. 247(1). doi: 10.3847/1538-4365/ab5f13. Fulltekst i vitenarkiv Vis sammendrag

  We present strong gravitational lensing models for 37 galaxy clusters from the Sloan Digital Sky Survey Giant Arcs Survey. We combine data from multi-band Hubble Space Telescope Wide Field Camera 3 (WFC3) imaging, with ground-based imaging and spectroscopy from Magellan, Gemini, Apache Point Observatory, and the Multiple Mirror Telescope, in order to detect and spectroscopically confirm new multiply imaged lensed background sources behind the clusters. We report spectroscopic or photometric redshifts of sources in these fields, including cluster galaxies and background sources. Based on all available lensing evidence, we construct and present strong-lensing mass models for these galaxy clusters. The clusters span a redshift range of 0.176 < z < 0.66 with a median redshift of z = 0.45, and sample a wide range of dynamical masses, 1.5 < M 200 < 35 × 1014 ${M}_{\odot }$, as estimated from their velocity dispersions. As these clusters were selected as lenses primarily owing to a fortuitous alignment with background galaxies that results in giant arcs, they exhibit a wide range in Einstein radii, 1farcs3 < θ E < 23farcs1 for a source at z = 2, with a median θ E = 10farcs8. The reduced HST images and lens model outputs are made available to the scientific community as high-level data products with this publication.

• Fischer, Travis C.; Rigby, J. R.; Mahler, G.; Gladders, M.; Sharon, K. & Florian, M. [Vis alle 14 forfattere av denne artikkelen] (2019). Spatially Resolved Outflows in a Seyfert Galaxy at z = 2.39. The Astrophysical Journal (ApJ). ISSN 0004-637X. 875(2). doi: 10.3847/1538-4357/ab11c3. Fulltekst i vitenarkiv Vis sammendrag

  We present the first spatially resolved analysis of rest-frame optical and UV imaging and spectroscopy for a lensed galaxy at z = 2.39 hosting a Seyfert active galactic nucleus (AGN). Proximity to a natural guide star has enabled observations with high signal-to-noise ratio using Very Large Telescope SINFONI + adaptive optics (AO) of rest-frame optical diagnostic emission lines, which exhibit an underlying broad component with full width at half maximum ~ 700 km s−1 in both the Balmer and forbidden lines. Measured line ratios place the outflow robustly in the region of the ionization diagnostic diagrams associated with AGNs. This unique opportunity—combining gravitational lensing, AO guiding, redshift, and AGN activity—allows for a magnified view of two main tracers of the physical conditions and structure of the interstellar medium in a star-forming galaxy hosting a weak AGN at Cosmic Noon. By analyzing the spatial extent and morphology of the Lyα and dust-corrected Hα emission, disentangling the effects of star formation and AGN ionization on each tracer, and comparing the AGN-induced mass outflow rate to the host star formation rate, we find that the AGN does not significantly impact the star formation within its host galaxy.

• Lopez, S.; Tejos, N.; Barrientos, L. F.; Ledoux, C.; Sharon, Keren & Katsianis, A. [Vis alle 16 forfattere av denne artikkelen] (2019). Slicing the cool circumgalactic medium along the major axis of a star-forming galaxy at z = 0.7. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 491(3), s. 4442–4461. doi: 10.1093/mnras/stz3183. Fulltekst i vitenarkiv Vis sammendrag

  We present spatially resolved Echelle spectroscopy of an intervening Mg II–Fe II–Mg I absorption-line system detected at zabs = 0.73379 towards the giant gravitational arc PSZ1 G311.65–18.48. The absorbing gas is associated with an inclined disc-like star-forming galaxy, whose major axis is aligned with the two arc-segments reported here. We probe in absorption the galaxy’s extended disc continuously, at ≈3 kpc sampling, from its inner region out to 15× the optical radius. We detect strong (⁠W27960>0.3Å) coherent absorption along 13 independent positions at impact parameters D = 0–29 kpc on one side of the galaxy, and no absorption at D = 28–57 kpc on the opposite side (all de-lensed distances at zabs). We show that (1) the gas distribution is anisotropic; (2) W27960⁠, W26000⁠, W28520⁠, and the ratio W26000/W27960⁠, all anticorrelate with D; (3) the W27960–D relation is not cuspy and exhibits significantly less scatter than the quasar-absorber statistics; (4) the absorbing gas is co-rotating with the galaxy out to D ≲ 20 kpc, resembling a ‘flat’ rotation curve, but at D ≳ 20 kpc velocities decline below the expectations from a 3D disc-model extrapolated from the nebular [O II] emission. These signatures constitute unambiguous evidence for rotating extra-planar diffuse gas, possibly also undergoing enriched accretion at its edge. Arguably, we are witnessing some of the long-sought processes of the baryon cycle in a single distant galaxy expected to be representative of such phenomena.

• Rivera-Thorsen, Thøger Emil Juul; Dahle, Håkon; Chisholm, John; Florian, Michael K.; Gronke, Max Balthasar & Rigby, Jane R. [Vis alle 10 forfattere av denne artikkelen] (2019). Gravitational lensing reveals ionizing ultraviolet photons escaping from a distant galaxy. Science. ISSN 0036-8075. 366(6466), s. 738–741. doi: 10.1126/science.aaw0978. Fulltekst i vitenarkiv Vis sammendrag

  During the epoch of reionization, neutral gas in the early Universe was ionized by hard ultraviolet radiation emitted by young stars in the first galaxies. To do so, ionizing ultraviolet photons must escape from the host galaxy. We present Hubble Space Telescope observations of the gravitationally lensed post-reionization galaxy PSZ1-ARC G311.6602–18.4624 (nicknamed the “Sunburst Arc”), revealing bright, multiply imaged ionizing photon escape from a compact star-forming region through a narrow channel in an optically thick gas. The gravitational lensing magnification shows how ionizing photons escape this galaxy, contributing to the reionization of the Universe. The multiple sight lines to the source probe absorption by intergalactic neutral hydrogen on a scale of less than a few hundred parsecs.

• Chisholm, J.; Rigby, J. R.; Bayliss, M.; Berg, D. A.; Dahle, Håkon & Gladders, M. [Vis alle 7 forfattere av denne artikkelen] (2019). Constraining the Metallicities, Ages, Star Formation Histories, and Ionizing Continua of Extragalactic Massive Star Populations. The Astrophysical Journal (ApJ). ISSN 0004-637X. 882(2). doi: 10.3847/1538-4357/ab3104. Fulltekst i vitenarkiv Vis sammendrag

  We infer the properties of massive star populations using the far-ultraviolet stellar continua of 61 star-forming galaxies: 42 at low redshift observed with the Hubble Space Telescope and 19 at z ~ 2 from the MegaSaura sample. We fit each stellar continuum with a linear combination of up to 50 single-age and single-metallicity starburst99 models. From these fits, we derive light-weighted ages and metallicities, which agree with stellar wind and photospheric spectral features, and infer the spectral shapes and strengths of the ionizing continua. Inferred light-weighted stellar metallicities span 0.05–1.5 Z ⊙ and are similar to the measured nebular metallicities. We quantify the ionizing continua using the ratio of the ionizing flux at 900 Å to the non-ionizing flux at 1500 Å and demonstrate the evolution of this ratio with stellar age and metallicity using theoretical single-burst models. These single-burst models only match the inferred ionizing continua of half of the sample, while the other half are described by a mixture of stellar ages. Mixed-age populations produce stronger and harder ionizing spectra than continuous star formation histories, but, contrary to previous studies that assume constant star formation, have similar stellar and nebular metallicities. Stellar population age and metallicity affect the far-UV continua in different and distinguishable ways; assuming a constant star formation history diminishes the diagnostic power. Finally, we provide simple prescriptions to determine the ionizing photon production efficiency (ξ ion) from the stellar population properties. The ξ ion inferred from the observed star-forming galaxies has a range of log(ξ ion) = 24.4–25.7 Hz erg−1 that depends on the stellar population age, metallicity, star formation history, and contributions from binary star evolution. These stellar population properties must be observationally determined to accurately determine the number of ionizing photons generated by massive stars.

