High Energy Astrophysical Phenomena
Evidence for Millihertz Oscillations in the bright atoll source GX 3+1
Malu Sudha, Renee M. Ludlam, Diego Altamirano et al. (+2 more)
We report evidence for millihertz (mHz) QPOs in the bright atoll
neutron star low-mass X-ray binary (NS LMXB) source GX 3+1 using NICER in the 0.5–10 keV energy band. Across 7 observational
datasets obtained over 6 days, we made 8 candidate mHz QPO detections with local significance above 95%, one of which remains above 95% global significance after the trial correction. These mHz QPOs were detected in the 7–15 mHz frequency range and had fractional rms amplitudes ranging from 0.51–1.41%. Our studies indicate no association between the hardness intensity diagram location of the candidate QPOs and their rms amplitudes. There appears to be a monotonous increase in rms with energy, except in some observations where there is a pivot around 3–4 keV or at ~ 5 keV. Previous studies of mHz QPOs in other sources in literature indicate a pivot around 3 keV in the rms-energy relation, but in our study some tentative detections suggest a pivot at around ~ 5 keV, though the large uncertainties in most cases prevent a robust statistical claim. Although properties such as the frequency range of detection and fractional rms amplitudes of the mHz QPOs in our study are well in agreement with that in literature for other NS LMXBs, the luminosity at which these candidate QPOs occur are higher than that of other sources. The rms-energy relation of the candidate mHz QPOs and the luminosity at which they occur challenges some of the existing considerations of mHz QPO origin.
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All authors Malu Sudha, Renee M. Ludlam, Diego Altamirano, Edward M. Cackett, Mason Ng
Instrumentation and Methods for Astrophysics
Test Management and Coordination During the Vera C. Rubin Observatory Commissioning and Early Operations Using Zephyr Scale
Bruno Quint, Tiago Ribeiro, Erik Dennihy et al. (+3 more)
The commissioning of the NSF-DOE Vera C. Rubin Observatory required coordinating the planning, design, and execution of hundreds of integration and on-sky tests involving different subsystems and geographically distributed teams. To support this task, we adopted a Jira-native test management tool, Zephyr Scale. The initial use of Zephyr Scale focused solely on system verification and validation. Its use was rescoped to coordinate higher-level tests, and it is still in use in early operations. Zephyr Scale allows the creation of Test Cases, which represent individual tests. Each Test Case contains the information needed to execute a test at the summit. This includes a step-by-step script. Every day, Test Cases are grouped into a Test Cycle, which represents the test plan for all tests to be executed that day and that same night. We describe the defined workflow for test creation, review, and deployment, which bridges the gap between ideation and on-sky execution within a Test Cycle. We also outline how we write more complex tests as partially automated JSON files consumed by the Scheduler–the system's real-time, constraint-aware observation optimization engine. This integration enables the Scheduler to ingest high-level observing scripts that communicate with subsystems via an abstraction layer to execute common observatory operations, such as slewing, tracking, and data acquisition. Finally, we summarize the benefits and limitations of using Zephyr Scale, designed initially to coordinate software testing, for large-scale observatory commissioning and early operations.
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All authors Bruno Quint, Tiago Ribeiro, Erik Dennihy, Brian Stalder, David Sanmartim, Keith Bechtol
Instrumentation and Methods for Astrophysics
Modeling of the diffuse background produced by the Vera C. Rubin Observatory M2 baffle scattered light
Alessio Taranto, Gabriele Rodeghiero, Luca Rosignoli et al. (+58 more)
The Vera C. Rubin Observatory, with its unprecedented field of view and fast focal ratio, will survey the entire sky every 3.5 nights. This unique capacity requires dealing with off axis light that can produce stray light artefacts on the images. The secondary mirror (M2) baffle restricts the light that reaches the LSSTCam detector and it contributes to shaping the inner edge of the
telescope optical pupil. This work studies the contribution to the background from the light scattered by the M2 baffle itself. The evanescence of this feature, together with the challenge of isolating it from the sky background, led to the necessity of performing in dome tests using a Collimated Beam Projector (CBP), normally used for calibration purposes. To complete the analysis, in addition to the in dome tests, an on sky observational campaign was conducted. This campaign employed both
stellar targets and the Moon as illumination sources in order to determine the actual energy associated with the feature. The test data have been retro fitted thanks to the combination of ray tracing simulation, CBP and on sky data to infer the intensity and spatial distribution of the background scattered light within the different LSSTCam filters. We quantified the on sky impact of scattered light from the M2 baffle, both for light coming from bright and red
stars and from the Moon. We also developed an approximate relation to transform the in dome measurements into predictions of on sky behavior. This transformation was achieved by comparing the illumination footprint produced by an off axis
star with that generated by the CBP and by mapping the
stellar Spectral Energy Distribution (SED) onto the CBP's set of discrete wavelengths. Finally, we extrapolated the scattered light behavior of the Moon to
stellar sources, in order to build a compplete description of the M2 baffle contribution over the full range of magnitudes.
