Sigurd Kirkevold Næss

• Abbasi, R.; Ackermann, M.; Adams, J.; Agarwalla, S. K.; Aguilar, J. A. & Ahlers, M. [Show all 427 contributors for this article] (2026). A Search for Millimeter-bright Blazars as Astrophysical Neutrino Sources. The Astrophysical Journal (ApJ). ISSN 0004-637X. 999(1). doi: 10.3847/1538-4357/ae31e2. Full text in Research Archive Show summary

  The powerful jets of blazars have been historically considered as likely sites of high-energy cosmic-ray acceleration. However, the particulars of the launched jet and the locations of leptonic and hadronic jet loading remain unclear. In the case when leptonic and hadronic particle injection occur jointly, a temporal correlation between synchrotron radiation and neutrino production is expected. We use a first catalog of millimeter wavelength (95–225 GHz) blazar light curves from the Atacama Cosmology Telescope for a time-dependent correlation with 12 yr of muon neutrino events from the IceCube South Pole Neutrino Observatory. Such millimeter emission traces activity of the bright jet base, which is often self-absorbed at lower frequencies and potentially gamma-ray opaque. We perform an analysis of the population, as well as analyses of individual, selected sources. We do not observe a significant signal from the stacked population. TXS 0506+056 is found as the most significant, individual source, though this detection is not globally significant in our analysis of selected active galactic nuclei. Our results suggest that the majority of millimeter-bright blazars are neutrino dim. In general, it is possible that many blazars have lighter, leptonic jets, or that only selected blazars provide exceptional conditions for neutrino production.

• Aguena, M.; Aiola, S.; Allam, S.; Andrade-Oliveira, F.; Bacon, D. & Bahcall, N. [Show all 100 contributors for this article] (2026). The Atacama Cosmology Telescope: DR6 Sunyaev-Zel’dovich Selected Galaxy Clusters Catalog. The Open Journal of Astrophysics. 9. doi: 10.33232/001c.155863. Full text in Research Archive Show summary

  We present the results of a search for galaxy clusters in the Atacama Cosmology Telescope (ACT) Data Release 6 (DR6) microwave sky maps covering 16293 square degrees in three frequency bands, using data obtained over the lifetime of the project (2008-2022). We report redshifts and mass estimates for 10040 clusters detected via their Sunyaev-Zel’dovich (SZ) effect with signal-to-noise greater than 4 at a 2.4 arcminute filter scale. The catalog includes 1180 clusters at redshifts greater than 1, and 123 clusters at redshifts greater than 1.5. Using a relation between cluster SZ signal and mass that is consistent with recent weak-lensing measurements, we estimate that clusters detected with signal-to-noise greater than 5 form a sample which is 90% complete for clusters with masses greater than MSun (measured within a spherical volume with mean density 500 times the critical density). El Gordo, a cluster found in an initial ACT survey of 755 square degrees, remains the most extreme cluster in mass and redshift; we find no cluster with a mass and redshift combination high enough to falsify the standard LCDM cosmology with Gaussian initial perturbations. We make public a variety of data products, including the full cluster candidate list, noise maps, and sky masks, along with our software for cluster detection and instructions for reproducing our cluster catalogs from the public ACT maps.

• Abitbol, M.; Abril-Cabezas, I.; Adachi, S.; Ade, P.; Adler, A.E. & Agrawal, P. [Show all 421 contributors for this article] (2025). The Simons Observatory: science goals and forecasts for the enhanced Large Aperture Telescope. Journal of Cosmology and Astroparticle Physics (JCAP). 2025(08). doi: 10.1088/1475-7516/2025/08/034. Full text in Research Archive Show summary

  We describe updated scientific goals for the wide-field, millimeter-wave survey that will be produced by the Simons Observatory (SO). Significant upgrades to the 6-meter SO Large Aperture Telescope (LAT) are expected to be complete by 2028, and will include a doubled mapping speed with 30,000 new detectors and an automated data reduction pipeline. In addition, a new photovoltaic array will supply most of the observatory's power. The LAT survey will cover about 60% of the sky at a regular observing cadence, with five times the angular resolution and ten times the map depth of the Planck satellite. The science goals are to: (1) determine the physical conditions in the early universe and constrain the existence of new light particles; (2) measure the integrated distribution of mass, electron pressure, and electron momentum in the late-time universe, and, in combination with optical surveys, determine the neutrino mass and the effects of dark energy via tomographic measurements of the growth of structure at redshifts z ≲ 3; (3) measure the distribution of electron density and pressure around galaxy groups and clusters, and calibrate the effects of energy input from galaxy formation on the surrounding environment; (4) produce a sample of more than 30,000 galaxy clusters, and more than 100,000 extragalactic millimeter sources, including regularly sampled AGN light-curves, to study these sources and their emission physics; (5) measure the polarized emission from magnetically aligned dust grains in our Galaxy, to study the properties of dust and the role of magnetic fields in star formation; (6) constrain asteroid regoliths, search for Trans-Neptunian Objects, and either detect or eliminate large portions of the phase space in the search for Planet 9; and (7) provide a powerful new window into the transient universe on time scales of minutes to years, concurrent with observations from the Vera C. Rubin Observatory of overlapping sky.

• Calabrese, Erminia; Hill, J. Colin; Jense, Hidde T.; Posta, Adrien La; Abril-Cabezas, Irene & Addison, Graeme E. [Show all 172 contributors for this article] (2025). The Atacama Cosmology Telescope: DR6 constraints on extended cosmological models. Journal of Cosmology and Astroparticle Physics (JCAP). 2025(11). doi: 10.1088/1475-7516/2025/11/063. Full text in Research Archive Show summary

  We use new cosmic microwave background (CMB) primary temperature and polarization anisotropy measurements from the Atacama Cosmology Telescope (ACT) Data Release 6 (DR6) to test foundational assumptions of the standard cosmological model, ΛCDM, and set constraints on extensions to it. We derive constraints from the ACT DR6 power spectra alone, as well as in combination with legacy data from the Planck mission. To break geometric degeneracies, we include ACT and Planck CMB lensing data and baryon acoustic oscillation data from DESI Year-1. To test the dependence of our results on non-ACT data, we also explore combinations replacing Planck with WMAP and DESI with BOSS, and further add supernovae measurements from Pantheon+ for models that affect the late-time expansion history. We verify the near-scale-invariance (running of the spectral index dn s / d ln k = 0.0062 ± 0.0052) and adiabaticity of the primordial perturbations. Neutrino properties are consistent with Standard Model predictions: we find no evidence for new light, relativistic species that are free-streaming ( N eff = 2.86 ± 0.13, which combined with astrophysical measurements of primordial helium and deuterium abundances becomes N eff = 2.89 ± 0.11), for non-zero neutrino masses (∑ m ν < 0.089 eV at 95% CL), or for neutrino self-interactions. We also find no evidence for self-interacting dark radiation ( N idr < 0.134), or for early-universe variation of fundamental constants, including the fine-structure constant ( α EM / α EM,0 = 1.0043 ± 0.0017) and the electron mass ( m e / m e,0 = 1.0063 ± 0.0056). Our data are consistent with standard big bang nucleosynthesis (we find Y p = 0.2312 ± 0.0092), the COBE/FIRAS -inferred CMB temperature (we find T CMB = 2.698 ± 0.016 K), a dark matter component that is collisionless and with only a small fraction allowed as axion-like particles, a cosmological constant ( w = -0.986 ± 0.025), and the late-time growth rate predicted by general relativity ( γ = 0.663 ± 0.052). We find no statistically significant preference for a departure from the baseline ΛCDM model. In fits to models invoking early dark energy, primordial magnetic fields, or an arbitrary modified recombination history, we find H 0 = 69.9 +0.8 -1.5 , 69.1 ± 0.5, or 69.6 ± 1.0 km/s/Mpc, respectively; using BOSS instead of DESI BAO data reduces the central values of these constraints by 1–1.5 km/s/Mpc while only slightly increasing the error bars. In general, models introduced to increase the Hubble constant or to decrease the amplitude of density fluctuations inferred from the primary CMB are not favored over ΛCDM by our data.