• Bayliss, Matthew B.; McDonald, M.; Sharon, Keren; Gladders, Michael D.; Florian, M. & Chisholm, J. [Vis alle 22 forfattere av denne artikkelen] (2019). An X-ray detection of star formation in a highly magnified giant arc. Nature Astronomy. 4, s. 159–166. doi: 10.1038/s41550-019-0888-7. Fulltekst i vitenarkiv
• Dunham, Samuel J.; Sharon, Keren; Florian, Michael K.; Rigby, Jane R.; Gladders, Michael D. & Bayliss, Matthew B. [Vis alle 11 forfattere av denne artikkelen] (2019). Lens Model and Source Reconstruction Reveal the Morphology and Star Formation Distribution in the Cool Spiral LIRG SGAS J143845.1+145407. The Astrophysical Journal (ApJ). ISSN 0004-637X. 875(1). doi: 10.3847/1538-4357/ab0d7d. Fulltekst i vitenarkiv Vis sammendrag

  We present Hubble Space Telescope (HST) imaging and grism spectroscopy of a strongly lensed LIRG at z = 0.816, SGAS 143845.1+145407, and use the magnification boost of gravitational lensing to study the distribution of star formation throughout this galaxy. Based on the HST imaging data, we create a lens model for this system; we compute the mass distribution and magnification map of the z = 0.237 foreground lens. We find that the magnification of the lensed galaxy ranges between 2 and 10, with a total magnification (measured over all the images of the source) of μ = ${11.8}_{-2.4}^{+4.6}$. We find that the total projected mass density within ~34 kpc of the brightest cluster galaxy is ${6.0}_{-0.7}^{+0.3}\times {10}^{12}$ ${M}_{\odot }$. Using the lens model we create a source reconstruction for SGAS 143845.1+145407, which, paired with a faint detection of Hα in the grism spectroscopy, allows us to finally comment directly on the distribution of star formation in a z ~ 1 LIRG. We find widespread star formation across this galaxy, in agreement with the current understanding of these objects. However, we note a deficit of Hα emission in the nucleus of SGAS 143845.1+145407, likely due to dust extinction.

• Barrena, R.; Streblyanska, A.; Ferragamo, A.; Rubiño-Martín, J. A.; Aguado-Barahona, A. & Tramonte, D. [Vis alle 23 forfattere av denne artikkelen] (2018). Optical validation and characterization of Planck PSZ1 sources at the Canary Islands observatories: I. First year of ITP13 observations. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 616. doi: 10.1051/0004-6361/201732315. Fulltekst i vitenarkiv Vis sammendrag

  We have identified new clusters and characterized previously unknown Planck Sunyaev–Zeldovich (SZ) sources from the first Planck catalogue of SZ sources (PSZ1). The results presented here correspond to an optical follow-up observational programme developed during approximately one year (2014) at Roque de los Muchachos Observatory, using the 2.5 m Isaac Newton telescope, the 3.5 m Telescopio Nazionale Galileo, the 4.2 m William Herschel telescope and the 10.4 m Gran Telescopio Canarias. We have characterized 115 new PSZ1 sources using deep optical imaging and spectroscopy. We adopted robust criteria in order to consolidate the SZ counterparts by analysing the optical richness, the 2D galaxy distribution, and velocity dispersions of clusters. Confirmed counterparts are considered to be validated if they are rich structures, well aligned with the Planck PSZ1 coordinate and show relatively high velocity dispersion. Following this classification, we confirm 53 clusters, which means that 46% of this PSZ1 subsample has been validated and characterized with this technique. Sixty-two SZ sources (54% of this PSZ1 subset) remain unconfirmed. In addition, we find that the fraction of unconfirmed clusters close to the galactic plane (at |b| < 25°) is greater than that at higher galactic latitudes (|b| > 25°), which indicates contamination produced by radio emission of galactic dust and gas clouds on these SZ detections. In fact, in the majority of the cases, we detect important galactic cirrus in the optical images, mainly in the SZ target located at low galactic latitudes, which supports this hypothesis.

• Rigby, J. R.; Bayliss, M. B.; Chisholm, J.; Bordoloi, Rongmon; Sharon, K. & Gladders, M. D. [Vis alle 11 forfattere av denne artikkelen] (2018). The Magellan Evolution of Galaxies Spectroscopic and Ultraviolet Reference Atlas (MegaSaura). II. Stacked Spectra. The Astrophysical Journal (ApJ). ISSN 0004-637X. 853(1). doi: 10.3847/1538-4357/aaa2fc. Fulltekst i vitenarkiv Vis sammendrag

  We stack the rest-frame ultraviolet spectra of N = 14 highly magnified gravitationally lensed galaxies at redshifts $1.6\lt z\lt 3.6$. The resulting new composite spans $900\lt {\lambda }_{\mathrm{rest}}\lt 3000$ Å, with a peak signal-to-noise ratio (S/N) of 103 per spectral resolution element (~100 km s−1). It is the highest S/N, highest spectral resolution composite spectrum of z ~ 2–3 galaxies yet published. The composite reveals numerous weak nebular emission lines and stellar photospheric absorption lines that can serve as new physical diagnostics, particularly at high redshift with the James Webb Space Telescope (JWST). We report equivalent widths to aid in proposing for and interpreting JWST spectra. We examine the velocity profiles of strong absorption features in the composite, and in a matched composite of $z\sim 0$ COS/HST galaxy spectra. We find remarkable similarity in the velocity profiles at $z\sim 0$ and $z\sim 2$, suggesting that similar physical processes control the outflows across cosmic time. While the maximum outflow velocity depends strongly on ionization potential, the absorption-weighted mean velocity does not. As such, the bulk of the high-ionization absorption traces the low-ionization gas, with an additional blueshifted absorption tail extending to at least −2000 km s−1. We interpret this tail as arising from the stellar wind and photospheres of massive stars. Starburst99 models are able to replicate this high-velocity absorption tail. However, these theoretical models poorly reproduce several of the photospheric absorption features, indicating that improvements are needed to match observational constraints on the massive stellar content of star-forming galaxies at $z\sim 2$. We publicly release our composite spectra.

• Chisholm, John; Gazagnes, S; Schaerer, Daniel; Verhamme, Anne; Rigby, Jane R. & Bayliss, Matthew B. [Vis alle 9 forfattere av denne artikkelen] (2018). Accurately predicting the escape fraction of ionizing photons using rest-frame ultraviolet absorption lines. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 616. doi: 10.1051/0004-6361/201832758. Fulltekst i vitenarkiv Vis sammendrag

  The fraction of ionizing photons that escape high-redshift galaxies sensitively determines whether galaxies reionized the early Universe. However, this escape fraction cannot be measured from high-redshift galaxies because the opacity of the intergalactic medium is large at high redshifts. Without methods to measure the escape fraction of high-redshift galaxies indirectly, it is unlikely that we will know what reionized the Universe. Here, we analyze the far-ultraviolet (UV) H I (Lyman series) and low-ionization metal absorption lines of nine low-redshift, confirmed Lyman continuum emitting galaxies. We use the H I covering fractions, column densities, and dust attenuations measured in a companion paper to predict the escape fraction of ionizing photons. We find good agreement between the predicted and observed Lyman continuum escape fractions (within 1.4σ) using both the H I and ISM absorption lines. The ionizing photons escape through holes in the H I, but we show that dust attenuation reduces the fraction of photons that escape galaxies. This means that the average high-redshift galaxy likely emits more ionizing photons than low-redshift galaxies. Two other indirect methods accurately predict the escape fractions: the Lyα escape fraction and the optical [O III]/[O II] flux ratio. We use these indirect methods to predict the escape fraction of a sample of 21 galaxies with rest-frame UV spectra but without Lyman continuum observations. Many of these galaxies have low escape fractions (fesc ≤ 1%), but 11 have escape fractions >1%. Future studies will use these methods to measure the escape fractions of high-redshift galaxies, enabling upcoming telescopes to determine whether star-forming galaxies reionized the early Universe. © 2018 ESO

• Rigby, J. R.; Bayliss, M. B.; Sharon, K.; Gladders, M. D.; Chisholm, J. & Dahle, Håkon [Vis alle 10 forfattere av denne artikkelen] (2018). The Magellan Evolution of Galaxies Spectroscopic and Ultraviolet Reference Atlas (MegaSaura). I. the Sample and the Spectra. Astronomical Journal. ISSN 0004-6256. 155(3). doi: 10.3847/1538-3881/aaa2ff. Fulltekst i vitenarkiv Vis sammendrag

  We introduce Project MegaSaura: the Magellan Evolution of Galaxies Spectroscopic and Ultraviolet Reference Atlas. MegaSaura comprises medium-resolution, rest-frame ultraviolet spectroscopy of N = 15 bright gravitationally lensed galaxies at redshifts of 1.68 < z < 3.6, obtained with the MagE spectrograph on the Magellan telescopes. The spectra cover the observed-frame wavelength range 3200 < λ o < 8280 Å; the average spectral resolving power is R = 3300. The median spectrum has a signal-to-noise ratio (S/N) = 21 per resolution element at 5000 Å. As such, the MegaSaura spectra have superior S/N and wavelength coverage compared to what COS/HST provides for starburst galaxies in the local universe. This paper describes the sample, the observations, and the data reduction. We compare the measured redshifts for the stars, the ionized gas as traced by nebular lines, and the neutral gas as traced by absorption lines; we find the expected bulk outflow of the neutral gas, and no systemic offset between the redshifts measured from nebular lines and the redshifts measured from the stellar continuum. We provide the MegaSaura spectra to the astronomical community through a data release.

