Claudia Cicone

• Scialpi, M.; Mannucci, F.; D’Amato, Q.; Marconcini, C.; Cresci, G. & Marconi, A. [Show all 37 contributors for this article] (2026). Cosmic Duets: I. High-spatial resolution spectroscopy of dual and lensed active galactic nuclei with MUSE-NFM. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 709. doi: 10.1051/0004-6361/202558548. Full text in Research Archive Show summary

  We present the first-year results of the MUSE Large Program “Cosmic Duets”, whose goal is to obtain adaptive-optics assisted MUSE observations with a typical angular resolution of 0.1″ − 0.2″ in order to provide integral-field spectroscopy of sub-arcsec separation dual and lensed active galactic nucleus (AGN) candidates. These observations reveal previously unexplored properties of dual and lensed systems that are key to understanding galaxy evolution, supermassive black hole mergers, and strong-lensing modeling. Targets were efficiently selected using the Gaia multipeak (GMP) technique, which identifies pairs of point-like sources with angular separations below 0.8″ in the Gaia catalog. MUSE spatially resolved spectroscopy provides accurate redshifts, ionization diagnostics, and identification of absorption systems along the line of sight. We report results for 30 GMP-selected targets at z = 0.5 − 3.5. All systems show at least two spatially resolved components. Nineteen objects are confirmed as AGN multiplets, including six dual AGN, ten doubly lensed quasars, and three quadruply lensed systems, while the remaining 11 correspond to chance alignments with foreground stars. Among all the spectroscopically confirmed dual AGN in the literature, 27 pairs have projected separations below 7 kpc in this redshift regime, and our sample accounts for 22% of the total. We studied dual and lensed AGN distributions as a function of redshift, magnitude, and projected separation while accounting for selection effects, and we find that bright systems (J ≲ 16.5) are dominated by lensed quasars, whereas the relative fraction of dual AGN increases at fainter magnitudes. This first-year sample demonstrates the high efficiency of GMP preselection combined with MUSE spectroscopy for identifying sub-arcsec dual and lensed AGN. The full program, targeting ∼150 systems, will enable statistical studies of dual AGN incidence as a function of redshift, separation, and luminosity and allow for precise characterization of the mass composition and distribution in strong lensing galaxies.

• D’Amato, Quirino; Mannucci, Filippo; Sonnenfeld, Alessandro; Scialpi, Martina; Nightingale, James W. & Spingola, Cristiana [Show all 43 contributors for this article] (2026). Milky-Way-like stars in a galaxy core 8 billion years ago revealed by gravitational lensing. Nature Astronomy. 10(6), p. 901–912. doi: 10.1038/s41550-026-02819-4. Full text in Research Archive Show summary

  The assembly of stellar-dominated cores in elliptical galaxies is key to understanding how cosmic structures evolved. Gravitational lensing offers unique insights into the nature of their stars. Here we report the discovery of an extremely compact quadruply lensed quasar (radius ~0.2″), whose lensing galaxy at a redshift of 1.055 (5.5 billion years after the Big Bang) features a lensing mass of only ~2 × 10^10 M⊙. Bayesian analysis, based on the exceptional properties of the system and standard scaling relations, makes it possible to sample the central galactic initial mass function with great accuracy and in a previously uncharted regime in terms of mass and redshift. We find it to be consistent with the initial mass function of the Milky Way while excluding bottom-heavy functions. This indicates that the core either grew slowly or underwent early disruptive events altering its stellar build-up, potentially challenging the classical view in which bulges form rapidly and remain unchanged by later interactions.

• Agostino, James; Medling, Anne M.; Barcos-Muñoz, Loreto; Vivian, U.; Vásquez, Mynor Rodríguez & Privon, George C. [Show all 14 contributors for this article] (2026). Constraining Nuclear Molecular Gas Content with High-resolution CO Imaging of GOALS Galaxies. The Astrophysical Journal (ApJ). ISSN 0004-637X. 998(2). doi: 10.3847/1538-4357/ae3c04. Full text in Research Archive Show summary

  We present measurements of the cool molecular gas mass around the nuclei of two gas-rich mergers, III Zw 035 and IRAS F01364−1042, whose enclosed masses (Menc) within the central 40–80 pc would be overmassive if attributed entirely to the supermassive black hole (SMBH) mass and compared to SMBH–galaxy scaling relations. Our gas mass measurements are derived from Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 long-baseline observations of CO(J = 2–1) and 230 GHz continuum emission at 14–20 pc resolution, which probes below the resolving limit of the previous black hole mass measurements. Subtracting molecular gas mass from these enclosed masses is not enough to reconcile with black hole–galaxy relationships, but independently measuring Menc using the cold CO(2–1) gas does shift the black holes down to their expected values. Still, these ALMA data reveal respective molecular gas masses of ∼3 × 107 to ∼6 × 108 M⊙ within 70 pc of these black holes, which could challenge some black hole accretion models that assume nuclear gas like this has no angular momentum.