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All authors Alessio Taranto, Gabriele Rodeghiero, Luca Rosignoli, Aashay Pai, Alex Drlica Wagner, Elana K. Urbach, Fritz Muller, Eli S. Rykoff, Hannah M.M.Pollek, John Andrew, Douglas R. Neill, Parker Fragelius, Tomislav Vucina, Christopher W. Stubbs, Robert H. Lupton, Lee S. Kelvin, Kate Napier, Jacqueline Seron Navarrete, Travis Lange, Andrew P. Rasmussen, Aaron Roodman, Chuck F. Claver, Joshua E. Meyers, Anastasia Alexov, Keith Bechtol, Brian Stalder, R. Lynne Jones, Leanne P. Guy, Tiago Ribeiro, Erik Dennihy, Bruno C. Quint, Aaron E. Watkins, Alysha B. Shugart, Lukas Eisert, Kevin Fanning, Marina S. Pavlovich, Yijung Kang, Hye Yun Park, Paulo Lago, Kris Mortensen, Paulina Venegas Salas, Minhee Hyun, Karla Pena Ramirez, David Sanmartim, Qianjun Hang, Gonzalo Aravena, Kshitija Kelkar, Carlos A. L. Morales Marin, Danica Zilkova, Eric J. Christensen, Yusra Alsayyad, William O'Mullane, Enrico Giro, Rodolfo Canestrari, Sandrine J. Thomas, Kevin A. Reil, Claudio H. Araya Cortes, Roberto Tighe, Holger Drass, Pablo Zorzi, Massimo Brescia
Instrumentation and Methods for Astrophysics
Laser-based metrology systems vs wavefront sensing techniques: a comparative overview between the Large Binocular Telescope and the Vera C. Rubin Observatory for the telescope alignment and collimation tracking
Luca Rosignoli, Gabriele Rodeghiero, Sandrine J. Thomas et al. (+26 more)
This work presents a comparative overview of the collimation and
alignment strategies employed by two leading 8m-class facilities: the Large Binocular
Telescope (LBT) and the Vera C. Rubin Observatory. While both
telescopes share a challenging fast f-number of approximately f/1.2 (considering the LBT in its
Prime Focus configuration), they have adopted reciprocal architectures for the initial optical
alignment strategy and for maintaining collimation during the night. As an initial
alignment strategy, the LBT relies on a Wavefront Sensing technique called Focal Plane Image Analysis. Conversely, the Vera C. Rubin Observatory baseline foresees the usage of a
Laser Tracker system to establish the initial optical states. The strategies for preserving the optical
alignment and maintaining the collimation against gravitational flexure and thermal drift during observations are instead reversed. Besides the use of open-loop corrections based on Look-Up Tables, common on both
telescopes, the LBT utilizes a
laser-based
Telescope Metrology System to monitor the relative position of optics in real-time, applying the corrections between the exposures. In contrast, the Rubin Observatory employs a
Curvature Wavefront Sensing technique, using dedicated detectors at the four corners of the focal plane. Rather than identifying a best strategy, this work aims to synthesize the strengths, limitations, and operational trade-offs of these complementary approaches, from the perspective of the next generation of Extremely Large
Telescopes and their instruments.