• Burg, Remco F.J. van der; McGee, Sean; Aussel, Hervé; Dahle, Håkon; Arnaud, Monique & Pratt, Gabriel W. [Vis alle 7 forfattere av denne artikkelen] (2018). The stellar mass function of galaxies in Planck-selected clusters at 0.5 < z < 0.7: new constraints on the timescale and location of satellite quenching. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 618:A140. doi: 10.1051/0004-6361/201833572. Fulltekst i vitenarkiv Vis sammendrag

  We study the abundance of star-forming and quiescent galaxies in a sample of 21 clusters at 0.5 <  z <  0.7, detected with the Planck satellite. Thanks to the large volume probed by Planck, these systems are extremely massive, and provide an excellent laboratory to study any environmental effects on their galaxies’ properties. We measure the cluster galaxy stellar mass function (SMF), which is a fundamental observable to study and constrain the formation and evolution of galaxies. Our measurements are based on homogeneous and deep multi-band photometry spanning from the u- to the Ks-band for each cluster and are supported by spectroscopic data from different programs. The galaxy population is separated into quiescent and star-forming galaxies based on their rest-frame U−V and V−J colours. The SMF is compared to that of field galaxies at the same redshifts using data from the COSMOS/UltraVISTA survey. We find that the shape of the SMF of star-forming galaxies does not depend on environment, while the SMF of quiescent galaxies has a significantly steeper low-mass slope in the clusters compared to the field. This indicates that a different quenching mechanism is at play in clusters compared to the field, accentuated by a quenched fraction that is much higher in the clusters. We estimate the environmental quenching efficiency (fEQ), that is, the probability for a galaxy that would normally be star forming in the field to be quenched due to its environment. The fEQ shows no stellar-mass dependence in any environment, but it increases from 40% in the cluster outskirts to ∼90% in the cluster centres. The radial signature of fEQ provides constraints on where the dominant quenching mechanism operates in these clusters and on what timescale. Exploring these using a simple model based on galaxy orbits obtained from an N-body simulation, we find a clear degeneracy between both parameters. For example, the quenching process may either be triggered on a long (∼3 Gyr) timescale at large radii (r  ∼  8 R500), or happen well within 1 Gyr at r <  R500. The radius where quenching is triggered is at least rquench >  0.67 R500 (95%CL). The ICM density at this location (as probed with XMM-Newton) suggests that ram-pressure stripping of the cold gas is a likely cause of quenching. In addition to this cluster-quenching mechanism, we find that 20–32%, depending on the cluster-specific quenching process, of accreted galaxies were already pre-processed (i.e. quenched by the surrounding overdensities) before they fell into the clusters.

• Rivera-Thorsen, Thøger Emil Juul; Dahle, Håkon; Gronke, Max Balthasar; Bayliss, M; Rigby, J. R. & Simcoe, R [Vis alle 9 forfattere av denne artikkelen] (2017). The Sunburst Arc: Direct Lyman α escape observed in the brightest known lensed galaxy. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 608. doi: 10.1051/0004-6361/201732173. Fulltekst i vitenarkiv Vis sammendrag

  We present rest-frame ultraviolet and optical spectroscopy of the brightest lensed galaxy yet discovered, at redshift z = 2.4. The source reveals a characteristic triple-peaked Lyman α profile that has been predicted in various theoretical works, but to our knowledge has not been unambiguously observed previously. The feature is well fit by a superposition of two components: a double-peak profile emerging from substantial radiative transfer, and a narrow, central component resulting from directly escaping Lyman α photons, but it is poorly fit by either component alone. We demonstrate that the feature is unlikely to contain contamination from nearby sources, and that the central peak is unaffected by radiative transfer effects except for very slight absorption. The feature is detected at signal-to-noise ratios exceeding 80 per pixel at line center, and bears strong resemblance to synthetic profiles predicted by numerical models. © ESO, 2017

• Sharon, Keren; Bayliss, Matthew B.; Dahle, Håkon; Florian, Michael K.; Gladders, Michael D. & Johnson, Traci L. [Vis alle 10 forfattere av denne artikkelen] (2017). Lens model and time delay predictions for the sextuply lensed quasar SDSS J2222+2745. The Astrophysical Journal (ApJ). ISSN 0004-637X. 835(1). doi: 10.3847/1538-4357/835/1/5. Fulltekst i vitenarkiv Vis sammendrag

  SDSS J2222+2745 is a galaxy cluster at z = 0.49, strongly lensing a quasar at z = 2.805 into six widely separated images. In recent Hubble Space Telescope imaging of the field, we identify additional multiply lensed galaxies and confirm the sixth quasar image that was identified by Dahle et al. We used the Gemini-North telescope to measure a spectroscopic redshift of z = 4.56 of one of the lensed galaxies. These data are used to refine the lens model of SDSS J2222+2745, compute the time delay and magnifications of the lensed quasar images, and reconstruct the source image of the quasar host and a lensed galaxy at z = 2.3. This galaxy also appears in absorption in our Gemini spectra of the lensed quasar, at a projected distance of 34 kpc. Our model is in agreement with the recent time delay measurements of Dahle et al., who found τAB = 47.7 ± 6.0 days and τAC = −722 ± 24 days. We use the observed time delays to further constrain the model, and find that the model-predicted time delays of the three faint images of the quasar are τAD = 502 ± 68 days, τAE = 611 ± 75 days, and τAF = 415 ± 72 days. We have initiated a follow-up campaign to measure these time delays with Gemini North. Finally, we present initial results from an X-ray monitoring program with Swift, indicating the presence of hard X-ray emission from the lensed quasar, as well as extended X-ray emission from the cluster itself, which is consistent with the lensing mass measurement and the cluster velocity dispersion. © 2017. The American Astronomical Society. All rights reserved.

• Andrade-Santos, F.; Jones, Christine; Forman, William R.; Lovisari, Lorenzo; Vikhlinin, Alexey & Weeren, Reinout J. van [Vis alle 24 forfattere av denne artikkelen] (2017). The Fraction of Cool-core Clusters in X-Ray versus SZ Samples Using Chandra Observations. The Astrophysical Journal (ApJ). ISSN 0004-637X. 843(1). doi: 10.3847/1538-4357/aa7461. Fulltekst i vitenarkiv Vis sammendrag

  We derive and compare the fractions of cool-core clusters in the Planck Early Sunyaev–Zel'dovich sample of 164 clusters with $z\leqslant 0.35$ and in a flux-limited X-ray sample of 100 clusters with $z\leqslant 0.30$, using Chandra observations. We use four metrics to identify cool-core clusters: (1) the concentration parameter, which is the ratio of the integrated emissivity profile within 0.15 r 500 to that within r 500; (2) the ratio of the integrated emissivity profile within 40 kpc to that within 400 kpc; (3) the cuspiness of the gas density profile, which is the negative of the logarithmic derivative of the gas density with respect to the radius, measured at 0.04 r 500; and (4) the central gas density, measured at 0.01 r 500. We find that the sample of X-ray-selected clusters, as characterized by each of these metrics, contains a significantly larger fraction of cool-core clusters compared to the sample of SZ-selected clusters (44% ± 7% versus 28% ± 4% using the concentration parameter in the 0.15–1.0 r 500 range, 61% ± 8% versus 36% ± 5% using the concentration parameter in the 40–400 kpc range, 64% ± 8% versus 38% ± 5% using the cuspiness, and 53% ± 7% versus 39 ± 5% using the central gas density). Qualitatively, cool-core clusters are more X-ray luminous at fixed mass. Hence, our X-ray, flux-limited sample, compared to the approximately mass-limited SZ sample, is overrepresented with cool-core clusters. We describe a simple quantitative model that uses the excess luminosity of cool-core clusters compared to non-cool-core clusters at fixed mass to successfully predict the observed fraction of cool-core clusters in X-ray-selected samples. © 2017. The American Astronomical Society. All rights reserved.

• Bayliss, Matthew B.; Sharon, Keren; Acharyya, Ayan; Gladders, Michael D.; Rigby, Jane R. & Bian, Fuyan [Vis alle 13 forfattere av denne artikkelen] (2017). Spatially Resolved Patchy Lyα Emission within the Central Kiloparsec of a Strongly Lensed Quasar Host Galaxy at z = 2.8. Astrophysical Journal Letters. ISSN 2041-8205. 845(2). doi: 10.3847/2041-8213/aa831a. Fulltekst i vitenarkiv Vis sammendrag

  We report the detection of extended Lyα emission from the host galaxy of SDSS J2222+2745, a strongly lensed quasar at z = 2.8. Spectroscopic follow-up clearly reveals extended Lyα in emission between two images of the central active galactic nucleus (AGN). We reconstruct the lensed quasar host galaxy in the source plane by applying a strong lens model to HST imaging and resolve spatial scales as small as ~200 pc. In the source plane, we recover the host galaxy morphology to within a few hundred parsecs of the central AGN and map the extended Lyα emission to its physical origin on one side of the host galaxy at radii ~0.5–2 kpc from the central AGN. There are clear morphological differences between the Lyα and rest-frame ultraviolet stellar continuum emission from the quasar host galaxy. Furthermore, the relative velocity profiles of quasar Lyα, host galaxy Lyα, and metal lines in outflowing gas reveal differences in the absorbing material affecting the AGN and host galaxy. These data indicate the presence of patchy local intervening gas in front of the central quasar and its host galaxy. This interpretation is consistent with the central luminous quasar being obscured across a substantial fraction of its surrounding solid angle, resulting in strong anisotropy in the exposure of the host galaxy to ionizing radiation from the AGN. This work demonstrates the power of strong-lensing-assisted studies to probe spatial scales that are currently inaccessible by other means. © 2017. The American Astronomical Society. All rights reserved.