• Louis, Thibaut; Posta, Adrien La; Atkins, Zachary; Jense, Hidde T.; Abril-Cabezas, Irene & Addison, Graeme E. [Show all 168 contributors for this article] (2025). The Atacama Cosmology Telescope: DR6 power spectra, likelihoods and ΛCDM parameters. Journal of Cosmology and Astroparticle Physics (JCAP). 2025(11). doi: 10.1088/1475-7516/2025/11/062. Full text in Research Archive Show summary

  We present power spectra of the cosmic microwave background (CMB) anisotropy in temperature and polarization, measured from the Data Release 6 maps made from Atacama Cosmology Telescope (ACT) data. These cover 19,000 deg 2 of sky in bands centered at 98, 150 and 220 GHz, with white noise levels three times lower than Planck in polarization. We find that the ACT angular power spectra estimated over 10,000 deg 2 , and measured to arcminute scales in TT, TE and EE, are well fit by the sum of CMB and foregrounds, where the CMB spectra are described by the ΛCDM model. Combining ACT with larger-scale Planck data, the joint P-ACT dataset provides tight limits on the ingredients, expansion rate, and initial conditions of the universe. We find similar constraining power, and consistent results, from either the Planck power spectra or from ACT combined with WMAP data, as well as from either temperature or polarization in the joint P-ACT dataset. When combined with CMB lensing from ACT and Planck , and baryon acoustic oscillation data from the Dark Energy Spectroscopic Instrument (DESI DR1), we measure a baryon density of Ω b h 2 = 0.0226 ± 0.0001, a cold dark matter density of Ω c h 2 = 0.118 ± 0.001, a Hubble constant of H 0 = 68.22 ± 0.36 km/s/Mpc, a spectral index of n s = 0.974 ± 0.003, and an amplitude of density fluctuations of σ 8 = 0.813 ± 0.005. Including the DESI DR2 data tightens the Hubble constant to H 0 = 68.43 ± 0.27 km/s/Mpc; ΛCDM parameters agree between the P-ACT and DESI DR2 data at the 1.6 σ level. We find no evidence for excess lensing in the power spectrum, and no departure from spatial flatness. The contribution from Sunyaev-Zel'dovich (SZ) anisotropy is detected at high significance; we find evidence for a tilt with suppressed small-scale power compared to our baseline SZ template spectrum, consistent with hydrodynamical simulations with feedback.

• Næss, Sigurd Kirkevold; Guan, Yilun; Duivenvoorden, Adriaan J.; Hasselfield, Matthew; Wang, Yuhan & Abril-Cabezas, Irene [Show all 166 contributors for this article] (2025). The Atacama Cosmology Telescope: DR6 maps. Journal of Cosmology and Astroparticle Physics (JCAP). 2025(11). doi: 10.1088/1475-7516/2025/11/061. Full text in Research Archive Show summary

  We present Atacama Cosmology Telescope (ACT) Data Release 6 (DR6) maps of the Cosmic Microwave Background temperature and polarization anisotropy at arcminute resolution over three frequency bands centered on 98, 150 and 220 GHz. The maps are based on data collected with the AdvancedACT camera over the period 2017–2022 and cover 19,000 square degrees with a median combined depth of 10 μK arcmin. We describe the instrument, mapmaking and map properties and illustrate them with a number of figures and tables. The ACT DR6 maps and derived products are available on LAMBDA at https://lambda.gsfc.nasa.gov/product/act/actadv_prod_table.html . We also provide an interactive web atlas at https://phy-act1.princeton.edu/public/snaess/actpol/dr6/atlas and HiPS data sets in Aladin (e.g. https://alasky.cds.unistra.fr/ACT/DR4DR6/color_CMB ).

• Hadzhiyska, B.; Ferraro, S.; Guachalla, B. Ried; Schaan, E.; Aguilar, J. & Ahlen, S. [Show all 76 contributors for this article] (2025). Evidence for large baryonic feedback at low and intermediate redshifts from kinematic Sunyaev-Zel’dovich observations with ACT and DESI photometric galaxies. Physical Review D. ISSN 2470-0010. 112(8). doi: 10.1103/kclp-x5j1. Full text in Research Archive Show summary

  Recent advances in cosmological observations have provided an unprecedented opportunity to investigate the distribution of baryons relative to the underlying matter. In this work, we show that the gas is more extended than the dark matter, and the amount of baryonic feedback at 𝑧≲1 disfavors low-feedback models such as that of state-of-the-art hydrodynamical simulation IllustrisTNG compared with high-feedback models such as that of the original Illustris simulation. This has important implications for bridging the gap between theory and observations and understanding galaxy formation and evolution. Furthermore, a better grasp of the baryon-dark matter link is critical to future cosmological analyses, which are currently impeded by our limited knowledge of baryonic feedback. Here, we measure the kinematic Sunyaev-Zel’dovich (kSZ) effect from the Atacama Cosmology Telescope, stacked on the luminous red galaxy sample of the Dark Energy Spectroscopic Instrument (DESI) imaging survey. This is the first analysis to use photometric redshifts for reconstructing galaxy velocities. Due to the large number of galaxies comprising the DESI imaging survey, this is the highest signal-to-noise stacked kSZ measurement to date; we detect the signal at 13⁢𝜎, finding strong evidence that the gas is more spread out than the dark matter, as well as a preference for larger feedback compared to some commonly used state-of-the-art hydrodynamical simulations. Our work opens up the possibility of recalibrating large hydrodynamical simulations using the kSZ effect. In addition, our findings highlight the importance of properly accounting for baryonic feedback with future surveys such as LSST through direct probes such as the kSZ, and shed light on long-standing enigmas in astrophysics, such as the “missing baryon” problem.

• Beringue, Benjamin; Surrao, Kristen M.; Hill, J. Colin; Atkins, Zachary; Battaglia, Nicholas & Bolliet, Boris [Show all 31 contributors for this article] (2025). The Atacama Cosmology Telescope: DR6 power spectrum foreground model and validation. Journal of Cosmology and Astroparticle Physics (JCAP). 2025(10). doi: 10.1088/1475-7516/2025/10/082. Full text in Research Archive Show summary

  We discuss the model of astrophysical emission at millimeter wavelengths used to characterize foregrounds in the multi-frequency power spectra of the Atacama Cosmology Telescope (ACT) Data Release 6 (DR6), expanding on Louis et al. (2025) ( 2503.14452 ). We detail several tests to validate the capability of the DR6 parametric foreground model to describe current observations and complex simulations, and show that cosmological parameter constraints are robust against model extensions and variations. We demonstrate consistency of the model with pre-DR6 ACT data and observations from Planck and the South Pole Telescope. We evaluate the implications of using different foreground templates and extending the model with new components and/or free parameters. In all scenarios, the DR6 ΛCDM and ΛCDM+ N eff cosmological parameters shift by less than 0.5 σ relative to the baseline constraints. Some foreground parameters shift more; we estimate their systematic uncertainties associated with modeling choices. From our constraint on the kinematic Sunyaev-Zel'dovich power, we obtain a conservative limit on the duration of reionization of Δ z rei < 4.4, assuming a reionization midpoint consistent with optical depth measurements and a minimal low-redshift contribution, with varying assumptions for this component leading to tighter limits. Finally, we analyze realistic non-Gaussian, correlated microwave sky simulations containing Galactic and extragalactic foreground fields, built independently of the DR6 parametric foreground model. Processing these simulations through the DR6 power spectrum and likelihood pipeline, we recover the input cosmological parameters of the underlying cosmic microwave background field, a new demonstration for small-scale CMB analysis. These tests validate the robustness of the ACT DR6 foreground model and cosmological parameter constraints.