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All authors Luca Rosignoli, Gabriele Rodeghiero, Sandrine J. Thomas, Guillem Megias Homar, Heejoo Choi, John Hill, Olga Kuhn, Elena Masciadri, Byeongjoon Jeong, Brandon Mechtley, Christian Veillet, Elana Urbach, Brian Stalder, Jason Chu, Alessio Taranto, J. Bryce Kalmbach, Joshua E. Meyers, Andrew J. Connolly, Rebekah Polen, John Franklin Crenshaw, Krzysztof Suberlak, Tiago Ribeiro, Roberto Tighe, Merlin Fisher-Levine, Mario Rivera, Enrico Giro, Rodolfo Canestrari, Holger Drass, Pablo Zorzi Massimo Brescia
Instrumentation and Methods for Astrophysics
Setting requirements on out-of-band rejection for next-generation CMB experiments. Application to the LiteBIRD instrument
L. Mousset, L. Montier, J. Aumont et al. (+15 more)
Next-generation
cosmic microwave background experiments have very stringent constraints to achieve the required sensitivity to target polarization $B$ modes. In this work, we intend to set requirements on the out-of-band rejection level, with out-of-band referring to frequencies outside the
telescope band-pass. The method developed is applied to the LiteBIRD Medium and High Frequency
Telescopes. In order to determine the impact of out-of-band power, we model the instrument's optical response and the spectral emissions of the sky and of the instrument itself. This allows us to propagate optical power inside the
telescope. Using this tool, we address both the impact of out-of-band power on the detection chain and on the thermal heat load, together with the impact on the process of separation between astrophysical components. The role of additional static power as well as dynamic power variations is studied. The requirement derived consist in attenuation factors (in dB) in frequency subdomains. They will be used to design the
telescope filters.
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All authors L. Mousset, L. Montier, J. Aumont, F. Columbro, P. de Bernardis, J. Errard, C. Franceschet, S. Giardiello, T. Ghigna, H. Hubmayr, G. Jaehnig, S. Masi, F. Piacentini, G. Pisano, A. Rizzieri, G. Savini, C. Tucker, LiteBIRD Collaboration
Astrophysics of Galaxies
Uncovering neutral Hydrogen clouds in Radio Galaxies in the SKA era
Mamta Pandey-Pommier
AGN feedback driven by
radio jets plays a key role in regulating the cold ISM of
galaxies. Neutral hydrogen traced through the H1 21-cm line provides a powerful probe of the kinematics, distribution, and physical conditions of cold gas in the central regions of AGN. Previous observations have detected H1 column densities down to $\sim10^{20}$ cm$^{-2}$, but typically at arcsecond-scale resolution, inhibiting the characterization of small-scale H1 gas clouds and their connection to molecular gas reservoirs and sites of jet-ISM interaction. High-resolution H1 imaging is therefore required to determine whether the atomic gas is associated with circumnuclear structures, jet-driven
outflows, compressed gas layers, or fragmented cold clouds embedded within a disturbed multiphase ISM. In this chapter, we focus on molecular gas-rich
radio AGN hosting large-scale jets and exhibiting strong interactions between the
radio plasma and the surrounding ISM, where atomic, molecular, and ionized gas coexist. These systems provide ideal laboratories for investigating the spatial distribution and kinematics of H1, constraining the impact of
radio jets on the cold gas, and determining whether the gas is associated with inflowing, outflowing, or otherwise disturbed components. SKA-VLBI will deliver milliarcsecond-scale imaging and $\mu$Jy-level sensitivity, resolving H1 gas clouds on parsec scales across extended
radio structures. This capability will enable detailed constraints on the location, morphology, and kinematics of atomic gas from the
nuclear regions to kiloparsec-scale jet-ISM interaction sites. Combined with molecular gas observations at other wavelengths, these measurements will provide a comprehensive view of the jet-ISM interactions, the impact of AGN-driven feedback, and the role of cold gas in
galaxy evolution.