• Giles, P. A.; Maughan, B. J.; Dahle, Håkon; Bonamente, M.; Landry, D. & Jones, C. [Vis alle 9 forfattere av denne artikkelen] (2017). Chandra measurements of a complete sample of X-ray luminous galaxy clusters: The luminosity-mass relation. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 465(1), s. 858–884. doi: 10.1093/mnras/stw2621. Fulltekst i vitenarkiv Vis sammendrag

  We present the results of work involving a statistically complete sample of 34 galaxy clusters, in the redshift range 0.15 ≤ z ≤ 0.3 observed with Chandra. We investigate the luminosity–mass (LM) relation for the cluster sample, with the masses obtained via a full hydrostatic mass analysis. We utilize a method to fully account for selection biases when modelling the LM relation, and find that the LM relation is significantly different from the relation modelled when not account for selection effects. We find that the luminosity of our clusters is 2.2 ± 0.4 times higher (when accounting for selection effects) than the average for a given mass and its mass is 30 per cent lower than the population average for a given luminosity. Equivalently, using the LM relation measured from this sample without correcting for selection biases would lead to the underestimation by 40 per cent of the average mass of a cluster with a given luminosity. Comparing the hydrostatic masses to mass estimates determined from the YX parameter, we find that they are entirely consistent, irrespective of the dynamical state of the cluster. © 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society

• Dahle, Håkon; Aghanim, Nabila; Guennou, L.; Hudelot, P.; Kneissl, R. & Pointecouteau, E. [Vis alle 17 forfattere av denne artikkelen] (2016). Discovery of an exceptionally bright giant arc at z = 2.369, gravitationally lensed by the Planck cluster PSZ1 G311.65 - 18.48. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 590. doi: 10.1051/0004-6361/201628297. Fulltekst i vitenarkiv Vis sammendrag

  As part of an all-sky follow-up of the Planck catalogue of Sunyaev-Zeldovich (SZ) cluster candidates detected in the first 14 months of data, we are observing cluster candidates in the southern sky in the optical imaging and spectroscopy through an ESO Large Programme. Inspection of ESO New Technology Telescope (NTT) R-and z-band imaging data from our programme has revealed an unusually large and bright arc in the field of PSZ1 G311.65−18.48. We establish the basic photometric and morphological properties of the arc and provide conclusive evidence for the gravitational lensing nature of this object. Guided by the NTT images, we have obtained a long-slit spectrum with IMACS on the Magellan-I Baade Telescope, covering a part of the arc and the brightest cluster galaxy of PSZ1 G311.65−18.48. Our imaging data confirm the presence of a galaxy cluster coinciding (within 0.́6) with the position of the Planck SZ source. The arc is separated by ~30″ from the brightest cluster galaxy, which closely coincides with the center of curvature of the arc. A photometric analysis yields integrated (Vega) magnitudes of (R,z,J,Ks) = (17.82,17.38,16.75,15.43) for the arc, more than one magnitude brighter than any previously known lensed arc at z ~ 2–3. The arc is a vigorously star-forming galaxy at z = 2.369, while the Planck SZ cluster lens is at z = 0.443.Even when allowing for lensing magnifications as high as μ = 100 still leads to the conclusion that the source galaxy is among the intrinsically most luminous normal (i.e., non-AGN) galaxies known at z ~ 2–3. Reproduced with permission from Astronomy & Astrophysics, © ESO

• Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J. & Baccigalupi, C. [Vis alle 190 forfattere av denne artikkelen] (2016). Planck intermediate results: XXXVI. Optical identification and redshifts of Planck SZ sources with telescopes at the Canary Islands observatories. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 586. doi: 10.1051/0004-6361/201526345. Fulltekst i vitenarkiv Vis sammendrag

  We present the results of approximately three years of observations of Planck Sunyaev-Zeldovich (SZ) sources with telescopes at the Canary Islands observatories as part of the general optical follow-up programme undertaken by the Planck Collaboration. In total, 78 SZ sources are discussed. Deep-imaging observations were obtained for most of these sources; spectroscopic observations in either in long-slit or multi-object modes were obtained for many. We effectively used 37.5 clear nights. We found optical counterparts for 73 of the 78 candidates. This sample includes 53 spectroscopic redshift determinations, 20 of them obtained with a multi-object spectroscopic mode. The sample contains new redshifts for 27 Planck clusters that were not included in the first Planck SZ source catalogue (PSZ1). Reproduced with permission from Astronomy & Astrophysics, © ESO 2016

• Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J. & Baccigalupi, C. [Vis alle 259 forfattere av denne artikkelen] (2016). Planck 2015 results: XXVII. The second Planck catalogue of Sunyaev-Zeldovich sources. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 594. doi: 10.1051/0004-6361/201525823. Fulltekst i vitenarkiv Vis sammendrag

  We present the all-sky Planck catalogue of Sunyaev-Zeldovich (SZ) sources detected from the 29 month full-mission data. The catalogue (PSZ2) is the largest SZ-selected sample of galaxy clusters yet produced and the deepest systematic all-sky surveyof galaxy clusters. It contains 1653 detections, of which 1203 are confirmed clusters with identified counterparts in external data sets, and is the first SZ-selected cluster survey containing >103 confirmed clusters. We present a detailed analysis of the survey selection function in terms of its completeness and statistical reliability, placing a lower limit of 83% on the purity. Using simulations, we find that the estimates of the SZ strength parameter Y5R500are robust to pressure-profile variation and beam systematics, but accurate conversion to Y500 requires the use of prior information on the cluster extent. We describe the multi-wavelength search for counterparts in ancillary data, which makes use of radio, microwave, infra-red, optical, and X-ray data sets, and which places emphasis on the robustness of the counterpart match. We discuss the physical properties of the new sample and identify a population of low-redshift X-ray under-luminous clusters revealed by SZ selection. These objects appear in optical and SZ surveys with consistent properties for their mass, but are almost absent from ROSAT X-ray selected samples.

• Petrushevska, T.; Amanullah, R.; Goobar, A.; Fabbro, S.; Johansson, J. & Kjellsson, T. [Vis alle 15 forfattere av denne artikkelen] (2016). High-redshift supernova rates measured with the gravitational telescope A 1689. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 594. doi: 10.1051/0004-6361/201628925. Fulltekst i vitenarkiv Vis sammendrag

  Aims. We present a ground-based, near-infrared search for lensed supernovae behind the massive cluster Abell 1689 at z = 0.18, which is one of the most powerful gravitational telescopes that nature provides. Methods. Our survey was based on multi-epoch J-band observations with the HAWK-I instrument on VLT, with supporting optical data from the Nordic Optical Telescope. Results. Our search resulted in the discovery of five photometrically classified, core-collapse supernovae with high redshifts of 0.671 < z < 1.703 and magnifications in the range Δm = − 0.31 to −1.58 mag, as calculated from lensing models in the literature. Owing to the power of the lensing cluster, the survey had the sensitivity to detect supernovae up to very high redshifts, z~3, albeit for a limited region of space. We present a study of the core-collapse supernova rates for 0.4 ≤ z< 2.9, and find good agreement with previous estimates and predictions from star formation history. During our survey, we also discovered two Type Ia supernovae in A 1689 cluster members, which allowed us to determine the cluster Ia rate to be 0.14+0.19-0.09±0.01SNuB h2 (SNuB≡10-12SNe L-1⊙,B yr-1), where the error bars indicate 1σ confidence intervals, statistical and systematic, respectively. The cluster rate normalized by the stellar mass is 0.10+0.13-0.096±0.02 in SNuM h2 (SNuM ≡10-12SNe M-1⊙ yr-1). Furthermore, we explore the optimal future survey for improving the core-collapse supernova rate measurements at z ≳ 2 using gravitational telescopes, and for detections with multiply lensed images, and we find that the planned WFIRST space mission has excellent prospects. Conclusions. Massive clusters can be used as gravitational telescopes to significantly expand the survey range of supernova searches, with important implications for the study of the high-z transient Universe. © ESO, 2016

• Burg, R. F. J. van der; Aussel, H; Pratt, G. W.; Arnaud, Monique; Melin, J.-B. & Aghanim, Nabila [Vis alle 16 forfattere av denne artikkelen] (2016). Prospects for high-z cluster detections with Planck, based on a follow-up of 28 candidates using MegaCam at CFHT. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 587. doi: 10.1051/0004-6361/201527299. Fulltekst i vitenarkiv Vis sammendrag