• Nerval, Simran K.; Hornecker, Erika; Guan, Yilun; Zhang, Zeling; Hincks, Adam & Biermann, Emily [Show all 17 contributors for this article] (2025). The Atacama Cosmology Telescope: Machine-learning-driven Tools for Detecting Millimeter Sources in Timestream Preprocessing. The Astrophysical Journal (ApJ). ISSN 0004-637X. 990(2). doi: 10.3847/1538-4357/adef11. Full text in Research Archive Show summary

  We present a new pipeline utilizing machine learning for classifying short-duration features in raw time-ordered data (TOD) of cosmic microwave background survey observations. The pipeline, specifically designed for the Atacama Cosmology Telescope, works in conjunction with the previous TOD preprocessing techniques that employ statistical thresholding to indiscriminately remove all large spikes in the data, whether they are due to noise features, cosmic rays, or true astrophysical sources, in a process called “data cuts.” This has the undesirable effect of excising real astrophysical sources, including transients, from the data. The classification pipeline demonstrated in this work uses the output from these data cuts and is able to differentiate between electronic noise, cosmic rays, and point sources, enabling the removal of undesired signals while retaining true astrophysical signals during TOD preprocessing. We achieve an overall accuracy of 90% in categorizing data spikes of different origin and, importantly, 94% for identifying those caused by astrophysical sources. Our pipeline also measures the amplitude of any detected source seen more than once and produces a subminute-to-minute light curve, providing information on its short-timescale variability. This automated pipeline for source detection and amplitude estimation will be particularly useful for upcoming surveys with large data volumes, such as the Simons Observatory.

• Biermann, Emily; Li, Yaqiong; Næss, Sigurd Kirkevold; Choi, Steve K.; Clark, Susan E. & Devlin, Mark [Show all 27 contributors for this article] (2025). The Atacama Cosmology Telescope: Systematic Transient Search of Single Observation Maps. The Astrophysical Journal (ApJ). ISSN 0004-637X. 986(1). doi: 10.3847/1538-4357/adce70. Full text in Research Archive Show summary

  We conduct a systematic search for astrophysical transients using data from the Atacama Cosmology Telescope. The data were taken from 2017 to 2022 in three frequency bands spanning 77 to 277 GHz. In this paper, we present a pipeline for transient detection using single-observation maps where each pixel of a map contains one observation with an integration time of approximately 4 minutes. We detect 34 transient events at 27 unique locations. All but two of the transients are associated with Galactic stars and exhibit a wide range of properties. We also detect an event coincident with the classical nova YZ Ret and one event consistent with a flaring active galactic nucleus. We notably do not detect any reverse shock emission from gamma-ray bursts, a nondetection that may be in tension with current models.

• McCarthy, Fiona; Battaglia, Nicholas; Bean, Rachel; Bond, J. Richard; Cai, Hongbo & Calabrese, Erminia [Show all 30 contributors for this article] (2025). The Atacama Cosmology Telescope: Large-scale velocity reconstruction with the kinematic Sunyaev-Zel'dovich effect and DESI LRGs. Journal of Cosmology and Astroparticle Physics (JCAP). 2025(05). doi: 10.1088/1475-7516/2025/05/057. Full text in Research Archive Show summary

  The kinematic Sunyaev-Zel'dovich (kSZ) effect induces a non-zero density-density-temperature bispectrum, which we can use to reconstruct the large-scale velocity field from a combination of cosmic microwave background (CMB) and galaxy density measurements, in a procedure known as “kSZ velocity reconstruction”. This method has been forecast to constrain large-scale modes with future galaxy and CMB surveys, improving their measurement beyond what is possible with the galaxy surveys alone. Such measurements will enable tighter constraints on large-scale signals such as primordial non-Gaussianity, deviations from homogeneity, and modified gravity. In this work, we demonstrate a statistically significant measurement of kSZ velocity reconstruction for the first time, by applying quadratic estimators to the combination of the ACT DR6 CMB+kSZ map and the DESI LRG galaxies (with photometric redshifts) in order to reconstruct the velocity field. We do so using a formalism appropriate for the 2-dimensional projected galaxy fields that we use, which naturally incorporates the curved-sky effects important on the largest scales. We find evidence for the signal by cross-correlating with an external estimate of the velocity field from the spectroscopic BOSS survey and rejecting the null (no-kSZ) hypothesis at 3.8σ. Our work presents a first step towards the use of this observable for cosmological analyses.

• Atkins, Zachary; Li, Zack; Alonso, David; Bond, J. Richard; Calabrese, Erminia & Duivenvoorden, Adriaan J. [Show all 21 contributors for this article] (2025). The Atacama Cosmology Telescope: semi-analytic covariance matrices for the DR6 CMB power spectra. Journal of Cosmology and Astroparticle Physics (JCAP). 2025(05). doi: 10.1088/1475-7516/2025/05/015. Full text in Research Archive Show summary

  The Atacama Cosmology Telescope Data Release 6 (ACT DR6) power spectrum is expected to provide state-of-the-art cosmological constraints, with an associated need for precise error modeling. In this paper we design, and evaluate the performance of, an analytic covariance matrix prescription for the DR6 power spectrum that sufficiently accounts for the complicated ACT map properties. We use recent advances in the literature to handle sharp features in the signal and noise power spectra, and account for the effect of map-level anisotropies on the covariance matrix. In including inhomogeneous survey depth information, the resulting covariance matrix prescription is structurally similar to that used in the Planck Cosmic Microwave Background (CMB) analysis. We quantify the performance of our prescription using comparisons to Monte Carlo simulations, finding better than 3% agreement. This represents an improvement from a simpler, pre-existing prescription, which differs from simulations by ∼ 16%. We develop a new method to correct the analytic covariance matrix using simulations, after which both prescriptions achieve better than 1% agreement. This correction method outperforms a commonly used alternative, where the analytic correlation matrix is assumed to be accurate when correcting the covariance. Beyond its use for ACT, this framework should be applicable for future high resolution CMB experiments including the Simons Observatory (SO).

• Kiehlmann, S.; Parra, P. V. de la; Sullivan, A. G.; Synani, A.; Liodakis, I. & Mróz, P. [Show all 34 contributors for this article] (2025). PKS 2131−021-Discovery of Strong Coherent Sinusoidal Variations from Radio to Optical Frequencies: Compelling Evidence for a Blazar Supermassive Black Hole Binary. The Astrophysical Journal (ApJ). ISSN 0004-637X. 985(1). doi: 10.3847/1538-4357/adc567. Full text in Research Archive Show summary

  Haystack and Owens Valley Radio Observatory observations recently revealed strong, intermittent, sinusoidal total flux-density variations that maintained their coherence between 1975 and 2021 in the blazar PKS 2131−021 (z = 1.283). This was interpreted as possible evidence of a supermassive black hole binary (SMBHB). Extended observations through 2023 show a coherence over 47.9 yr, with an observed period P15 GHz = (1739.8 ± 17.4) days. We reject, with p-value = 2.09 × 10−7, the hypothesis that the variations are due to random fluctuations in the red noise tail of the power spectral density. There is clearly a physical phenomenon in PKS 2131−021 producing coherent sinusoidal flux-density variations. We find the coherent sinusoidal intensity variations extend from below 2.7 GHz to optical frequencies, from which we derive an observed period Poptical = (1764 ± 36) days. Across this broad frequency range, there is a smoothly varying monotonic phase shift in the sinusoidal variations with frequency. Hints of periodic variations are also observed at γ-ray energies. The importance of well-vetted SMBHB candidates to searches for gravitational waves is pointed out. We estimate the fraction of blazars that are SMBHB candidates to be >1 in 100. Thus, monitoring programs covering tens of thousands of blazars could discover hundreds of SMBHB candidates.