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High Energy Astrophysical Phenomena
The location of the upper edge of the pair-instability supernovae black hole mass gap
Jeremy Sakstein and Djuna Croon
Gravitational wave observations are beginning to probe the upper edge of the pair-instability
supernova (PISN) black hole mass gap, a key prediction of
stellar evolution. In this work, we quantify the sensitivity of this boundary to uncertainties in
stellar evolution using a suite of simulations that vary inputs including
nuclear reaction rates, mixing processes, and
stellar winds. We find that the $^{12}{\rm C}(\alpha,\gamma)^{16}{\rm O}$ reaction rate is the dominant source of uncertainty, shifting the upper edge by $\Delta M\sim30\,{\rm M}_\odot$, with the triple-$\alpha$ rate producing a comparable shift of $\sim25\,{\rm M}_\odot$. Notably, $^{16}{\rm O}+^{16}{\rm O}$ reactions shift the upper edge by $\sim15\,{\rm M}_\odot$ while leaving the lower edge unchanged, implying they can widen or narrow the mass gap. Other processes affect the location at the $\lesssim10\,{\rm M}_\odot$ level. In contrast to the lower edge, we find that the upper edge is robust to variations in spatial and temporal resolution, indicating that it is reliably resolved in current simulations. Our results demonstrate that the upper edge carries substantial theoretical uncertainty and, while comparatively less affected by astrophysical contamination than the lower edge, provides a direct probe of the
nuclear processes governing pair instability. We discuss the implications for interpreting high-mass black hole detections in gravitational wave data.
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Earth and Planetary Astrophysics
Search for L4 Earth Trojan asteroids with the 2.5-meter Wide Field Survey Telescope
Junqiang Lu, Lulu Fan, Shaohan Wang et al. (+16 more)
Earth Trojan asteroids (ETAs) are a mysterious population, and dynamically stable ETAs, if
primordial, could be "living fossils" of the early
solar system. To date, there are only two known ETAs, but both are temporary ETAs. The aim of our survey is to discover new temporary or stable ETAs; in the absence of detections, we derive upper limits on the population of stable ETAs. We conducted the largest wide-area survey of the Earth's L4 Lagrange point region so far using the Wide Field Survey
Telescope, covering about 236.74 deg^2, corresponding to 33.24% of the probability coverage for sky regions where dynamically stable L4 ETAs are likely to reside. No new ETAs were detected in our survey. We place a cumulative upper limit of N(H < 19.1) < 19 on the stable population of objects larger than ~520 m (for an assumed albedo of 0.15). This represents the most stringent constraint on the ETA population to date.
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All authors Junqiang Lu, Lulu Fan, Shaohan Wang, Minxuan Cai, Bingxue Fu, Xu Kong, Haibin Zhao, Bin Li, Qingfeng Zhu, Zhen Wan, Feng Li, Ming Liang, Binyang Liu, Zheng Lou, Jinlong Tang, Hairen Wang, Jian Wang, Yongquan Xue, Hongfei Zhang
Solar and Stellar Astrophysics
The CepA disk-outflow system at <=0.2” or <=100au resolution
H. Beuther, C. Gieser, V. Aberham et al. (+21 more)
Context: Although there has been significant progress, the physical properties and potential fragmentation of
accretion disks around high-mass protostars remain poorly constrained. Aims: We characterize at high angular resolution one of the most nearby (~700pc) high-mass
accretion disk candidates CepA HW2. Methods: Using the new long baseline array configuration (~1700m) of the Northern Extended Millimeter Array (NOEMA), we study CepA HW2 with a resolution of <=0.2” or <=100au at 1.3mm in
dust continuum and spectral line emission. Results: The mm continuum emission resolves the central disk candidate into several sub-structures. Conducting a Toomre Q stability analysis based on CH_3CN and continuum data, and a comparison to 3D radiation hydrodynamic simulations shows that the data are consistent with an almost edge-on disk where the observed sub-structures may represent fragments within the disk. The CO and SiO spectral line data confirm a second bipolar
outflow (in addition to the well-known jet) emanating from the central peak position. This indicates that this central peak should host at least a binary if not even a higher order multiple system. The usually assumed dense gas tracer CH_3CN shows also contributions from the
outflows which complicates further kinematic analysis of the disk. Conclusions: The high-resolution
outflow-disk data of CepA reveal a multiply fragmented disk that drives several
outflows. These observations enforce the picture of high-mass
star formation where multiplicity and fragmentation can happen on the smallest spatial scales related to the inner
accretion disks.