  The Planck catalogue of SZ sources limits itself to a significance threshold of 4.5 to ensure a low contamination rate by false cluster candidates. This means that only the most massive clusters at redshift z> 0.5, and in particular z> 0.7, are expected to enter into the catalogue, with a large number of systems in that redshift regime being expected around and just below that threshold. In this paper, we follow-up a sample of SZ sources from the Planck SZ catalogues from 2013 and 2015. In the latter maps, we consider detections around and at lower significance than the threshold adopted by the Planck Collaboration. To keep the contamination rate low, our 28 candidates are chosen to have significant WISE detections, in combination with non-detections in SDSS/DSS, which effectively selects galaxy cluster candidates at redshifts z ≳ 0.5. By taking r- and z-band imaging with MegaCam at CFHT, we bridge the 4000 Å rest-frame break over a significant redshift range, thus allowing accurate redshift estimates of red-sequence cluster galaxies up to z ~ 0.8. After discussing the possibility that an overdensity of galaxies coincides -by chance- with a Planck SZ detection, we confirm that 16 of the candidates have likely optical counterparts to their SZ signals, 13 (6) of which have an estimated redshift z> 0.5 (z> 0.7). The richnesses of these systems are generally lower than expected given the halo masses estimated from the Planck maps. However, when we follow a simplistic model to correct for Eddington bias in the SZ halo mass proxy, the richnesses are consistent with a reference mass-richness relation established for clusters detected at higher significance. This illustrates the benefit of an optical follow-up, not only to obtain redshift estimates, but also to provide an independent mass proxy that is not based on the same data the clusters are detected with, and thus not subject to Eddington bias. © ESO, 2016

• Amanullah, R.; Johansson, J.; Goobar, A.; Ferretti, R.; Papodogiannakis, S. & Petrushevska, T. [Vis alle 39 forfattere av denne artikkelen] (2015). Diversity in extinction laws of Type Ia supernovae measured between 0.2 and 2 μm. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 453(3), s. 3300–3328. doi: 10.1093/mnras/stv1505. Fulltekst i vitenarkiv Vis sammendrag

  We present ultraviolet (UV) observations of six nearby Type Ia supernovae (SNe Ia) obtained with the Hubble Space Telescope, three of which were also observed in the near-IR (NIR) with Wide-Field Camera 3. UV observations with the Swift satellite, as well as ground-based optical and NIR data provide complementary information. The combined data set covers the wavelength range 0.2–2 μm. By also including archival data of SN 2014J, we analyse a sample spanning observed colour excesses up to E(B − V) = 1.4 mag. We study the wavelength-dependent extinction of each individual SN and find a diversity of reddening laws when characterized by the total-to-selective extinction RV. In particular, we note that for the two SNe with E(B − V) ≳ 1 mag, for which the colour excess is dominated by dust extinction, we find RV = 1.4 ± 0.1 and RV = 2.8 ± 0.1. Adding UV photometry reduces the uncertainty of fitted RV by ∼50 per cent allowing us to also measure RV of individual low-extinction objects which point to a similar diversity, currently not accounted for in the analyses when SNe Ia are used for studying the expansion history of the Universe. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

• Ade, Peter A.R.; Aghanim, N; Armitage-Caplan, C; Arnaud, M; Ashdown, M & Atrio-Barandela, F [Vis alle 277 forfattere av denne artikkelen] (2015). Planck 2013 results. XXXII. The updated Planck catalogue of Sunyaev-Zeldovich sources. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 581. doi: 10.1051/0004-6361/201525787. Fulltekst i vitenarkiv Vis sammendrag

  © ESO, 2015

• Ade, Peter A.R.; Aghanim, N; Arnaud, M; Ashdown, M; Aumont, J & Baccigalupi, C [Vis alle 199 forfattere av denne artikkelen] (2015). Planck intermediate results. XXVI. Optical identification and redshifts of Planck clusters with the RTT150 telescope. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 582. doi: 10.1051/0004-6361/201424674. Fulltekst i vitenarkiv Vis sammendrag

  © ESO, 2015

• Dahle, Håkon; Gladders, M. D.; Sharon, K.; Bayliss, M. B. & Rigby, J. R. (2015). Time delay measurements for the cluster-lensed sextuple quasar SDSS J2222+2745. The Astrophysical Journal (ApJ). ISSN 0004-637X. 813(1). doi: 10.1088/0004-637X/813/1/67. Fulltekst i vitenarkiv Vis sammendrag

  We report fi rst results from an ongoing monitoring campaign to measure time delays between the six images of the quasar SDSS J2222 + 2745, gravitationally lensed by a galaxy cluster. The time delay between A and B, the two most highly magni fi ed images, is measured to be tAB = 47.7 ± 6.0 days ( 95% con fi dence interval ) , consistent with previous model predictions for this lens system. The strong intrinsic variability of the quasar also allows us to derive a time delay value of tCA = 722 ± 24 CA days between image C and A, in spite of modest overlap between their light curves in the current data set. Image C, which is predicted to lead all the other lensed quasar images, has undergone a sharp, monotonic fl ux increase of 60% – 75% during 2014. A corresponding brightening is fi rmly predicted to occur in images A and B during 2016. The amplitude of this rise indicates that time delays involving all six known images in this system, including those of the demagni fi ed central images D – F, will be obtainable from further ground-based monitoring of this system during the next few years. Reproduced with permission from the Astrophysical Journal. © IOP Publishing

• Radovich, M.; Formicola, I.; Meneghetti, M.; Bartalucci, I.; Bourdin, H. & Mazzotta, P. [Vis alle 15 forfattere av denne artikkelen] (2015). A weak lensing analysis of the PLCK G100.2-30.4 cluster. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 579. doi: 10.1051/0004-6361/201425600. Fulltekst i vitenarkiv Vis sammendrag

  We present a mass estimate of the Planck-discovered cluster PLCK G100.2-30.4, derived from a weak lensing analysis of deep Subaru griz images. We perform a careful selection of the background galaxies using the multi-band imaging data, and undertake the weak lensing analysis on the deep (1 h) r −band image. The shape measurement is based on the Kaiser-Squires-Broadhurst algorithm; we adopt the PSFex software to model the point spread function (PSF) across the field and correct for this in the shape measurement. The weak lensing analysis is validated through extensive image simulations. We compare the resulting weak lensing mass profile and total mass estimate to those obtained from our re-analysis of XMM-Newton observations, derived under the hypothesis of hydrostatic equilibrium. The total integrated mass profiles agree remarkably well, within 1σ across their common radial range. A mass M500 ~ 7 × 1014M⊙ is derived for the cluster from our weak lensing analysis. Comparing this value to that obtained from our reanalysis of XMM-Newton data, we obtain a bias factor of (1−b) = 0.8 ± 0.1. This is compatible within 1σ with the value of (1-b) obtained in Planck 2015 from the calibration of the bias factor using newly available weak lensing reconstructed masses. Reproduced with permission from Astronomy & Astrophysics, © ESO

• Zhang, B; David, L. P.; Jones, C.; Andrade-Santos, F.; O'Sullivan, E. & Dahle, Håkon [Vis alle 16 forfattere av denne artikkelen] (2015). CHANDRA and XMM-NEWTON OBSERVATIONS OF THE MERGING CLUSTER OF GALAXIES PLCK G036.7+14.9. The Astrophysical Journal (ApJ). ISSN 0004-637X. 804(2). doi: 10.1088/0004-637X/804/2/129. Fulltekst i vitenarkiv Vis sammendrag

  We present Chandra and XMM-Newton observations of PLCK G036.7+14.9 from the Chandra–Planck Legacy Program. The high resolution X-ray observations reveal two close (~72'' = 193 kpc in projection) subclusters, G036N and G036S, which were not resolved by previous ROSAT, optical, or recent Planck observations. Reproduced with permission from the Astrophysical Journal. © IOP Publishing

• Perrott, Y. C.; Olamaie, M.; Rumsey, C; Brown, M. L.; Feroz, F. & Grainge, K. J. B. [Vis alle 42 forfattere av denne artikkelen] (2015). Comparison of Sunyaev-Zel'dovich measurements from Planck and from the Arcminute Microkelvin Imager for 99 galaxy clusters. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 580. doi: 10.1051/0004-6361/201424188. Fulltekst i vitenarkiv Vis sammendrag

  We present observations and analysis of a sample of 123 galaxy clusters from the 2013 Planck catalogue of Sunyaev-Zel’dovich sources with the Arcminute Microkelvin Imager (AMI), a ground-based radio interferometer. AMI provides an independent measurement with higher angular resolution, 3 arcmin compared to the Planck beams of 5–10 arcmin. The AMI observations thus provide validation of the cluster detections, improved positional estimates, and a consistency check on the fitted size (θs) and flux (Ytot) parameters in the generalised Navarro, Frenk and White (GNFW) model. We detect 99 of the clusters. We use the AMI positional estimates to check the positional estimates and error-bars produced by the Planck algorithms PowellSnakes and MMF3. We find that Ytot values as measured by AMI are biased downwards with respect to the Planck constraints, especially for high Planck-S/N clusters. We perform simulations to show that this can be explained by deviation from the universal pressure profile shape used to model the clusters. We show that AMI data can constrain the α and β parameters describing the shape of the profile in the GNFW model for individual clusters provided careful attention is paid to the degeneracies between parameters, but one requires information on a wider range of angular scales than are present in AMI data alone to correctly constrain all parameters simultaneously. Reproduced with permission from Astronomy & Astrophysics, © ESO

• Rigby, J. R.; Bayliss, M. B.; Gladders, M. D.; Sharon, K.; Wuyts, E & Dahle, Håkon [Vis alle 8 forfattere av denne artikkelen] (2015). C III] Emission in Star-forming Galaxies Near and Far. Astrophysical Journal Letters. ISSN 2041-8205. 814(1). doi: 10.1088/2041-8205/814/1/L6. Fulltekst i vitenarkiv Vis sammendrag

  We measure [C iii] 1907, C iii] 1909 Å emission lines in 11 gravitationally lensed star-forming galaxies at z ~ 1.6–3, finding much lower equivalent widths than previously reported for fainter lensed galaxies. While it is not yet clear what causes some galaxies to be strong C iii] emitters, C iii] emission is not a universal property of distant star-forming galaxies. We also examine C iii] emission in 46 star-forming galaxies in the local universe, using archival spectra from GHRS, FOS, and STIS on HST and IUE. Twenty percent of these local galaxies show strong C iii] emission, with equivalent widths < −5 Å. Three nearby galaxies show C iii] emission equivalent widths as large as the most extreme emitters yet observed in the distant universe; all three are Wolf–Rayet galaxies. At all redshifts, strong C iii] emission may pick out low-metallicity galaxies experiencing intense bursts of star formation. Such local C iii] emitters may shed light on the conditions of star formation in certain extreme high-redshift galaxies. © American Astronomical Society. All rights reserved.