• Johnstone, Makoto A.; Treister, Ezequiel; Bauer, Franz E.; Chang, Chin-Shin; Cicone, Claudia & Koss, Michael J. [Show all 27 contributors for this article] (2025). Molecular Gas in Major Mergers Hosting Dual and Single AGNs at < 10 kpc Nuclear Separations. The Astrophysical Journal (ApJ). ISSN 0004-637X. 995(1). doi: 10.3847/1538-4357/ae1600. Full text in Research Archive Show summary

  We present high-resolution (∼50–100 pc) Atacama Large Millimeter/submillimeter Array observations of 12 CO(2–1) or 12 CO(1–0) emission in seven local ( z ≲ 0.05) major mergers—five of which are dual active galactic nucleus (AGN) systems, and two of which are single AGN systems. We model the molecular gas kinematics through rotating disk profiles using a Bayesian Markov Chain Monte Carlo approach. The residuals were then used to isolate nonrotating components of the molecular gas—the most likely contributor to future supermassive black hole (SMBH) growth. We find that more-massive SMBHs have higher surface densities of nonrotating molecular gas within their sphere of influence. This potential molecular gas supply, however, does not correlate with the current accretion efficiency of the SMBHs, suggesting that only a fraction of the observed nonrotating gas is currently reaching the SMBH. Finally, we tentatively find no significant differences in the nuclear molecular gas masses of single-AGN and dual-AGN hosts, both within the SMBH sphere of influence and within the central kiloparsec. Our results indicate that the probability of occurrence of the dual AGN phenomenon is likely dependent on AGN variability and/or obscuration rather than the availability of molecular gas in the nuclear regions.

• Ilha, Gabriele S.; Harrison, C. M.; Mainieri, V.; Njeri, Ann; Bertola, E. & Bischetti, M. [Show all 20 contributors for this article] (2025). Connecting outflows with radio emission in active galactic nuclei at cosmic noon. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 704. doi: 10.1051/0004-6361/202555730. Full text in Research Archive Show summary

  Context. Active galactic nucleus (AGN) feedback is a well-known mechanism in the evolution of galaxies. However, constraining its parameters remains a significant challenge. One open question is the driving mechanism of galaxy-scale outflows. At low redshift, radio jets often interact with the interstellar medium (ISM), generating turbulence and driving ionized outflows. Aims. Despite this evidence at low redshift, relatively few studies have investigated the radio-ionized gas connection at cosmic noon. Thus, our main goal is to conduct a pilot study using Very Large Array (VLA) data for three quasars ( z  ∼ 2.0) with moderate to high radio power (∼10 24.86  − 10 28.15 W Hz −1 ) that have ionized outflows identified in observations from the SUPER Survey to investigate whether this connection also exists. Methods. We used [O  III ] λ 5007 data from VLT/SINFONI analyzed in earlier studies along with new 6.2 GHz VLA radio observations at comparable spatial resolution (∼0.3″-0.5″ or 2.5–4.2 kpc). We also incorporated radio data from the literature at different frequencies and resolutions to explore the radio emission. Results. We detected an extended radio structure in our VLA A-array data for two quasars: J1333+1649 and CID-346. The extended structure in J1333+1649 (∼0.5″ or 4.16 kpc) aligns with the smaller-scale emission (∼0.01″ – 0.02″ or 0.08–0.17 kpc) seen in archival images, suggesting a jet propagating from nuclear to galaxy-wide scales. In all three quasars, we found that the brightest radio emission and ionized gas have comparable spatial scales. Furthermore, the position angles of the radio emission and ionized gas present offsets smaller than 30° for the two targets with extended structures. Given that the kinematics of the ionized gas in all three quasars is dominated by outflows, our results suggest a strong connection between radio emission and ionized outflows in typical AGNs at cosmic noon. Conclusions. This result is similar to what has been previously observed in radio-powerful AGN at the same epoch and in AGN at lower redshifts. Based on energetic considerations and comparisons with archival data, radio jets could be a significant mechanism for driving outflows in AGN from cosmic noon to low redshifts. However, with the exception of one object (J1333+1649), we cannot rule out the possibility that the radio emission arises from shocks in the ISM caused by disk winds or radiatively driven outflows. Further studies on larger samples are required to determine whether radio jets are driving the observed outflows.