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All authors H. Beuther, C. Gieser, V. Aberham, J.M. Winters, R. Neri, A. Ahmadi, R. Kuiper, Th. Henning, H. Linz, T. Möller, V. Elbakyan, L. Moscadelli, D. Semenov, J. Urquhart, P. Klaassen, M. Beltran, Á. Sánchez-Monge, T. Peters, R. Galvan-Madrid, S. Leurini, S. Lumsden, R.E. Pudritz, A. Palau, H. Zinnecker
Instrumentation and Methods for Astrophysics
Focal Plate Prototyping for Modular Focal Planes of Stage-5 Instruments For Ground-Based Telescopes
Maxime Rombach, Jean-David Perriard, Laurent Chevalley et al. (+3 more)
As current Stage-4 multi-object instruments such as SDSS-V, DESI, MOONS or 4MOST are providing astrophysicists data to study the objects of the Universe, effort is arising to build the next generation of Stage-5 multi-object focal planes; aiming for 20'000 fibers-class instruments. The focal plate structure is a central element of the future focal plane assemblies. It maintains the fiber positioners, the Guide, Focus and
Alignment cameras (GFAs) and wave-front sensors together on the focal surface of the
telescope. In addition to being optimized for stiffness and mass, the plate needs to meet tight tolerances in tilt, typically pm 0.05 degres, and focus, typically, pm 30 um, to match the
telescope's curved focal surface. The presented focal plate prototype shows that 5-axes machining is promising to meet the desired tolerances.
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All authors Maxime Rombach, Jean-David Perriard, Laurent Chevalley, Diane Chapuis, Markus Thurneysen, Jean-Paul Kneib
Instrumentation and Methods for Astrophysics
Robust CMB polarisation mapmaking with a rotating half-wave plate
Wuhyun Sohn, Simon Biquard, Josquin Errard et al. (+1 more)
We present a novel mapmaking method for obtaining unbiased estimates of CMB polarisation, tailored to modern CMB experiments with a rotating half-wave plate. These experiments are exposed to strong unpolarised contaminant sources, such as atmospheric emission and ground pickup, which can be several orders of magnitude stronger than the sky signal. Our mapmaker mitigates these systematic effects by marginalising over all signals that vary slowly compared to the timescale of a polarimeter's angle rotation on the sky, while recovering high-fidelity polarisation maps. When the variability timescales of the unpolarised signals exceed a quarter of the half-wave plate rotation period, the method can produce maps with nearly optimal noise levels and minimal contamination. Furthermore, if the half-wave plate rotation period is sufficiently short relative to the beam-scale crossing time, the method efficiently mitigates the sky intensity-to-polarisation leakage. This mapmaker, named the Polarisation-Optimised Map-Making
Estimator (POMME), is implemented within the open-source FURAX package and is ready for application to upcoming ground-based CMB surveys.
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All authors Wuhyun Sohn, Simon Biquard, Josquin Errard, Radek Stompor
Astrophysics of Galaxies
Chemo-dynamical Analysis of Eight UBC Open Clusters
Remziye Canbay, Deniz Cennet Ç{\i}nar, Özcan Çal{\i}şkan et al. (+4 more)
We present a comprehensive chemo-dynamical analysis of eight open clusters selected from the UBC catalog using
Gaia DR3 data. These clusters are located at heliocentric distances of ~2-5 kpc, probing regions of the
Galactic disk beyond the
solar neighborhood. Cluster membership is determined using the UPMASK
algorithm, while structural parameters are derived from radial density profiles through King model fitting combined with MCMC sampling. Their structural parameters reveal diverse internal configurations, from diffuse to moderately concentrated systems. Fundamental astrophysical parameters (extinction, distance,
metallicity, and age) are obtained via
Bayesian isochrone fitting based on PARSEC models. The clusters span a wide age range (~20 Myr to ~5 Gyr) and show a broad
metallicity distribution (-0.34 <= [Fe/H] (dex) <= +0.25). Orbital analysis based on backward integrations shows that all clusters follow nearly circular orbits (e ~ 0.03-0.09) with low vertical distances from the
Galactic plane (Zmax < 0.4 kpc), confirming their membership in the
Galactic thin disk and dynamically cold kinematics. Comparison between inferred traceback orbital radii and present-day guiding radii indicates modest radial displacements, with Delta R < 0.5 kpc for the UBC sample. These offsets are consistent with mild radial redistribution expected for young, dynamically cold open clusters rather than strong radial migration. The results suggest that radial migration should be considered when interpreting the present-day spatial and chemical distribution of these clusters, although the inferred migration amplitudes remain moderate. Our results demonstrate that relatively distant open clusters can be characterized with high precision using
Gaia DR3 data and that mild radial redistribution should be considered when interpreting the present-day distribution of
stellar populations in the
Galactic disk.