• Orlowski-Scherer, John; Maccarone, Thomas; Bright, Joe; Kamiński, Tomasz; Koss, Michael & Mohan, Atul [Show all 28 contributors for this article] (2025). Atacama Large Aperture Submillimeter Telescope (AtLAST) science: Probing the transient and time-variable sky. Open Research Europe. 4. doi: 10.12688/openreseurope.17686.2. Full text in Research Archive Show summary

  The study of transient and variable events, including novae, active galactic nuclei, and black hole binaries, has historically been a fruitful path for elucidating the evolutionary mechanisms of our universe. The study of such events in the millimeter and submillimeter is, however, still in its infancy. Submillimeter observations probe a variety of materials, such as optically thick dust, which are hard to study in other wavelengths. Submillimeter observations are sensitive to a number of emission mechanisms, from the aforementioned cold dust, to hot free-free emission, and synchrotron emission from energetic particles. Study of these phenomena has been hampered by a lack of prompt, high sensitivity submillimeter follow-up, as well as by a lack of high-sky-coverage submillimeter surveys. In this paper, we describe how the proposed Atacama Large Aperture Submillimeter Telescope (AtLAST) could fill in these gaps in our understanding of the transient universe. We discuss a number of science cases that would benefit from AtLAST observations, and detail how AtLAST is uniquely suited to contributing to them. In particular, AtLAST’s large field of view will enable serendipitous detections of transient events, while its anticipated ability to get on source quickly and observe simultaneously in multiple bands make it also ideally suited for transient follow-up. We make theoretical predictions for the instrumental and observatory properties required to significantly contribute to these science cases, and compare them to the projected AtLAST capabilities. Finally, we consider the unique ways in which transient science cases constrain the observational strategies of AtLAST, and make prescriptions for how AtLAST should observe in order to maximize its transient science output without impinging on other science cases.

• Morris, Thomas W.; Battistelli, Elia; Bustos, Ricardo; Choi, Steve K.; Duivenvoorden, Adriaan J. & Dunkley, Jo [Show all 20 contributors for this article] (2025). The Atacama Cosmology Telescope: Quantifying atmospheric emission above Cerro Toco. Physical Review D. ISSN 2470-0010. 111(8). doi: 10.1103/PhysRevD.111.082001. Full text in Research Archive Show summary

  At frequencies below 1 Hz, fluctuations in atmospheric emission in the Chajnantor region in northern Chile are the primary source of interference for bolometric millimeter-wave observations. This paper focuses on characterizing the statistics of these fluctuations using measurements from the Atacama Cosmology Telescope (ACT) and the Atacama Pathfinder Experiment (APEX) water vapor radiometer. We show that the total precipitable water vapor (PWV) is not in general an accurate estimator of the level of fluctuations in millimeter-wave atmospheric emission. We also show that the microwave frequency spectrum of atmospheric fluctuations is in good agreement with predictions by the am code for frequency bands above 90 GHz. We introduce a new method for separating atmospheric and systematic fluctuations, allowing us to fit a robust atmospheric flat field, as well as to study in the atmosphere in greater detail than previous works. We present a direct measurement of the temporal outer scale of turbulence of 𝜏0 ≈50  s corresponding to a spatial scale of 𝐿0 ≈500  m. Lastly, we show the variance of fluctuations in ACT’s mm-wave bands correlate with the variance of fluctuations in PWV measured by APEX, even though the observatories are 6 km apart and observe different lines of sight.

• Qu, Frank J.; Sherwin, Blake D.; Madhavacheril, Mathew S.; Han, Dongwon; Crowley, Kevin T. & Abril-Cabezas, Irene [Show all 158 contributors for this article] (2024). The Atacama Cosmology Telescope: A Measurement of the DR6 CMB Lensing Power Spectrum and Its Implications for Structure Growth. The Astrophysical Journal (ApJ). ISSN 0004-637X. 962(2). doi: 10.3847/1538-4357/acfe06. Full text in Research Archive
• MacCrann, Niall; Sherwin, Blake D.; Qu, Frank J.; Namikawa, Toshiya; Madhavacheril, Mathew S. & Abril-Cabezas, Irene [Show all 50 contributors for this article] (2024). The Atacama Cosmology Telescope: Mitigating the Impact of Extragalactic Foregrounds for the DR6 Cosmic Microwave Background Lensing Analysis. The Astrophysical Journal (ApJ). ISSN 0004-637X. 966(1). doi: 10.3847/1538-4357/ad2610. Full text in Research Archive Show summary

  We investigate the impact and mitigation of extragalactic foregrounds for the cosmic microwave background (CMB) lensing power spectrum analysis of Atacama Cosmology Telescope (ACT) data release 6 (DR6) data. Two independent microwave sky simulations are used to test a range of mitigation strategies. We demonstrate that finding and then subtracting point sources, finding and then subtracting models of clusters, and using a profile bias-hardened lensing estimator together reduce the fractional biases to well below statistical uncertainties, with the inferred lensing amplitude, Alens, biased by less than 0.2σ. We also show that another method where a model for the cosmic infrared background (CIB) contribution is deprojected and high-frequency data from Planck is included has similar performance. Other frequency-cleaned options do not perform as well, either incurring a large noise cost or resulting in biased recovery of the lensing spectrum. In addition to these simulation-based tests, we also present null tests on the ACT DR6 data for sensitivity of our lensing spectrum estimation to differences in foreground levels between the two ACT frequencies used, while nulling the CMB lensing signal. These tests pass whether the nulling is performed at the map or bandpower level. The CIB-deprojected measurement performed on the DR6 data is consistent with our baseline measurement, implying that contamination from the CIB is unlikely to significantly bias the DR6 lensing spectrum. This collection of tests gives confidence that the ACT DR6 lensing measurements and cosmological constraints presented in companion papers to this work are robust to extragalactic foregrounds.

• Murphy, Colin C.; Choi, Steve K.; Datta, Rahul; Devlin, Mark J.; Hasselfield, Matthew & Koopman, Brian J. [Show all 13 contributors for this article] (2024). Optical modeling of systematic uncertainties in detector polarization angles for the Atacama Cosmology Telescope. Applied Optics. ISSN 1559-128X. 63(19), p. 5079–5087. doi: 10.1364/AO.521079. Full text in Research Archive Show summary

  We present an estimate of the Atacama Cosmology Telescope (ACT) detector polarization angle systematic uncertainty from optics perturbation analysis using polarization-sensitive ray tracing in CODE V optical design software. Uncertainties in polarization angle calibration in CMB measurements can limit constraints on cosmic birefringence and other cosmological parameters sensitive to polarization leakage. Our framework estimates the angle calibration systematic uncertainties from possible displacements in lens positions and orientations, and anti-reflection coating (ARC) thicknesses and refractive indices. With millimeter displacements in lens positions and percent-level perturbations in ARC thicknesses and indices from design, we find the total systematic uncertainty for three ACT detector arrays operating between 90 and 220 GHz to be at the 10th of degree scale. Reduced lens position and orientation uncertainties from physical measurements could lead to a reduction in the systematic uncertainty estimated with the framework presented here. This optical modeling may inform polarization angle systematic uncertainties for current and future microwave polarimeters, such as the CCAT Observatory, Simons Observatory, and CMB-S4.