• Pensabene, A.; Cantalupo, S.; Wang, W.; Bacchini, C.; Fraternali, F. & Bischetti, M. [Show all 14 contributors for this article] (2025). ALMA survey of a massive node of the Cosmic Web at z ∼ 3: II. A dynamically cold and massive disk galaxy in the proximity of a hyper-luminous quasar. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 701. doi: 10.1051/0004-6361/202554769. Full text in Research Archive Show summary

  Advancing our understanding of the formation and evolution of early massive galaxies and black holes requires detailed studies of dense structures in the high-redshift Universe. In this work, we present high angular resolution (≃0.​​″3) ALMA observations targeting the CO(4−3) line and the underlying 3 mm dust continuum toward the Cosmic Web node MQN01, a region identified through deep multiwavelength surveys as having one of the densest concentrations of galaxies and active galactic nuclei at cosmic noon. At the center of this structure, we identified a massive, rotationally supported disk galaxy located approximately at a projected-distance of ∼10 kpc and ∼ − 300 km s −1 from a hyper-luminous quasar at z  = 3.2510. By accurately modeling the cold gas kinematics, we determined a galaxy dynamical mass of 2.5 × 10 11   M ⊙ within the inner ≃4 kpc and a high degree of rotational support of V rot / σ  ≈ 11. This makes it the first quasar companion galaxy confirmed as a massive, dynamically cold rotating disk at such an early cosmic epoch. Despite the small projected separation from the quasar host, we find no clear evidence of strong tidal interactions affecting the galaxy disk. This might suggest that the quasar is a satellite galaxy in the early stages of a merger. Furthermore, our spectroscopic analysis revealed a broad, blueshifted component in the CO(4−3) line profile of the quasar host, which may trace a powerful molecular outflow or kinematic disturbances induced by its interaction with the massive companion galaxy. Our findings show that rotationally supported cold disks are able to survive even in high-density environments of the early Universe.

• Kakkad, D; Mainieri, V; Tanaka, Takumi S; Silverman, John D; Law, D & Riffel, Rogemar A [Show all 30 contributors for this article] (2025). JWST MIRI/MRS observations of hot molecular gas in an AGN host galaxy at Cosmic Noon. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 541(4), p. 3534–3548. doi: 10.1093/mnras/staf1125. Full text in Research Archive Show summary

  Active Galactic Nuclei (AGN) are believed to play a central role in quenching star formation by removing or destroying molecular gas from host galaxies via radiation-pressure driven outflows and/or radio jets. Some studies of cold molecular gas in galaxies at Cosmic Noon (z ∼ 2) show that AGN have less cold gas (&lt;100 K) compared to mass-matched star-forming galaxies. However, cold gas could also be shock-heated to warmer phases, detectable via H2 transitions in the rest-frame near- and mid-infrared spectra. The Medium Resolution Spectrograph (MRS) of the Mid-infrared Instrument (MIRI) aboard JWST has opened a unique window to observe these emission lines in galaxies at Cosmic Noon. We present the first detection of hot molecular gas in cid_346, an X-ray AGN at z ∼ 2.2, via the H2 ro-vibrational transition at 2.12 μm. We measure a hot molecular gas mass of ∼8.0 × 105 M⊙, which is ∼105 − 106 times lower than the cold molecular gas mass. cid_346 is located in an environment with extended gas structures and satellite galaxies. This is supported by detection of hot and cold molecular gas out to distances &gt;10 kpc in MIRI/MRS and ALMA data, respectively and ancillary NIRCam imaging that reveals two satellite galaxies at distances of ∼0.4 arcsec (3.3 kpc) and ∼0.9 arcsec (7.4 kpc) from the AGN. Our results tentatively indicate that while the CO(3-2)-based cold gas phase dominates the molecular gas mass at Cosmic Noon, H2 ro-vibrational transitions are effective in tracing hot molecular gas locally in regions that may lack CO emission.

• Lasrado, Akhil Ignatius; Cicone, Claudia & Weiss, Axel (2025). The extended molecular gas of the Circinus galaxy and NGC 1097 as seen by APEX. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 701. doi: 10.1051/0004-6361/202554402. Full text in Research Archive Show summary