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All authors Remziye Canbay, Deniz Cennet Ç{\i}nar, Özcan Çal{\i}şkan, Burçin Tan{\i}k Öztürk, Seval Taşdemir, Ege Erayd{\i}n, Selçuk Bilir
High Energy Astrophysical Phenomena
Unveiling Radio Transients with SKAO Telescopes
James C.A. Miller-Jones, Kaustubh M. Rajwade, Patrick A. Woudt et al. (+1 more)
Transient astrophysics provides a set of unique laboratories for studying fundamental physics. From the launching of powerful relativistic jets to merging
neutron stars, highly-magnetised compact objects, or
stellar explosions, transients probe the Universe at its most extreme. The SKAO will provide an unrivalled set of capabilities for transient observations on timescales from nanoseconds to decades, opening new discovery space. With its sensitivity, broad spectral coverage, wide field of view, and high survey speed, SKAO will allow us to discover and understand rare events that provide powerful new insights into regimes of high energy density, strong
gravity, and intense
magnetic fields. Complemented by a suite of multi-wavelength and multi-messenger facilities, and supported by a network of smaller existing
radio telescopes and new computational capabilities, SKAO will unveil the most powerful and exotic events in our Universe, addressing some of the key questions in modern astrophysics and cosmology.
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All authors James C.A. Miller-Jones, Kaustubh M. Rajwade, Patrick A. Woudt, Jason W.T. Hessels
Astrophysics of Galaxies
AGN Feedback: The impact of galactic-scale radio jets on the interstellar medium in starbursting obscured AGN
M. Polletta, C.J. Lonsdale, P. Pallavi et al. (+4 more)
A highly
star-forming
galaxy at z ~ 2 hosting an obscured, luminous active
galactic nucleus (AGN) and a relativistic
radio jet sets the stage for a
cosmic crime scene. The victim is
star formation, the suspect is AGN feedback. These systems offer a rare opportunity to catch this process in the act. We propose SHARP@ELT integral-field spectroscopic observations of heavily obscured, luminous AGN with resolved
radio emission to witness the onset of feedback and its impact on the host interstellar medium (ISM). Such objects trace a short-lived (< 10^5 yr) evolutionary phase in which a recent starburst, newly triggered
radio jets, and a deeply embedded AGN coexist. In this phase, feedback is expected to suppress
star formation while clearing the dusty
nuclear regions. Using SHARP/VESPER, we will derive spatially resolved maps of
stellar ages,
star formation rate density, gas density, and ionization state, alongside the kinematics of
stars and ionized gas. By directly comparing these properties with the
radio structures, we will quantify the effects of both jet-driven and radiative feedback on the ISM. Our sample consists of eleven luminous, obscured AGN at 1.5 < z < 2.5 with resolved
radio emission on scales of ~1-15 kpc. Exploiting the VESPER multi-Integral Field Selector capability, we will obtain resolved continuum and emission-line maps for at least 110
galaxies at
cosmic noon, enabling a comprehensive characterization of their environment, multiphase ISM, and
nuclear activity within 55 h of integration time. SHARP will thus reveal AGN feedback at the epoch when it is most effective, providing a decisive step toward understanding its role in
galaxy evolution.