• Groeneboom, Nicolaas Ervik & Dahle, Håkon (2014). INTRODUCING GAMER: A FAST AND ACCURATE METHOD FOR RAY-TRACING GALAXIES USING PROCEDURAL NOISE. The Astrophysical Journal (ApJ). ISSN 0004-637X. 783(2). doi: 10.1088/0004-637X/783/2/138. Fulltekst i vitenarkiv Vis sammendrag

  We developed a novel approach for fast and accurate ray-tracing of galaxies using procedural noise fields. Our method allows for efficient and realistic rendering of synthetic galaxy morphologies, where individual components such as the bulge, disk, stars, and dust can be synthesized in different wavelengths. These components follow empirically motivated overall intensity profiles but contain an additional procedural noise component that gives rise to complex natural patterns that mimic interstellar dust and star-forming regions. These patterns produce more realistic-looking galaxy images than using analytical expressions alone. The method is fully parallelized and creates accurate high- and low- resolution images that can be used, for example, in codes simulating strong and weak gravitational lensing. In addition to having a user-friendly graphical user interface, the C++ software package GAMER is easy to implement into an existing code. Reproduced with permission from the Astrophysical Journal. © IOP Publishing

• Ade, P. A. R.; Aghanim, N; Armitage-Caplan, C; Arnaud, M; Ashdown, M & Atrio-Barandela, F [Vis alle 275 forfattere av denne artikkelen] (2014). Planck 2013 results. XXIX. The Planck catalogue of Sunyaev-Zeldovich sources. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 571. doi: 10.1051/0004-6361/201321523. Fulltekst i vitenarkiv Vis sammendrag

  We describe the all-sky Planck catalogue of clusters and cluster candidates derived from Sunyaev-Zeldovich (SZ) effect detections using the first 15.5 months of Planck satellite observations. The catalogue contains 1227 entries, making it over six times the size of the Planck Early SZ (ESZ) sample and the largest SZ-selected catalogue to date. It contains 861 confirmed clusters, of which 178 have been confirmed as clusters, mostly through follow-up observations, and a further 683 are previously-known clusters. The remaining 366 have the status of cluster candidates, and we divide them into three classes according to the quality of evidence that they are likely to be true clusters. The Planck SZ catalogue is the deepest all-sky cluster catalogue, with redshifts up to about one, and spans the broadest cluster mass range from (0.1 to 1.6) × 1015 M⊙. Confirmation of cluster candidates through comparison with existing surveys or cluster catalogues is extensively described, as is the statistical characterization of the catalogue in terms of completeness and statistical reliability. The outputs of the validation process are provided as additional information. This gives, in particular, an ensemble of 813 cluster redshifts, and for all these Planck clusters we also include a mass estimated from a newly-proposed SZ-mass proxy. A refined measure of the SZ Compton parameter for the clusters with X-ray counter-parts is provided, as is an X-ray flux for all the Planck clusters not previously detected in X-ray surveys. Reproduced with permission from Astronomy & Astrophysics, © ESO 2014

• Ade, P. A. R.; Aghanim, N; Armitage-Caplan, C; Arnaud, M; Ashdown, M & Atrio-Barandela, F [Vis alle 254 forfattere av denne artikkelen] (2014). Planck 2013 results. XX. Cosmology from Sunyaev-Zeldovich cluster counts. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 571. doi: 10.1051/0004-6361/201321521. Fulltekst i vitenarkiv Vis sammendrag

  We present constraints on cosmological parameters using number counts as a function of redshift for a sub-sample of 189 galaxy clusters from the Planck SZ (PSZ) catalogue. The PSZ is selected through the signature of the Sunyaev-Zeldovich (SZ) effect, and the sub-sample used here has a signal-to-noise threshold of seven, with each object confirmed as a cluster and all but one with a redshift estimate. We discuss the completeness of the sample and our construction of a likelihood analysis. Using a relation between mass M and SZ signal Y calibrated to X-ray measurements, we derive constraints on the power spectrum amplitude σ8 and matter density parameter Ωm in a flat ΛCDM model. We test the robustness of our estimates and find that possible biases in the Y–M relation and the halo mass function are larger than the statistical uncertainties from the cluster sample. Assuming the X-ray determined mass to be biased low relative to the true mass by between zero and 30%, motivated by comparison of the observed mass scaling relations to those from a set of numerical simulations, we find that σ8 = 0.75 ± 0.03, Ωm = 0.29 ± 0.02, and σ8(Ωm/ 0.27)0.3 = 0.764 ± 0.025. The value of σ8 is degenerate with the mass bias; if the latter is fixed to a value of 20% (the central value from numerical simulations) we find σ8(Ωm/0.27)0.3 = 0.78 ± 0.01 and a tighter one-dimensional range σ8 = 0.77 ± 0.02. We find that the larger values of σ8 and Ωm preferred by Planck’s measurements of the primary CMB anisotropies can be accommodated by a mass bias of about 40%. Alternatively, consistency with the primary CMB constraints can be achieved by inclusion of processes that suppress power on small scales relative to the ΛCDM model, such as a component of massive neutrinos. We place our results in the context of other determinations of cosmologicalparameters, and discuss issues that need to be resolved in order to make further progress in this field. Reproduced with permission from Astronomy & Astrophysics, © ESO 2014

• Tremblay, G. R.; Gladders, M. D.; Baum, S. A.; O'Dea, C. P.; Bayliss, M. B. & Cooke, K. C. [Vis alle 13 forfattere av denne artikkelen] (2014). A 30 kpc chain of "beads on a string" star formation between two merging early type galaxies in the core of a strong-lensing galaxy cluster. Astrophysical Journal Letters. ISSN 2041-8205. 790(2). doi: 10.1088/2041-8205/790/2/L26. Fulltekst i vitenarkiv Vis sammendrag

  New Hubble Space Telescope ultraviolet and optical imaging of the strong-lensing galaxy cluster SDSS J1531+3414 (z = 0.335) reveals two centrally dominant elliptical galaxies participating in an ongoing major merger. The interaction is at least somewhat rich in cool gas, as the merger is associated with a complex network of 19 massive superclusters of young stars (or small tidal dwarf galaxies) separated by ~1 kpc in projection from one another, combining to an estimated total star formation rate of ~5 M ☉ yr–1. The resolved young stellar superclusters are threaded by narrow Hα, [O II], and blue excess filaments arranged in a network spanning ~27 kpc across the two merging galaxies. This morphology is strongly reminiscent of the well-known "beads on a string" mode of star formation observed on kiloparsec scales in the arms of spiral galaxies, resonance rings, and in tidal tails between interacting galaxies. Nevertheless, the arrangement of this star formation relative to the nuclei of the two galaxies is difficult to interpret in a dynamical sense, as no known "beads on a string" systems associated with kiloparsec-scale tidal interactions exhibit such lopsided morphology relative to the merger participants. In this Letter, we present the images and follow-up spectroscopy and discuss possible physical interpretations for the unique arrangement of the young stellar clusters. While we suggest that this morphology is likely to be dynamically short-lived, a more quantitative understanding awaits necessary multiwavelength follow-up, including optical integral field spectroscopy, ALMA submillimeter interferometry, and Chandra X-ray imaging. © American Astronomical Society. All rights reserved.