• Hervías-Caimapo, Carlos; Næss, Sigurd Kirkevold; Hincks, Adam D.; Calabrese, Erminia; Devlin, Mark J. & Dunkley, Jo [Show all 24 contributors for this article] (2024). The Atacama cosmology telescope: flux upper limits from a targeted search for extragalactic transients. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 529(3), p. 3020–3034. doi: 10.1093/mnras/stae583. Full text in Research Archive Show summary

  We have performed targeted searches of known extragalactic transient events at millimetre wavelengths using nine seasons (2013–2021) of 98, 150, and 229 GHz Atacama Cosmology Telescope (ACT) observations that mapped ∼40 per cent of the sky for most of the data volume. Our data cover 88 gamma-ray bursts (GRBs), 12 tidal disruption events (TDEs), and 203 other transients, including supernovae (SNe). We stack our ACT observations to increase the signal-to-noise ratio of the maps. In all cases but one, we do not detect these transients in the ACT data. The single candidate detection (event AT2019ppm), seen at ∼5σ significance in our data, appears to be due to active galactic nuclei activity in the host galaxy coincident with a transient alert. For each source in our search we provide flux upper limits. For example, the medians for the 95 per cent confidence upper limits at 98 GHz are 15, 18, and 16 mJy for GRBs, SNe, and TDEs, respectively, in the first month after discovery. The projected sensitivity of future wide-area cosmic microwave background surveys should be sufficient to detect many of these events using the methods described in this paper.

• Rosado, Rodrigo Córdova; Hensley, Brandon S.; Clark, Susan E.; Duivenvoorden, Adriaan J.; Atkins, Zachary & Battistelli, Elia Stefano [Show all 18 contributors for this article] (2024). The Atacama Cosmology Telescope: Galactic Dust Structure and the Cosmic PAH Background in Cross-correlation with WISE. The Astrophysical Journal (ApJ). ISSN 0004-637X. 960(2). doi: 10.3847/1538-4357/ad05cd. Full text in Research Archive Show summary

  We present a cross-correlation analysis between 1´resolution total intensity and polarization observations from the Atacama Cosmology Telescope (ACT) at 150 and 220 GHz and 15'' mid-infrared photometry from the Wide-field Infrared Survey Explorer (WISE) over 107 12fdg5 × 12fdg5 patches of sky. We detect a spatially isotropic signal in the WISE×ACT TT cross-power spectrum at 30σ significance that we interpret as the correlation between the cosmic infrared background at ACT frequencies and polycyclic aromatic hydrocarbon (PAH) emission from galaxies in WISE, i.e., the cosmic PAH background. Within the Milky Way, the Galactic dust TT spectra are generally well described by power laws in ℓ over the range 103 < ℓ < 104, but there is evidence both for variability in the power-law index and for non-power-law behavior in some regions. We measure a positive correlation between WISE total intensity and ACT E-mode polarization at 1000 < ℓ ≲ 6000 at >3σ in each of 35 distinct ∼100 deg2 regions of the sky, suggesting that alignment between Galactic density structures and the local magnetic field persists to subparsec physical scales in these regions. The distribution of TE amplitudes in this ℓ range across all 107 regions is biased to positive values, while there is no evidence for such a bias in the TB spectra. This work constitutes the highest-ℓ measurements of the Galactic dust TE spectrum to date and indicates that cross-correlation with high-resolution mid-infrared measurements of dust emission is a promising tool for constraining the spatial statistics of dust emission at millimeter wavelengths.

• Dachlythra, Nadia; Duivenvoorden, Adriaan J.; Gudmundsson, Jon E.; Hasselfield, Matthew; Coppi, Gabriele & Adler, Alexandre E. [Show all 30 contributors for this article] (2024). The Simons Observatory: Beam Characterization for the Small Aperture Telescopes. The Astrophysical Journal (ApJ). ISSN 0004-637X. 961(1). doi: 10.3847/1538-4357/ad0969. Full text in Research Archive Show summary

  Abstract We use time-domain simulations of Jupiter observations to test and develop a beam reconstruction pipeline for the Simons Observatory Small Aperture Telescopes. The method relies on a mapmaker that estimates and subtracts correlated atmospheric noise and a beam fitting code designed to compensate for the bias caused by the mapmaker. We test our reconstruction performance for four different frequency bands against various algorithmic parameters, atmospheric conditions, and input beams. We additionally show the reconstruction quality as a function of the number of available observations and investigate how different calibration strategies affect the beam uncertainty. For all of the cases considered, we find good agreement between the fitted results and the input beam model within an ∼1.5% error for a multipole range ℓ = 30–700 and an ∼0.5% error for a multipole range ℓ = 50–200. We conclude by using a harmonic-domain component separation algorithm to verify that the beam reconstruction errors and biases observed in our analysis do not significantly bias the Simons Observatory r -measurement

• Coulton, William; Madhavacheril, Mathew S.; Duivenvoorden, Adriaan J.; Hill, J. Colin; Abril-Cabezas, Irene & Ade, Peter A. R. [Show all 154 contributors for this article] (2024). Atacama Cosmology Telescope: High-resolution component-separated maps across one third of the sky. Physical Review D. ISSN 2470-0010. 109(6). doi: 10.1103/PhysRevD.109.063530. Full text in Research Archive Show summary

  Observations of the millimeter sky contain valuable information on a number of signals, including the blackbody cosmic microwave background (CMB), Galactic emissions, and the Compton-y distortion due to the thermal Sunyaev-Zel’dovich (tSZ) effect. Extracting new insight into cosmological and astrophysical questions often requires combining multiwavelength observations to spectrally isolate one component. In this work, we present a new arc-minute-resolution Compton-y map, which traces out the line-of-sight-integrated electron pressure, as well as maps of the CMB in intensity and E-mode polarization, across a third of the sky (around 13,000  deg2). We produce these through a joint analysis of data from the Atacama Cosmology Telescope (ACT) data release 4 and 6 at frequencies of roughly 93, 148, and 225 GHz, together with data from the Planck satellite at frequencies between 30 and 545 GHz. We present detailed verification of an internal linear combination pipeline implemented in a needlet frame that allows us to efficiently suppress Galactic contamination and account for spatial variations in the ACT instrument noise. These maps provide a significant advance, in noise levels and resolution, over the existing Planck component-separated maps and will enable a host of science goals including studies of cluster and galaxy astrophysics, inferences of the cosmic velocity field, primordial non-Gaussianity searches, and gravitational lensing reconstruction of the CMB.

• Marrewijk, J. van; Mascolo, L. Di; Gill, A.S.; Battaglia, N.; Battistelli, E.S. & Bond, J.R. [Show all 21 contributors for this article] (2024). XLSSC 122 caught in the act of growing up: Spatially resolved SZ observations of a z = 1.98 galaxy cluster. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 689. doi: 10.1051/0004-6361/202348213. Full text in Research Archive Show summary

  Context. How protoclusters evolved from sparse galaxy overdensities to mature galaxy clusters is still not well understood. In this context, detecting and characterizing the hot intracluster medium (ICM) at high redshifts (z ∼ 2) is key to understanding how the continuous accretion from the filamentary large-scale structure and the mergers along it impact the first phases of cluster formation. Aims. We study the dynamical state and morphology of the z = 1.98 galaxy cluster XLSSC 122 with high-resolution observations (≈5″) of the ICM through the Sunyaev–Zeldovich (SZ) effect. XLSSC 122 is the highest redshift optically confirmed galaxy cluster found in an unbiased, widefield survey. Methods. Via Bayesian forward modeling, we mapped the ICM on scales from the virial radius down to the core of the cluster. To constrain such a broad range of spatial scales, we employed a new technique that jointly forward-models parametric descriptions of the pressure distribution to interferometric ACA and ALMA observations and multiband imaging data from ACT. Results. We detect the SZ effect with 11σ significance in the ALMA+ACA observations and find a flattened inner pressure profile that is consistent with a noncool core classification with a significance of ≥3σ. In contrast to the previous works, we find better agreement between the SZ effect signal and the X-ray emission as well as the cluster member distribution. Further, XLSSC 122 exhibits an excess of SZ flux in the south of the cluster where no X-ray emission is detected. By reconstructing the interferometric observations and modeling in the uv-plane, we obtain a tentative detection of an infalling group or filamentary-like structure in the southeast that is believed to boost and heat up the ICM while the density of the gas is still low. In addition to characterizing the dynamical state of the cluster, we provide an improved SZ mass estimate M500,c = 1.66−0.20+0.23 × 1014 M⊙. Conclusions. Altogether, the observations indicate that we see XLSSC 122 in a dynamic phase of cluster formation while a large reservoir of gas is already thermalized.