  The outer region of the interstellar medium (ISM) is often witness to dynamically important events in a galaxy’s evolutionary history such as outflows, inflows, tidal interactions, and mergers, as well as dynamical structures affecting its current evolution such as large-scale bars and spiral arms. Studying the imprints of these processes in the diffuse, extended molecular gas is best achieved by a single dish telescope which can cover a large field of view with good sensitivity to large-scale structures. In this work we present results from Atacama Pathfinder EXperiment (APEX) line emission maps of two nearby galaxies: the Circinus galaxy in the CO(3–2) transition, and NGC 1097 in CO(2–1), covering their full optical extents. We detect molecular gas at the largest extents seen for these galaxies yet, at up to 5′ (r ≈ 6 kpc) for the Circinus galaxy, and 4.′5 (r ≈ 18 kpc) for NGC 1097, and compute total CO luminosities of L′CO(3−2) = (1.5 ± 0.4) × 108 K km s−1 pc2 and L′CO(2−1) = (7.0 ± 1.7) × 108 K km s−1 pc2, corresponding to molecular gas masses (2.1 ± 1.0)×109 M⊙ and (4.7 ± 1.9)×109 M⊙, respectively. We further analyze the large-scale gas kinematics through position-velocity diagrams and 3D tilted ring modeling using the 3DBAROLO code. We detect notable features in both galaxies beyond their well-studied bright central regions: in the Circinus galaxy we detect molecular gas embedded in a bar-like structure, whose kinematic signature is also evident in the major axis position-velocity diagram, and in NGC 1097, we observe tidal molecular gas structures involved in the interaction of NGC 1097 with the companion galaxy NGC 1097A. The clear detection of such structures in the molecular gas shows promise in conducting large-scale molecular gas studies toward nearby galaxies with APEX and, in the future, the Atacama Large Aperture Submillimeter Telescope (AtLAST).

• Nyhagen, Camilla Thune; Schimek, Alice; Cicone, Claudia; Decataldo, Davide & Shen, S. (2025). A theoretical investigation of far-infrared fine structure lines at z<6 and of the origin of the [O III] 88 μm/[C II]158 μm enhancement. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 702. doi: 10.1051/0004-6361/202452718. Full text in Research Archive Show summary

  The far-infrared (FIR) fine structure lines [C  II ] 158 μm , [O  III ] 88 μm , [N  II ] 122 μm , and [N  III ] 57 μm are excellent tools for probing the physical conditions of the interstellar medium (ISM). The [O  III ] 88 μm /[C  II ] 158 μm and [O  III ] 88 μm /[N  II ] 122 μm luminosity ratios have shown to be promising tracers of the ionisation state and gas-phase metallicity of the ISM. Observations of galaxies at redshift z  > 6 show unusually high [O  III ] 88 μm /[C  II ] 158 μm luminosity ratios compared to local sources. The origin of the enhanced ratios has been investigated in the literature with different theoretical modelling approaches. However, no model has to date successfully managed to match the observed emission from both [O  III ] 88 μm and [C  II ] 158 μm , as well as their ratio. For this study we used C LOUDY to model the [C  II ] 158 μm , [O  III ] 88 μm , [N  II ] 122 μm , and [N  III ] 57 μm emission lines of P ONOS , a high-resolution ( m gas  = 883.4  M ⊙ ) cosmological zoom-in simulation of a galaxy at redshift z  = 6.5, which is post-processed using KRAMSES - RT . We modify carbon, nitrogen, and oxygen abundances in our C LOUDY models to obtain C/O and N/O abundance ratios respectively lower and higher than solar, more in line with recent high- z observational constraints. We find [O  III ] 88 μm /[C  II ] 158 μm luminosity ratios that are a factor of ∼5 higher compared to models assuming solar abundances. Additionally, we find an overall better agreement of the simulation with high- z observational constraints of the [C  II ] 158 μm -SFR and [O  III ] 88 μm -SFR relations. This shows that a lower C/O abundance ratio is essential to reproduce the enhanced [O  III ] 88 μm /[C  II ] 158 μm luminosity ratios observed at z  > 6. By assuming a super-solar N/O ratio, motivated by recent z  > 6 JWST observations, our models yield an [O  III ] 88 μm /[N  II ] 122 μm ratio of 1.3, which, according to current theoretical models, would be more appropriate for a galaxy with a lower ionisation parameter than the one we estimated for P ONOS . Most current simulations adopt solar abundance patterns that are not adequate for recently observed high- z predictions. Our results showcase the importance of theoretical modelling efforts, coupled with high-resolution zoom-in simulations, and with parallel multi-tracer observations to understand the physical and chemical conditions of the ISM at z  > 6.