• Ade, P. A. R.; Aghanim, N; Alves, M. I. R.; Armitage-Caplan, C; Arnaud, M & Ashdown, M [Vis alle 400 forfattere av denne artikkelen] (2014). Planck 2013 results. I. Overview of products and scientific results. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 571. doi: 10.1051/0004-6361/201321529. Fulltekst i vitenarkiv Vis sammendrag

  The European Space Agency’s Planck satellite, dedicated to studying the early Universe and its subsequent evolution, was launched 14 May 2009 and has been scanning the microwave and submillimetre sky continuously since 12 August 2009. In March 2013, ESA and the Planck Collaboration released the initial cosmology products based on the first 15.5 months of Planck data, along with a set of scientific and technical papers and a web-based explanatory supplement. This paper gives an overview of the mission and its performance, the processing, analysis, and characteristics of the data, the scientific results, and the science data products and papers in the release. The science products include maps of the cosmic microwave background (CMB) and diffuse extragalactic foregrounds, a catalogue of compact Galactic and extragalactic sources, and a list of sources detected through the Sunyaev-Zeldovich effect. The likelihood code used to assess cosmological models against the Planck data and a lensing likelihood are described. Scientific results include robust support for the standard six-parameter ΛCDM model of cosmology and improved measurements of its parameters, including a highly significant deviation from scale invariance of the primordial power spectrum. The Planck values for these parameters and others derived from them are significantly different from those previously determined. Several large-scale anomalies in the temperature distribution of the CMB, first detected by WMAP, are confirmed with higher confidence. Planck sets new limits on the number and mass of neutrinos, and has measured gravitational lensing of CMB anisotropies at greater than 25σ. Planck finds no evidence for non-Gaussianity in the CMB. Planck’s results agree well with results from the measurements of baryon acoustic oscillations. Planck finds a lower Hubble constant than found in some more local measures. Some tension is also present between the amplitude of matter fluctuations (σ8) derived from CMB data and that derived from Sunyaev-Zeldovich data. The Planck and WMAP power spectra are offset from each other by an average level of about 2% around the first acoustic peak. Analysis of Planck polarization data is not yet mature, therefore polarization results are not released, although the robust detection of E-mode polarization around CMB hot and cold spots is shown graphically. Reproduced with permission from Astronomy & Astrophysics, © ESO 2014

• Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J. & Baccigalupi, C. [Vis alle 184 forfattere av denne artikkelen] (2014). Planck intermediate results: XIII. Constraints on peculiar velocities. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 561. doi: 10.1051/0004-6361/201321299. Fulltekst i vitenarkiv Vis sammendrag

  Using Planck data combined with the Meta Catalogue of X-ray detected Clusters of galaxies (MCXC), we address the study of peculiar motions by searching for evidence of the kinetic Sunyaev-Zeldovich effect (kSZ). By implementing various filters designed to extract the kSZ generated at the positions of the clusters, we obtain consistent constraints on the radial peculiar velocity average, root mean square (rms), and local bulk flow amplitude at different depths. For the whole cluster sample of average redshift 0.18, the measured average radial peculiar velocity with respect to the cosmic microwave background (CMB) radiation at that redshift, i.e., the kSZ monopole, amounts to 72 ± 60 km s-1. This constitutes less than 1% of the relative Hubble velocity of the cluster sample with respect to our local CMB frame. While the linear ΛCDM prediction for the typical cluster radial velocity rms at z = 0.15 is close to 230 km s-1, the upper limit imposed by Planck data on the cluster subsample corresponds to 800 km s-1 at 95% confidence level, i.e., about three times higher. Planck data also set strong constraints on the local bulk flow in volumes centred on the Local Group. There is no detection of bulk flow as measured in any comoving sphere extending to the maximum redshift covered by the cluster sample. A blind search for bulk flows in this sample has an upper limit of 254 km s-1 (95% confidence level) dominated by CMB confusion and instrumental noise, indicating that the Universe is largely homogeneous on Gpc scales. In this context, in conjunction with supernova observations, Planck is able to rule out a large class of inhomogeneous void models as alternatives to dark energy or modified gravity. The Planck constraints on peculiar velocities and bulk flows are thus consistent with the ΛCDM scenario. Reproduced with permission from Astronomy & Astrophysics, © ESO 2014

• Rigby, J. R.; Bayliss, M. B.; Gladders, M. D.; Sharon, K.; Wuyts, E & Dahle, Håkon (2014). On the lack of correlation between Mg II 2796, 2803 Å and Lyα emission in lensed star-forming galaxies. The Astrophysical Journal (ApJ). ISSN 0004-637X. 790(1). doi: 10.1088/0004-637X/790/1/44. Fulltekst i vitenarkiv
• Sharon, K.; Gladders, M. D.; Rigby, J. R.; Wuyts, E; Bayliss, M. B. & Johnson, T. L. [Vis alle 8 forfattere av denne artikkelen] (2014). The mass distribution of the strong lensing cluster SDSS J1531+3414. The Astrophysical Journal (ApJ). ISSN 0004-637X. 795(1). doi: 10.1088/0004-637X/795/1/50. Fulltekst i vitenarkiv
• Meneghetti, M.; Bartelmann, M.; Dahle, Håkon & Limousin, M. (2013). Arc Statistics. Space Science Reviews. ISSN 0038-6308. 177(1-4), s. 31–74. doi: 10.1007/s11214-013-9981-x. Fulltekst i vitenarkiv
• Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M.; Atrio-Barandela, F. & Aumont, J. [Vis alle 209 forfattere av denne artikkelen] (2013). Planck intermediate results. X. Physics of the hot gas in the Coma cluster. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 554. doi: 10.1051/0004-6361/201220247. Fulltekst i vitenarkiv
• Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M.; Atrio-Barandela, F. & Aumont, J. [Vis alle 203 forfattere av denne artikkelen] (2013). Planck intermediate results. XI. The gas content of dark matter halos: the Sunyaev-Zeldovich-stellar mass relation for locally brightest galaxies. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 557. doi: 10.1051/0004-6361/201220941. Fulltekst i vitenarkiv
• Dahle, Håkon; Gladders, M. D.; Sharon, K.; Bayliss, M. B.; Wuyts, E & Abramson, L. E. [Vis alle 14 forfattere av denne artikkelen] (2013). SDSS J2222+2745: A GRAVITATIONALLY LENSED SEXTUPLE QUASAR WITH A MAXIMUM IMAGE SEPARATION OF 15."1 DISCOVERED IN THE SLOAN GIANT ARCS SURVEY. The Astrophysical Journal (ApJ). ISSN 0004-637X. 773(2). doi: 10.1088/0004-637X/773/2/146. Fulltekst i vitenarkiv Vis sammendrag

  We report the discovery of a unique gravitational lens system, SDSS J2222+2745, producing five spectroscopically confirmed images of a zs = 2.82 quasar lensed by a foreground galaxy cluster at zl = 0.49. We also present photometric and spectroscopic evidence for a sixth lensed image of the same quasar. The maximum separation between the quasar images is 15farcs1. Both the large image separations and the high image multiplicity are in themselves rare among known lensed quasars, and observing the combination of these two factors is an exceptionally unlikely occurrence in present data sets. This is only the third known case of a quasar lensed by a cluster, and the only one with six images. The lens system was discovered in the course of the Sloan Giant Arcs Survey, in which we identify candidate lenses in the Sloan Digital Sky Survey and target these for follow-up and verification with the 2.56 m Nordic Optical Telescope. Multi-band photometry obtained over multiple epochs from 2011 September to 2012 September reveals significant variability at the ~10%-30% level in some of the quasar images, indicating that measurements of the relative time delay between quasar images will be feasible. In this lens system, we also identify a bright (g = 21.5) giant arc corresponding to a strongly lensed background galaxy at zs = 2.30. We fit parametric models of the lens system, constrained by the redshift and positions of the quasar images and the redshift and position of the giant arc. The predicted time delays between different pairs of quasar images range from ~100 days to ~6 yr. Reproduced with permission from the Astrophysical Journal. © IOP Publishing