• Madhavacheril, Mathew S.; Qu, Frank J.; Sherwin, Blake D.; MacCrann, Niall; Li, Yaqiong & Abril-Cabezas, Irene [Show all 158 contributors for this article] (2024). The Atacama Cosmology Telescope: DR6 Gravitational Lensing Map and Cosmological Parameters. The Astrophysical Journal (ApJ). ISSN 0004-637X. 962(2). doi: 10.3847/1538-4357/acff5f. Full text in Research Archive
• Marques, G.A.; Madhavacheril, M.S.; Darwish, O.; Shaikh, S.; Aguena, M. & Alves, O. [Show all 97 contributors for this article] (2024). Cosmological constraints from the tomography of DES-Y3 galaxies with CMB lensing from ACT DR4. Journal of Cosmology and Astroparticle Physics (JCAP). 2024(01). doi: 10.1088/1475-7516/2024/01/033. Full text in Research Archive Show summary

  We present a measurement of the cross-correlation between the MagLim galaxies selected from the Dark Energy Survey (DES) first three years of observations (Y3) and cosmic microwave background (CMB) lensing from the Atacama Cosmology Telescope (ACT) Data Release 4 (DR4), reconstructed over ∼ 436 deg2 of the sky. Our galaxy sample, which covers ∼ 4143 deg2, is divided into six redshift bins spanning the redshift range of 0.20 < z < 1.05. We adopt a blinding procedure until passing all consistency and systematics tests. After imposing scale cuts for the cross-power spectrum measurement, we reject the null hypothesis of no correlation at 9.1σ. We constrain cosmological parameters from a joint analysis of galaxy and CMB lensing-galaxy power spectra considering a flat ΛCDM model, marginalized over 23 astrophysical and systematic nuisance parameters. We find the clustering amplitude S8 ≡ σ8(Ωm/0.3)0.5 = 0.75+0.04-0.05. In addition, we constrain the linear growth of cosmic structure as a function of redshift. Our results are consistent with recent DES Y3 analyses and suggest a preference for a lower S8 compared to results from measurements of CMB anisotropies by the Planck satellite, although at a mild level (< 2σ) of statistical significance.

• Orlowski-Scherer, John; Venterea, Ricco C.; Battaglia, Nicholas; Næss, Sigurd Kirkevold; Bhandarkar, Tanay & Biermann, Emily [Show all 27 contributors for this article] (2024). The Atacama Cosmology Telescope: Millimeter Observations of a Population of Asteroids or: ACTeroids. The Astrophysical Journal (ApJ). ISSN 0004-637X. 964(2). doi: 10.3847/1538-4357/ad21fe. Full text in Research Archive Show summary

  Abstract We present fluxes and light curves for a population of asteroids at millimeter wavelengths, detected by the Atacama Cosmology Telescope (ACT) over 18,000 deg 2 of the sky using data from 2017 to 2021. We utilize high cadence maps, which can be used in searching for moving objects such as asteroids and trans-Neptunian Objects, as well as for studying transients. We detect 170 asteroids with a signal-to-noise of at least 5 in at least one of the ACT observing bands, which are centered near 90, 150, and 220 GHz. For each asteroid, we compare the ACT measured flux to predicted fluxes from the near-Earth asteroid thermal model fit to WISE data. We confirm previous results that detected a deficit of flux at millimeter wavelengths. Moreover, we report a spectral characteristic to this deficit, such that the flux is relatively lower at 150 and 220 GHz than at 90 GHz. Additionally, we find that the deficit in flux is greater for S-type asteroids than for C-type.

• Anbajagane, D.; Chang, C.; Baxter, E. J.; Charney, S.; Lokken, M. & Aguena, M. [Show all 114 contributors for this article] (2023). Cosmological shocks around galaxy clusters: a coherent investigation with DES, SPT, and ACT. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 527(3), p. 9378–9404. doi: 10.1093/mnras/stad3726. Full text in Research Archive
• Atkins, Zachary; Duivenvoorden, Adriaan J.; Coulton, William R.; Qu, Frank J.; Aiola, Simone & Calabrese, Erminia [Show all 28 contributors for this article] (2023). The Atacama Cosmology Telescope: map-based noise simulations for DR6. Journal of Cosmology and Astroparticle Physics (JCAP). 2023(11). doi: 10.1088/1475-7516/2023/11/073. Full text in Research Archive Show summary

  Abstract The increasing statistical power of cosmic microwave background (CMB) datasets requires a commensurate effort in understanding their noise properties. The noise in maps from ground-based instruments is dominated by large-scale correlations, which poses a modeling challenge. This paper develops novel models of the complex noise covariance structure in the Atacama Cosmology Telescope Data Release 6 (ACT DR6) maps. We first enumerate the noise properties that arise from the combination of the atmosphere and the ACT scan strategy. We then prescribe a class of Gaussian, map-based noise models, including a new wavelet-based approach that uses directional wavelet kernels for modeling correlated instrumental noise. The models are empirical, whose only inputs are a small number of independent realizations of the same region of sky. We evaluate the performance of these models against the ACT DR6 data by drawing ensembles of noise realizations. Applying these simulations to the ACT DR6 power spectrum pipeline reveals a ∼ 20% excess in the covariance matrix diagonal when compared to an analytic expression that assumes noise properties are uniquely described by their power spectrum. Along with our public code, mnms , this work establishes a necessary element in the science pipelines of both ACT DR6 and future ground-based CMB experiments such as the Simons Observatory (SO).

• Næss, Sigurd Kirkevold & Louis, Thibaut (2023). Large-scale power loss in ground-based CMB mapmaking. The Open Journal of Astrophysics. 6. doi: 10.21105/astro.2210.02243. Full text in Research Archive
• Mallaby-Kay, M.; Amodeo, S.; Hill, J.C.; Aguena, M.; Allam, S. & Alves, O. [Show all 83 contributors for this article] (2023). Kinematic Sunyaev-Zel'dovich effect with ACT, DES, and BOSS: A novel hybrid estimator. Physical Review D. ISSN 2470-0010. 108(2). doi: 10.1103/PhysRevD.108.023516. Full text in Research Archive Show summary

  The kinematic and thermal Sunyaev-Zel’dovich (kSZ and tSZ) effects probe the abundance and thermodynamics of ionized gas in galaxies and clusters. We present a new hybrid estimator to measure the kSZ effect by combining cosmic microwave background temperature anisotropy maps with photometric and spectroscopic optical survey data. The method interpolates a velocity reconstruction from a spectroscopic catalog at the positions of objects in a photometric catalog, which makes it possible to leverage the high number density of the photometric catalog and the precision of the spectroscopic survey. Combining this hybrid kSZ estimator with a measurement of the tSZ effect simultaneously constrains the density and temperature of free electrons in the photometrically selected galaxies. Using the 1000  deg2 of overlap between the Atacama Cosmology Telescope (ACT) Data Release 5, the first three years of data from the Dark Energy Survey (DES), and the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 12, we detect the kSZ signal at 4.8σ and reject the null (no-kSZ) hypothesis at 5.1σ. This corresponds to 2.0σ per 100,000 photometric objects with a velocity field based on a spectroscopic survey with 1/5th the density of the photometric catalog. For comparison, a recent ACT analysis using exclusively spectroscopic data from BOSS measured the kSZ signal at 2.1σ per 100,000 objects. Our derived constraints on the thermodynamic properties of the galaxy halos are consistent with previous measurements. With future surveys, such as the Dark Energy Spectroscopic Instrument and the Rubin Observatory Legacy Survey of Space and Time, we expect that this hybrid estimator could result in measurements with significantly better signal-to-noise than those that rely on spectroscopic data alone.