• Liu, Daizhong; Saintonge, Amelie; Bot, Caroline; Kemper, Francisca; Lopez-Rodriguez, Enrique & Smith, Matthew [Show all 28 contributors for this article] (2025). Atacama Large Aperture Submillimeter Telescope (AtLAST) science: Gas and dust in nearby galaxies. Open Research Europe. 4. doi: 10.12688/openreseurope.17459.2. Full text in Research Archive Show summary

  Understanding the physical processes that regulate star formation and galaxy evolution are major areas of activity in modern astrophysics. Nearby galaxies offer unique opportunities to inspect interstellar medium (ISM), star formation (SF), radiative, dynamic and magnetic ( B → ) physics in great detail from sub-galactic (kpc) scales to sub-cloud (sub-pc) scales, from quiescent galaxies to starbursts, and from field galaxies to overdensities. In this case study, we discuss the major breakthroughs in this area of research that will be enabled by the Atacama Large Aperture Submillimeter Telescope (AtLAST), a proposed 50-m single-dish submillimeter telescope. The new discovery space of AtLAST comes from its exceptional sensitivity, in particular to extended low surface brightness emission, a very large 2° field of view, and correspondingly high mapping efficiency. This paper focuses on four themes which will particularly benefit from AtLAST: 1) the LMC and SMC, 2) extragalactic magnetic fields, 3) the physics and chemistry of the interstellar medium, and 4) star formation and galaxy evolution. With ~ 1000 − 2000 hour surveys each, AtLAST could deliver deep dust continuum maps of the entire LMC and SMC fields at parsec-scale resolution, high-resolution maps of the magnetic field structure, gas density, temperature and composition of the dense and diffuse ISM in ~ 100 nearby galaxies, as well as the first large-scale blind CO survey in the nearby Universe, delivering molecular gas masses for up to 10 6 galaxies (3 orders of magnitude more than current samples). Through such observing campaigns, AtLAST will have a profound impact on our understanding of the baryon cycle and star formation across a wide range of environments.

• Mascolo, Luca Di; Perrott, Yvette; Mroczkowski, Tony; Raghunathan, Srinivasan; Andreon, Stefano & Ettori, Stefano [Show all 26 contributors for this article] (2025). Atacama Large Aperture Submillimeter Telescope (AtLAST) science: Resolving the hot and ionized Universe through the Sunyaev-Zeldovich effect. Open Research Europe. 4. doi: 10.12688/openreseurope.17449.2. Full text in Research Archive Show summary

  An omnipresent feature of the multi-phase “cosmic web” — the large-scale filamentary backbone of the Universe — is that warm/hot (≳ 10 5 K) ionized gas pervades it. This gas constitutes a relevant contribution to the overall universal matter budget across multiple scales, from the several tens of Mpc-scale intergalactic filaments, to the Mpc intracluster medium (ICM), all the way down to the circumgalactic medium (CGM) surrounding individual galaxies from ∼ 1 kpc up to their respective virial radii (∼ 100 kpc). The study of the hot baryonic component of cosmic matter density represents a powerful means for constraining the intertwined evolution of galactic populations and large-scale cosmological structures, for tracing the matter assembly in the Universe and its thermal history. To this end, the Sunyaev-Zeldovich (SZ) effect provides the ideal observational tool for measurements out to the beginnings of structure formation. The SZ effect is caused by the scattering of the photons from the cosmic microwave background off the hot electrons embedded within cosmic structures, and provides a redshift-independent perspective on the thermal and kinematic properties of the warm/hot gas. Still, current and next-generation (sub)millimeter facilities have been providing only a partial view of the SZ Universe due to any combination of: limited angular resolution, spectral coverage, field of view, spatial dynamic range, sensitivity, or all of the above. In this paper, we motivate the development of a wide-field, broad-band, multi-chroic continuum instrument for the Atacama Large Aperture Submillimeter Telescope (AtLAST) by identifying the scientific drivers that will deepen our understanding of the complex thermal evolution of cosmic structures. On a technical side, this will necessarily require efficient multi-wavelength mapping of the SZ signal with an unprecedented spatial dynamic range (from arcsecond to tens of arcminutes) and we employ detailed theoretical forecasts to determine the key instrumental constraints for achieving our goals.

• Mroczkowski, Tony; Gallardo, Patricio A.; Timpe, Martin; Kiselev, Aleksej; Groh, Manuel & Kaercher, Hans [Show all 26 contributors for this article] (2025). The conceptual design of the 50-meter Atacama Large Aperture Submillimeter Telescope (AtLAST). Astronomy and Astrophysics (A & A). ISSN 0004-6361. 694. doi: 10.1051/0004-6361/202449786. Full text in Research Archive Show summary