• Blanchard, P. K.; Bayliss, M. B.; McDonald, M.; Dahle, Håkon; Gladders, M. D. & Sharon, K. [Vis alle 7 forfattere av denne artikkelen] (2013). SEARCHING FOR COOLING SIGNATURES IN STRONG LENSING GALAXY CLUSTERS: EVIDENCE AGAINST BARYONS SHAPING THE MATTER DISTRIBUTION IN CLUSTER CORES. The Astrophysical Journal (ApJ). ISSN 0004-637X. 772(1). doi: 10.1088/0004-637X/772/1/24. Fulltekst i vitenarkiv
• Gladders, M. D.; Rigby, J. R.; Sharon, K.; Wuyts, E; Abramson, L. E. & Dahle, Håkon [Vis alle 17 forfattere av denne artikkelen] (2013). SGAS 143845.1+145407: A BIG, COOL STARBURST AT REDSHIFT 0.816. The Astrophysical Journal (ApJ). ISSN 0004-637X. 764(2). doi: 10.1088/0004-637X/764/2/177. Fulltekst i vitenarkiv
• Ade, P. A. R.; Aghanim, N; Arnaud, M; Ashdown, M; Atrio-Barandela, F & Aumont, J [Vis alle 210 forfattere av denne artikkelen] (2013). Planck intermediate results VIII. Filaments between interacting clusters. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 550. doi: 10.1051/0004-6361/201220194. Fulltekst i vitenarkiv
• Hoekstra, H.; Bartelmann, M.; Dahle, Håkon; Israel, H.; Limousin, M. & Meneghetti, M. (2013). Masses of Galaxy Clusters from Gravitational Lensing. Space Science Reviews. ISSN 0038-6308. 177(1-4), s. 75–118. doi: 10.1007/s11214-013-9978-5. Fulltekst i vitenarkiv
• Ade, P. A. R.; Aghanim, N; Arnaud, M; Ashdown, M; Atrio-Barandela, F & Aumont, J [Vis alle 217 forfattere av denne artikkelen] (2013). Planck intermediate results V. Pressure profiles of galaxy clusters from the Sunyaev-Zeldovich effect. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 550. doi: 10.1051/0004-6361/201220040. Fulltekst i vitenarkiv
• Ade, P. A. R.; Aghanim, N; Arnaud, M; Ashdown, M; Aumont, J & Baccigalupi, C [Vis alle 193 forfattere av denne artikkelen] (2013). Planck intermediate results IV. The XMM-Newton validation programme for new Planck galaxy clusters. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 550. doi: 10.1051/0004-6361/201219519. Fulltekst i vitenarkiv
• Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M; Aumont, J & Baccigalupi, C [Vis alle 205 forfattere av denne artikkelen] (2013). Planck intermediate results II. Comparison of Sunyaev-Zeldovich measurements from Planck and from the Arcminute Microkelvin Imager for 11 galaxy clusters. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 550. doi: 10.1051/0004-6361/201219361. Fulltekst i vitenarkiv
• Ade, P. A. R.; Aghanim, N; Arnaud, M; Ashdown, M; Atrio-Barandela, F & Aumont, J [Vis alle 208 forfattere av denne artikkelen] (2013). Planck intermediate results VI. The dynamical structure of PLCKG214.6+37.0, a Planck discovered triple system of galaxy clusters. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 550. doi: 10.1051/0004-6361/201220039. Fulltekst i vitenarkiv
• Ade, P. A. R.; Aghanim, N; Arnaud, M; Ashdown, M; Atrio-Barandela, F & Aumont, J [Vis alle 185 forfattere av denne artikkelen] (2013). Planck intermediate results III. The relation between galaxy cluster mass and Sunyaev-Zeldovich signal. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 550. doi: 10.1051/0004-6361/201219398. Fulltekst i vitenarkiv
• Dahle, Håkon; Sarazin, C. L.; Lopez, L. A.; Kouveliotou, C; Patel, S. K. & Rol, E [Vis alle 14 forfattere av denne artikkelen] (2013). THE BURST CLUSTER: DARK MATTER IN A CLUSTER MERGER ASSOCIATED WITH THE SHORT GAMMA-RAY BURST, GRB 050509B. The Astrophysical Journal (ApJ). ISSN 0004-637X. 772(1). doi: 10.1088/0004-637X/772/1/23. Fulltekst i vitenarkiv
• Aghanim, N.; Arnaud, M.; Ashdown, M.; Atrio-Barandela, F.; Aumont, J. & Baccigalupi, C. [Vis alle 184 forfattere av denne artikkelen] (2012). Planck intermediate results I. Further validation of new Planck clusters with XMM-Newton. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 543. doi: 10.1051/0004-6361/201118731. Fulltekst i vitenarkiv
• Oguri, M.; Bayliss, M. B.; Dahle, Håkon; Sharon, K.; Gladders, M. D. & Natarajan, P. [Vis alle 8 forfattere av denne artikkelen] (2012). Combined strong and weak lensing analysis of 28 clusters from the Sloan Giant Arcs Survey. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 420(4), s. 3213–3239. doi: 10.1111/j.1365-2966.2011.20248.x. Fulltekst i vitenarkiv
• Aghanim, N; Arnaud, M; Ashdown, M; Aumont, J; Baccigalupi, C. & Balbi, A [Vis alle 197 forfattere av denne artikkelen] (2011). Planck early results. X. Statistical analysis of Sunyaev-Zeldovich scaling relations for X-ray galaxy clusters. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 536. doi: 10.1051/0004-6361/201116457. Fulltekst i vitenarkiv
• Morandi, A.; Limousin, M.; Rephaeli, Y.; Umetsu, K; Barkana, R & Broadhurst, T. [Vis alle 7 forfattere av denne artikkelen] (2011). Triaxiality and non-thermal gas pressure in Abell 1689. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 416(4), s. 2567–2573. doi: 10.1111/j.1365-2966.2011.19175.x. Fulltekst i vitenarkiv
• Aghanim, N; Arnaud, M; Ashdown, M; Aumont, J; Baccigalupi, C. & Balbi, A [Vis alle 203 forfattere av denne artikkelen] (2011). Planck early results. IX. XMM-Newton follow-up for validation of Planck cluster candidates. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 536. doi: 10.1051/0004-6361/201116460. Fulltekst i vitenarkiv
• Ade, P. A. R.; Aghanim, N; Arnaud, M; Ashdown, M; Aumont, J & Baccigalupi, C. [Vis alle 236 forfattere av denne artikkelen] (2011). Planck early results. VIII. The all-sky early Sunyaev-Zeldovich cluster sample. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 536. doi: 10.1051/0004-6361/201116459. Fulltekst i vitenarkiv
• Aghanim, N.; Arnaud, M.; Ashdown, M.; Atrio-Barandela, F.; Aumont, J. & Baccigalupi, C. [Vis alle 191 forfattere av denne artikkelen] (2011). Planck early results. XXVI. Detection with Planck and confirmation by XMM-Newton of PLCK G266.6–27.3, an exceptionally X-ray luminous and massive galaxy cluster at z ~ 1. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 536. doi: 10.1051/0004-6361/201117430. Fulltekst i vitenarkiv
• Bayliss, M. B.; Hennawi, J. F.; Gladders, M. D.; Koester, B. P.; Sharon, K. & Dahle, Håkon [Vis alle 7 forfattere av denne artikkelen] (2011). GEMINI/GMOS SPECTROSCOPY OF 26 STRONG-LENSING-SELECTED GALAXY CLUSTER CORES. Astrophysical Journal Supplement Series. ISSN 0067-0049. 193(1). doi: 10.1088/0067-0049/193/1/8. Fulltekst i vitenarkiv
• Thöne, C. C.; Campana, S.; Lazzati, D.; Postigo, A. de Ugarte; Fynbo, J.P.U. & Christensen, L. [Vis alle 19 forfattere av denne artikkelen] (2011). Variable Ly alpha sheds light on the environment surrounding GRB 090426. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 414(1), s. 479–488. doi: 10.1111/j.1365-2966.2011.18408.x. Fulltekst i vitenarkiv
• Aghanim, N; Arnaud, M; Ashdown, M; Aumont, J; Baccigalupi, C. & Balbi, A [Vis alle 204 forfattere av denne artikkelen] (2011). Planck early results. XII. Cluster Sunyaev-Zeldovich optical scaling relations. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 536. doi: 10.1051/0004-6361/201116489. Fulltekst i vitenarkiv
• Ade, P. A. R.; Aghanim, N; Arnaud, M; Ashdown, M; Aumont, J & Baccigalupi, C. [Vis alle 208 forfattere av denne artikkelen] (2011). Planck early results. XI. Calibration of the local galaxy cluster Sunyaev-Zeldovich scaling relations. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 536. doi: 10.1051/0004-6361/201116458. Fulltekst i vitenarkiv
• Amanullah, R.; Goobar, A.; Clement, Bernard; Cuby, J.-G.; Dahle, Håkon & Dahlén, T. [Vis alle 20 forfattere av denne artikkelen] (2011). A HIGHLY MAGNIFIED SUPERNOVA AT z=1.703 BEHIND THE MASSIVE GALAXY CLUSTER A1689. The Astrophysical Journal (ApJ). ISSN 0004-637X. 742(1). doi: 10.1088/2041-8205/742/1/L7. Fulltekst i vitenarkiv
• Bayliss, M. B.; Gladders, M. D.; Oguri, M.; Hennawi, J. F.; Sharon, K. & Koester, B. P. [Vis alle 7 forfattere av denne artikkelen] (2011). THE REDSHIFT DISTRIBUTION OF GIANT ARCS IN THE SLOAN GIANT ARCS SURVEY. The Astrophysical Journal (ApJ). ISSN 0004-637X. 727(1), s. L26–L26. doi: 10.1088/2041-8205/727/1/L26. Fulltekst i vitenarkiv

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• Lilje, Per Barth & Dahle, Håkon (2025). Hva er det James Webb har sett så nært big bang? Det kalles et av de største mysteriene i moderne astrofysikk – De er for tidlige og for store. [Internet]. Forskning.no. Fulltekst i vitenarkiv
• Lilje, Per Barth & Dahle, Håkon (2015). Dette sorte hullet «raper» stjernerester. [Internet]. NRK Viten. Fulltekst i vitenarkiv
• Cheghasiahi, Yashar Akrami; Bull, Philip James; Dahle, Håkon; Eriksen, Hans Kristian Kamfjord; Fantaye, Yabebal Tadesse & Gjerløw, Eirik [Vis alle 12 forfattere av denne artikkelen] (2013). Første kosmologiske resultater fra Planck-satellitten. Fra Fysikkens Verden. ISSN 0015-9247. 2013(3), s. 68–73. Fulltekst i vitenarkiv

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