• Li, Yaqiong; Biermann, Emily; Næss, Sigurd Kirkevold; Aiola, Simone; An, Rui & Battaglia, Nicholas [Show all 37 contributors for this article] (2023). The Atacama Cosmology Telescope: Systematic Transient Search of 3 Day Maps. The Astrophysical Journal (ApJ). ISSN 0004-637X. 956(1). doi: 10.3847/1538-4357/ace599. Full text in Research Archive Show summary

  Abstract We conduct a systematic search for transients in 3 yr of data (2017–2019) from the Atacama Cosmology Telescope (ACT). ACT covers 40% of the sky at three bands spanning from 77–277 GHz. Analysis of 3 day mean-subtracted sky maps, which were match filtered for point sources, yielded 29 transient detections. Eight of these transients are due to known asteroids, and three others were previously published. Four of these events occur in areas with poor noise models and thus we cannot be confident they are real transients. We are left with 14 new transient events occurring at 11 unique locations. All of these events are associated with either rotationally variable stars or cool stars. Ten events have flat or falling spectra indicating radiation from synchrotron emission. One event has a rising spectrum indicating a different engine for the flare.

• Lungu, Marius; Storer, Emilie R.; Hasselfield, Matthew; Duivenvoorden, Adriaan J.; Calabrese, Erminia & Chesmore, Grace E. [Show all 31 contributors for this article] (2022). The Atacama Cosmology Telescope: Measurement and analysis of 1D beams for DR4. Journal of Cosmology and Astroparticle Physics (JCAP). 2022(5). doi: 10.1088/1475-7516/2022/05/044. Full text in Research Archive
• Ebina, Haruki; Keskitalo, Reijo; Borrill, Julian; Choi, Steve K.; Kisner, Theodore S. & Næss, Sigurd Kirkevold [Show all 8 contributors for this article] (2022). Wide field high cadence CMB survey designs for Chilean telescopes. Proceedings of SPIE, the International Society for Optical Engineering. ISSN 0277-786X. 12190. doi: 10.1117/12.2629816. Full text in Research Archive Show summary

  We present new wide field survey strategies for Chilean Large Aperture Telescopes (LAT) measuring the Cosmic Microwave Background (CMB), which we call Sinusoidal Modulated High Cadence Survey Strategies. The strategies were developed during the process of optimizing LAT measurements for the CMB-S4, Simons Observatory, and CCAT-prime collaborations. Observing more than fsky ∼0.5, the telescope consistently achieves high observation efficiency, even with Sun-avoidance enabled. Classical azimuthal scan survey strategies observing fields of equal size suffer from problems of observation depth non-uniformity relative to declination and lack of crosslinking. The new survey strategies described here significantly improve both uniformity and crosslinking while also enabling higher cadence observations for time-domain astrophysics. Uniformity and crosslinking are improved by modulation of azimuthal angular velocity and sinusoidal elevation nods, respectively. In particular, there is nearly uniform observation depth and crosslinking is improved from total lack of crosslinking near −40° declination to clearing the strictest thresholds for crosslinking across the entire field. The simulated strategies are compared to the strategies used for the Atacama Cosmology Telescope and previously studied Simons Observatory survey strategies.

• Hilton, Matt; Sifón, Cristóbal; Næss, Sigurd Kirkevold; Madhavacheril, Mathew; Oguri, M. & Rozo, E. [Show all 149 contributors for this article] (2021). The Atacama Cosmology Telescope: A Catalog of >4000 Sunyaev–Zel'dovich Galaxy Clusters. Astrophysical Journal Supplement Series. ISSN 0067-0049. 253(1). doi: 10.3847/1538-4365/abd023. Full text in Research Archive
• Fuskeland, Unni; Andersen, Kristian Joten; Aurlien, Ragnhild; Banerji, Ranajoy; Brilenkov, Maksym & Eriksen, Hans Kristian Kamfjord [Show all 11 contributors for this article] (2021). Constraints on the spectral index of polarized synchrotron emission from WMAP and Faraday-corrected S-PASS data. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 646. doi: 10.1051/0004-6361/202037629. Full text in Research Archive Show summary

  We constrain the spectral index of polarized synchrotron emission, β s , by correlating the recently released 2.3 GHz S -Band Polarization All Sky Survey ( S -PASS) data with the 23 GHz 9-year Wilkinson Microwave Anisotropy Probe (WMAP) sky maps. We subdivide the S-PASS field, which covers the southern ecliptic hemisphere, into 95 15° ×15° regions and estimate the spectral index of polarized synchrotron emission within each region using a simple but robust T – T plot technique. Three different versions of the S-PASS data are considered, corresponding to: no correction for Faraday rotation; Faraday correction based on the rotation measure model presented by the S-PASS team; or Faraday correction based on a rotation measure model presented by Hutschenreuter and Enßlin. We find that the correlation between S-PASS and WMAP is strongest when applying the S-PASS model. Adopting this correction model, we find that the mean spectral index of polarized synchrotron emission gradually steepens from β s  ≈ −2.8 at low Galactic latitudes to β s  ≈ −3.3 at high Galactic latitudes, in good agreement with previously published results. The flat spectral index at the low Galactic latitudes is likely partly due to depolarization effects. Finally, we consider two special cases defined by the BICEP2 and SPIDER fields and obtain mean estimates of β BICEP2  = −3.22 ± 0.06 and β SPIDER  = −3.21 ± 0.03, respectively. Adopting the bandpass filtered WMAP 23 GHz sky map to only include angular scales between 2° and 10° as a spatial template, we constrain the root-mean-square synchrotron polarization amplitude to be less than 0.03  μ K (0.009  μ K) at 90 GHz (150 GHz) for the BICEP2 field, corresponding roughly to a tensor-to-scalar ratio of r  ≲ 0.02 ( r  ≲ 0.005). Very similar constraints are obtained for the SPIDER field. A comparison with a similar analysis performed in the 23–33 GHz range suggests a flattening of about Δ β s  ∼ 0.1 ± 0.2 from low to higher frequencies, but with no statistical significance due to high uncertainties.

• Ruud, Tone Melvær; Fuskeland, Unni; Wehus, Ingunn Kathrine; Vidal, M.; Araujo, D. & Bischoff, C. [Show all 41 contributors for this article] (2015). THE Q/U IMAGING EXPERIMENT: POLARIZATION MEASUREMENTS of the GALACTIC PLANE at 43 and 95 GHz. The Astrophysical Journal (ApJ). ISSN 0004-637X. 811(2). doi: 10.1088/0004-637X/811/2/89. Full text in Research Archive Show summary