  The (sub)millimeter sky contains a vast wealth of information that is both complementary and inaccessible to other wavelengths. Over half the light we receive is observable at millimeter and submillimeter wavelengths, yet we have mapped only a small portion of the sky at sufficient spatial resolution and sensitivity to detect and resolve distant galaxies or star-forming cores within their large- scale environments. For decades, the astronomical community has highlighted the need for a large, high-throughput (sub)millimeter (λ ~ 0.35–10 mm) single dish. The Atacama Large Aperture Submillimeter Telescope (AtLAST), with its 50-m aperture and 2° maximal field of view, aims to be such a facility. We present here the preliminary design concept for AtLAST, developed through an EU Horizon 2020-funded design study. Our design approach begins with a long lineage of (sub)millimeter telescopes, relies on calculations and simulations to realize the optics, and uses finite element analysis to optimize the conceptual designs for the mechanical structure and subsystems. The demanding technical requirements for AtLAST, set by transformative science goals, have motivated the design effort to combine novel concepts with lessons learned from previous efforts. The result is an innovative rocking chair design with six instrument bays, two of which are mounted on Nasmyth platforms, inside a large receiver cabin. Ultimately, AtLAST aims to achieve a surface accuracy of a ≤20 µm root mean square half wavefront error, corresponding to the goal of a Ruze efficiency of >50% at 950 GHz. We conclude that a closed-loop metrology of the active primary surface will be required to achieve our surface accuracy goal. In the next phase of the project, we shall prototype and test such a metrology on existing platforms, with the goal of delivering a mature, construction-ready design by the end of this decade.

• 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.

• Rigamonti, Fabio; Severgnini, Paola; Sottocorno, Erika; Dotti, Massimo; Covino, Stefano & Landoni, Marco [Show all 15 contributors for this article] (2025). ESPRESSO reveals a single but perturbed broad-line region in the supermassive black hole binary candidate PG 1302-102. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 693. doi: 10.1051/0004-6361/202452830. Full text in Research Archive Show summary

  In this work, we present a new, fully Bayesian analysis of the highest-resolution optical spectrum of the supermassive black hole (SMBH) binary candidate PG 1302−102, obtained with ESPRESSO at the VLT (R ≃ 138 000). Our methodology, based on robust Bayesian model selection, reveals the presence of multiple narrow emission lines at the expected redshift of the source and confirms (for Hβ) and detects (for Hγ) the clear presence of redshifted broad components. Additionally, we have discovered a “very broad” and, if it is associated with the Hβ, “very redshifted” component at λ ≃ 5000 Å. We evaluate two scenarios for explaining the observed broad emission line (BEL) features in PG 1302−102. In the case in which the redshifted BEL asymmetry arises from the orbital motion of a putative binary, our measurements coupled with simple estimates of the broad-line region (BLR) sizes suggest that the individual black hole BLRs are either settled in a single BLR or in the process of merging and, therefore truncated and highly disturbed. Alternatively, in the scenario of a single SMBH, we explain the distorted emission of the BELs with a nonsymmetric distribution of the BLR clouds; namely, a thin disk with a spiral perturbation. This BLR configuration is statistically preferred over any empirical multi-Gaussian fit and simultaneously explains the asymmetric emission of the Hβ and Hγ close to the bulk of the line and any additional excess (or the lack of it, in the case of the Hγ) at much longer wavelengths. The physical origins of the perturbation are still unclear and a connection with the possible presence of a black hole binary cannot be ruled out. Given the growing evidence from theoretical and observational works demonstrating the common presence of disturbed BLRs in active galactic nuclei, we argue that an origin related to self-gravitating instabilities may be more plausible.

• Booth, Mark; Klaassen, Pamela; Cicone, Claudia; Mroczkowski, Tony; Wedemeyer, Sven & Akiyama, Kazunori [Show all 17 contributors for this article] (2024). The key science drivers for the Atacama Large Aperture Submillimeter Telescope (AtLAST). Proceedings of SPIE, the International Society for Optical Engineering. ISSN 0277-786X. 13102. doi: 10.1117/12.3017058. Full text in Research Archive Show summary

  Sub-mm and mm wavelengths provide a unique view of the Universe, from the gas and dust that fills and surrounds galaxies to the chromosphere of our own Sun. Current single-dish facilities have presented a tantalising view of the brightest (sub-)mm sources, and interferometers have provided the exquisite resolution necessary to analyse the details in small fields, but there are still many open questions that cannot be answered with current facilities: Where are all the baryons? How do structures interact with their environments? What does the time-varying (sub-)mm sky look like? In order to make major advances on these questions and others, what is needed now is a facility capable of rapidly mapping the sky spatially, spectrally, and temporally, which can only be done by a high throughput, single-dish observatory. An extensive design study for this new facility is currently being undertaken. In this paper, we focus on the key science drivers and the requirements they place on the observatory. As a 50m single dish telescope with a 1–2° field of view, the strength of the Atacama Large Aperture Submillimeter Telescope (AtLAST) is in science where a large field of view, highly multiplexed instrumentation and sensitivity to faint large-scale structure is important. AtLAST aims to be a sustainable, upgradeable, multipurpose facility that will deliver orders of magnitude increases in sensitivity and mapping speeds over current and planned telescopes.

• Gallardo, Patricio A.; Puddu, Roberto; Mroczkowski, Tony; Timpe, Martin; Dubois-Dit-Bonclaude, Pierre & Groh, Manuel [Show all 9 contributors for this article] (2024). The optical design concept for the Atacama Large Aperture Submillimeter Telescope (AtLAST). Proceedings of SPIE, the International Society for Optical Engineering. ISSN 0277-786X. 13094. doi: 10.1117/12.3020272. Full text in Research Archive Show summary

  The Atacama Large Aperture Submillimeter Telescope (AtLAST) aims to be the premier next generation large diameter (50-meter) single dish observatory capable of observations across the millimeter/sub-millimeter spectrum, from 30 to 950 GHz. The large primary mirror diameter, the 2-degree field of view and its large 4.7-meter focal surface give AtLAST a high throughput (aperture size times field of view) and grasp (throughput times spectral reach), with the ability to illuminate > O(107) detectors. The optical design concept for AtLAST consists of a numerically optimized two-mirror Ritchey-Chrétien system with an additional flat folding mirror, which enables a quick selection among its planned six instrument positions. We present the optical design concept and discuss the expected optical performance of AtLAST. We then present design concepts that can be implemented in the receiver and instrument optics to correct for astigmatism and mitigate the high degree of curvature of the focal surface in order to recover significant fractions of the geometric field of view at sub-millimeter wavelengths.

• Puddu, Roberto; Gallardo, Patricio A.; Mroczkowski, Tony; Dubois-Dit-Bonclaude, Pierre; Groh, Manuel & Kiselev, Aleksej [Show all 11 contributors for this article] (2024). A physical optics characterization of the beam shape and sidelobe levels for the Atacama Large Aperture Submillimeter Telescope (AtLAST). Proceedings of SPIE, the International Society for Optical Engineering. ISSN 0277-786X. 13094. doi: 10.1117/12.3020773. Full text in Research Archive Show summary

  The Atacama Large Aperture Submillimeter Telescope (AtLAST) is a project undergoing a design study for a large (50 meter) single-dish submm-wavelength Ritchey-Chrétien telescope to be located 5050 meters above sea level in the Atacama Desert in northern Chile. It will allow for observations covering a wide range of frequencies, from 30 to 950GHz. Observing at such high frequencies with a 50m primary mirror will be challenging, and has never been attempted thus far. This observational capability demands exquisite control of systematics to ensure a high level of directivity and reliable beam shape, and to mitigate the expected sidelobe levels. Among them, critical issues that large telescopes like AtLAST need to deal with are introduced by the panel gap pattern, the secondary mirror supporting struts, mirror deformations produced by thermal and gravitational effects, and Ruze scattering due to surface roughness. Proprietary software such as TICRA-Tools™ allows for full-wave, complex-field simulations of large optical systems taking into account these features. The simulations are performed in a time-reverse sense starting from a Gaussian feed placed at the focus, and computing the surface currents induced by incoming radiation upon each reflector, which acts as well as the source illuminating the subsequent mirror, up to the far field; this approach is known as physical optics. Such calculations can be computationally expensive since the mirror surfaces are gridded (meshed) into a fine array in which each element is treated as a current source. If the telescope size is large and the wavelengths are short this may lead to very long running times. Here we present a set of physical optics results that allow us to estimate the performance of the telescope in terms of beam shape, directivity, sidelobes level and stray light. We also discuss how we addressed the computational challenges, and provide caveats on how to shorten the run times. Above all, we conclude that the scattering effects from the gaps and tertiary support structure are minimal, and subdominant to the Ruze scattering.

• Reichert, Matthias; Timpe, Martin; Kaercher, Hans; Mroczkowski, Tony; Groh, Manuel & Kiselev, Aleksej [Show all 10 contributors for this article] (2024). Technical requirements flow-down for the concept design of the novel 50-meter Atacama Large Aperture Submm Telescope (AtLAST). Proceedings of SPIE, the International Society for Optical Engineering. ISSN 0277-786X. 13094. doi: 10.1117/12.3018133. Full text in Research Archive Show summary

  The Atacama Large Aperture Submm Telescope (AtLAST) is a concept for a novel 50-meter class single-dish telescope operating at sub-millimeter and millimeter wavelengths (30-950 GHz). The telescope will provide an unprecedentedly wide field of view (FoV) of 1-2 degree diameter with a large receiver cabin housing six major instruments in Nasmyth and Cassegrain positions. The high observing frequencies, combined with the scanning operation movements with up to 3deg/second, place high demands on the accuracy and stability of the optical and structural components. The design features the introduction of a rocking chair type mount with an isostatically decoupled main reflector backup structure and an active main reflector surface with a high precision metrology system. The planned site location is in the Chilean Atacama Desert at approximately 5050 meters above sea level, near Llano de Chajnantor. This paper gives an overview of the optical, structural, and mechanical design concepts. It explains the flow-down from key science requirements to technical design decisions as well as showing design analogies from other existing large radio, (sub-)mm, and optical telescopes.