  We present polarization observations of two Galactic plane fields centered on Galactic coordinates (l, b) = (0°, 0°) and (329°, 0°) at both Q (43 GHz) and W bands (95 GHz), covering between 301 and 539 square degrees depending on frequency and field. These measurements were made with the QUIET instrument between 2008 October and 2010 December, and include a total of 1263 hr of observations. The resulting maps represent the deepest large-area Galactic polarization observations published to date at the relevant frequencies with instrumental rms noise varying between 1.8 and 2.8 μK deg, 2.3–6 times deeper than corresponding WMAP and Planck maps. The angular resolution is 27farcm3 and 12farcm8 FWHM at Q and W bands, respectively. We find excellent agreement between the QUIET and WMAP maps over the entire fields, and no compelling evidence for significant residual instrumental systematic errors in either experiment, whereas the Planck 44 GHz map deviates from these in a manner consistent with reported systematic uncertainties for this channel. We combine QUIET and WMAP data to compute inverse-variance-weighted average maps, effectively retaining small angular scales from QUIET and large angular scales from WMAP. From these combined maps, we derive constraints on several important astrophysical quantities, including a robust detection of polarized synchrotron spectral index steepening of ≈0.2 off the plane, as well as the Faraday rotation measure toward the Galactic center (RM = −4000 ± 200 rad m−2), all of which are consistent with previously published results. Both the raw QUIET and the co-added QUIET+WMAP maps are made publicly available together with all necessary ancillary information. Reproduced with permission from the Astrophysical Journal. © IOP Publishing

• Huffenberger, K. M.; Araujo, D.; Bischoff, C.; Buder, I.; Chinone, Y. & Cleary, K. [Show all 26 contributors for this article] (2015). THE Q/U IMAGING EXPERIMENT: POLARIZATION MEASUREMENTS of RADIO SOURCES at 43 and 95 GHz. The Astrophysical Journal (ApJ). ISSN 0004-637X. 806(1). doi: 10.1088/0004-637X/806/1/112. Full text in Research Archive
• Fuskeland, Unni; Wehus, Ingunn Kathrine; Eriksen, Hans Kristian Kamfjord & Næss, Sigurd Kirkevold (2014). SPATIAL VARIATIONS IN THE SPECTRAL INDEX OF POLARIZED SYNCHROTRON EMISSION IN THE 9 yr WMAP SKY MAPS. The Astrophysical Journal (ApJ). ISSN 0004-637X. 790(2). doi: 10.1088/0004-637X/790/2/104. Full text in Research Archive Show summary

  We estimate the spectral index, β, of polarized synchrotron emission as observed in the 9 yr Wilkinson Microwave Anisotropy Probe sky maps using two methods, linear regression ("T-T plot") and maximum likelihood. We partition the sky into 24 disjoint sky regions and evaluate the spectral index for all polarization angles between 0° and 85° in steps of 5°. Averaging over polarization angles, we derive a mean spectral index of βall-sky = –2.99 ± 0.01 in the frequency range of 23-33 GHz. We find that the synchrotron spectral index steepens by 0.14 from low to high Galactic latitudes, in agreement with previous studies, with mean spectral indices of βplane = –2.98 ± 0.01 and βhigh-lat = –3.12 ± 0.04. In addition, we find a significant longitudinal variation along the Galactic plane with a steeper spectral index toward the Galactic center and anticenter than toward the Galactic spiral arms. This can be well modeled by an offset sinusoidal, β(l) = –2.85 + 0.17sin (2l – 90°). Finally, we study synchrotron emission in the BICEP2 field, in an attempt to understand whether the claimed detection of large-scale B-mode polarization could be explained in terms of synchrotron contamination. Adopting a spectral index of β = –3.12, typical for high Galactic latitudes, we find that the most likely bias corresponds to about 2% of the reported signal (r = 0.003). The flattest index allowed by the data in this region is β = –2.5, and under the assumption of a straight power-law frequency spectrum, we find that synchrotron emission can account for at most 20% of the reported BICEP2 signal. Reproduced with permission from the Astrophysical Journal. © IOP Publishing

• Bischoff, C.; Brizius, A.; Buder, I.; Chinone, Y.; Cleary, K. & Dumoulin, R. N. [Show all 54 contributors for this article] (2013). THE Q/U IMAGING EXPERIMENT INSTRUMENT. The Astrophysical Journal (ApJ). ISSN 0004-637X. 768(1). doi: 10.1088/0004-637X/768/1/9. Full text in Research Archive
• Gjerløw, Eirik; Mikkelsen, Kristin; Eriksen, Hans Kristian Kamfjord; Górski, Krzysztof M.; Huey, G. & Jewell, J. B. [Show all 10 contributors for this article] (2013). COSMIC MICROWAVE BACKGROUND LIKELIHOOD APPROXIMATION FOR BANDED PROBABILITY DISTRIBUTIONS. The Astrophysical Journal (ApJ). ISSN 0004-637X. 777(2). doi: 10.1088/0004-637X/777/2/150. Full text in Research Archive
• Mikkelsen, Kristin; Næss, Sigurd Kirkevold & Eriksen, Hans Kristian Kamfjord (2013). GRID-BASED EXPLORATION OF COSMOLOGICAL PARAMETER SPACE WITH SNAKE. The Astrophysical Journal (ApJ). ISSN 0004-637X. 777(2). doi: 10.1088/0004-637X/777/2/172. Full text in Research Archive
• Araujo, D.; Bischoff, C.; Brizius, A.; Buder, I.; Chinone, Y. & Cleary, K. [Show all 50 contributors for this article] (2012). SECOND SEASON QUIET OBSERVATIONS: MEASUREMENTS OF THE COSMIC MICROWAVE BACKGROUND POLARIZATION POWER SPECTRUM AT 95 GHz. The Astrophysical Journal (ApJ). ISSN 0004-637X. 760(2). doi: 10.1088/0004-637X/760/2/145. Full text in Research Archive
• Wehus, Ingunn Kathrine; Næss, Sigurd Kirkevold & Eriksen, Hans Kristian Kamfjord (2012). BAYESIAN NOISE ESTIMATION FOR NON-IDEAL COSMIC MICROWAVE BACKGROUND EXPERIMENTS. Astrophysical Journal Supplement Series. ISSN 0067-0049. 199(1). doi: 10.1088/0067-0049/199/1/15. Full text in Research Archive
• Næss, Sigurd Kirkevold (2012). Application of the Kolmogorov-Smirnov test to CMB data: Is the universe really weakly random? Astronomy and Astrophysics (A & A). ISSN 0004-6361. 538. doi: 10.1051/0004-6361/201117344. Full text in Research Archive
• Bischoff, C.; Brizius, A.; Buder, I.; Chinone, Y.; Cleary, K. & Dumoulin, R. N. [Show all 50 contributors for this article] (2011). FIRST SEASON QUIET OBSERVATIONS: MEASUREMENTS OF COSMIC MICROWAVE BACKGROUND POLARIZATION POWER SPECTRA AT 43 GHz IN THE MULTIPOLE RANGE 25 ≤ l ≤ 475. The Astrophysical Journal (ApJ). ISSN 0004-637X. 741(2). doi: 10.1088/0004-637X/741/2/111. Full text in Research Archive
• Sutton, D; Zuntz, J. A.; Ferreira, P. G.; Brown, M. L.; Eriksen, Hans Kristian Kamfjord & Johnson, B. R. [Show all 9 contributors for this article] (2010). Fast and precise map-making for massively multi-detector CMB experiments. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 407(3), p. 1387–1402. doi: 10.1111/j.1365-2966.2010.16954.x. Full text in Research Archive
• Dunkley, J.; Amblard, A; Baccigalupi, C.; Betoule, M.; Chuss, D. & Cooray, A. [Show all 31 contributors for this article] (2009). Prospects for polarized foreground removal. AIP Conference Proceedings. ISSN 0094-243X. 1141, p. 222–264. doi: 10.1063/1.3160888. Full text in Research Archive

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• Eriksen, Hans Kristian Kamfjord; Næss, Sigurd Kirkevold & Wehus, Ingunn Kathrine (2011). The QUIET experiment - looking for gravitational waves in a sea of noise. META. ISSN 1890-1956. p. 4–9. Full text in Research Archive
• Næss, Sigurd Kirkevold (2012). Maximum likelihood analysis with the Q/U Imaging ExperimenT. Universitetet i Oslo. Full text in Research Archive

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