• Travascio, A.; Piconcelli, E.; Bischetti, M.; Cresci, G.; Feruglio, C. & Perna, M. [Show all 26 contributors for this article] (2024). MUSE view of PDS 456: Kiloparsec-scale wind, extended ionized gas, and close environment. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 686. doi: 10.1051/0004-6361/202449201. Full text in Research Archive Show summary

  PDS 456 is the most luminous (Lbol ∼ 1047 erg s−1) radio-quiet quasar at z < 0.3 and can be regarded as a local counterpart of the powerful quasars shining at Cosmic Noon. It hosts a strong nuclear X-ray ultra-fast (∼0.3c) outflow, and a massive and clumpy CO (3–2) molecular outflow extending up to ∼5 kpc from the nucleus. We analyzed the first MUSE Wide Field Mode (WFM) and Adaptive-Optics Narrow Field Mode (AO-NFM) optical integral field spectroscopic observations of PDS456. The AO-NFM observations provide an unprecedented spatial resolution, reaching up to ∼280 pc. Our findings reveal a complex circumgalactic medium around PDS 456, extending to a maximum projected size of ≈46 kpc. This includes a reservoir of gas with a mass of ∼107 − 108 M⊙, along with eight companion galaxies and a multi-phase outflow. WFM and NFM MUSE data reveal an outflow on a large scale (≈12 kpc from the quasar) in [O III], and on smaller scales (within 3 kpc) with higher resolution (about 280 pc) in Hα, respectively. The [O III] outflow mass rate is 2.3 ± 0.2 M⊙ yr−1 which is significantly lower than those typically found in other luminous quasars. Remarkably, the Hα outflow shows a similar scale, morphology, and kinematics to the CO (3–2) molecular outflow, with the latter dominating in terms of kinetic energy and mass outflow rate by two and one orders of magnitude, respectively. Our results therefore indicate that mergers, powerful active galactic nucleus (AGN) activity, and feedback through AGN-driven winds collectively contribute to shaping the host galaxy evolution of PDS 456, and likely that of similar objects at the brightest end of the AGN luminosity function across all redshifts. Moreover, the finding that the momentum boost of the total outflow deviates from the expected energy-conserving expansion for large-scale outflows highlights the need of novel AGN-driven outflow models to comprehensively interpret these phenomena.

• Pensabene, A.; Cantalupo, S.; Cicone, Claudia; Decarli, R.; Galbiati, M. & Ginolfi, M. [Show all 15 contributors for this article] (2024). ALMA survey of a massive node of the Cosmic Web at z ∼ 3: I. Discovery of a large overdensity of CO emitters. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 684. doi: 10.1051/0004-6361/202348659. Full text in Research Archive Show summary

  Submillimeter surveys toward overdense regions in the early Universe are essential for uncovering the obscured star formation and the cold gas content of assembling galaxies within massive dark matter halos. In this work, we present deep ALMA mosaic observations covering an area of ∼2′×2′ around MUSE Quasar Nebula 01 (MQN01), one of the largest and brightest Ly-α emitting nebulae discovered thus far; it surrounds a radio-quiet quasar at z ≃ 3.25. Our observations target the 1.2 and the 3 mm dust continuum as well as the carbon monoxide CO(4–3) transition in galaxies in the vicinity of the quasar. We identify a robust sample of 11 CO-line-emitting galaxies (including a closely separated quasar companion) that lie within ±4000 km s−1 of the quasar systemic redshift. A fraction of these objects were missed in previous deep rest-frame optical/UV surveys, which highlights the critical role of (sub)millimeter imaging. We also detect a total of 11 sources revealed in the dust continuum at 1.2 mm; six of them have either high-fidelity spectroscopic redshift information from rest-frame UV metal absorptions or the CO(4–3) line that places them in the same narrow redshift range. A comparison of the CO luminosity function and 1.2 mm number count density with those of the general fields points to a galaxy overdensity of δ > 10. We find evidence of a systematic flattening at the bright end of the CO luminosity function with respect to the trend measured in blank fields. Our findings reveal that galaxies in dense regions at z ∼ 3 are more massive and significantly richer in molecular gas than galaxies in fields, which enables a faster and accelerated assembly. This is the first in a series of studies aimed at characterizing one of the densest regions of the Universe found so far at z > 3.

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