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All authors M. Polletta, C.J. Lonsdale, P. Pallavi, G. Vietri, A.E. Kimball, P. Franzetti, C.J. Lonsdale
Astrophysics of Galaxies
Fueling and feedback mechanisms at the nodes of the cosmic web
M. Polletta, G. De Lucia, A.R. Gallazzi et al. (+1 more)
The environment plays a key role in shaping how
galaxies form and evolve.
Galaxies in dense nodes of the
cosmic web are thought to grow and quench earlier, and faster and become more massive than those in the field. To understand the physical drivers of this environmental effect, we must probe the most crowded regions of the Universe at the epoch when growth was at its peak and the transition to quiescence was triggered, around 10 billion years ago (z ~ 2). This period saw the downturn of the
cosmic star-formation and black-hole
accretion histories, the quenching and morphological transformation of massive
galaxies, and the virialisation of the first clusters. Several processes might be at play:
stellar and AGN feedback, reduced gas
accretion, disk instabilities, morphological quenching, interactions, and ram-pressure stripping. The ELT/SHARP instrument, with its sensitivity, spectral resolution, wavelength coverage, and multiplexing capabilities over a wide field, is ideally suited to study these mechanisms by targeting multiple members of dense structures simultaneously. Cluster and protocluster cores at z ~ 2 span roughly 1 arcmin and host about ten massive (Mstar > 10^10.5 Msun)
galaxies. VESPER can deliver spatially resolved gas and
stellar kinematics, map recent and past
star formation, identify companions, inflows,
outflows, shocks, and AGN activity for the most massive core members. With 80 hr of VESPER time, we can obtain this type of data for about 60
galaxies selected from the densest regions of five clusters at 1.5 < z < 1.7 and five protoclusters at 2 < z < 2.5 spanning the evolutionary phases of maximal growth and rapid decline. Such a sample would permit to trace the
evolution from protoclusters to virialised clusters and identify the environmental processes responsible for their rapid transformations.
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All authors M. Polletta, G. De Lucia, A.R. Gallazzi, C. Mancini
Earth and Planetary Astrophysics · Cross-listed from physics.space-ph
Cometary ion dynamics at a weakly outgassing comet
Victor Steinwand, Peter Stephenson, Zoe Lewis et al. (+3 more)
The ESA/Rosetta mission escorted comet 67P/Churyumov-Gerasimenko for two years, exploring its
plasma environment across diverse outgassing conditions.
Plasma density observations from the Rosetta
Plasma Consortium (RPC) are broadly categorized into two regimes for the ion dynamics, linked to the presence of a diamagnetic cavity at Rosetta's location. With a diamagnetic cavity present, ions detected by Rosetta are accelerated with respect to the neutral coma. Without a diamagnetic cavity present, at lower outgassing, and nearer the
nucleus, ions co-move with the neutrals. We examine the transition between regimes following Rosetta's last detection of the cavity in February 2016. During this transition, global 3D
plasma models of the cometary ionosphere underestimate
plasma densities. To investigate this underestimation, we assess the sensitivity of cometary ion densities to different parameters using a 3D collisional ion test particle model, driven by electromagnetic fields from hybrid modeling. We show that considering cometary electron cooling is necessary to model cometary ion dynamics within 100 km of the surface. Electron temperatures derived from collisional electron modeling affect ion dynamics via the ambipolar electric field, increasing ion number densities. We further show that the cometary electron cooling exobase organizes Rosetta
plasma density observations; different ion dynamics regimes are linked to the position of Rosetta relative to the exobase. These findings demonstrate that Rosetta was below this exobase for much of the post-perihelion period. They justify the absence of ion acceleration in
plasma density assessments and the use of uniform electron-impact ionization frequencies between Rosetta and the surface during post-perihelion.
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All authors Victor Steinwand, Peter Stephenson, Zoe Lewis, Esa Kallio, Arnaud Beth, Marina Galand
Astrophysics of Galaxies
First-star imprints in a metal-poor galaxy overdensity near the end of reionization
Zihao Li, Koki Kakiichi, Lise Christensen et al. (+24 more)
The first generation of
stars, known as Population III (Pop III), formed from
primordial gas consisting solely of hydrogen and helium and is believed to have emerged only a few hundred million years after the Big Bang. Detecting the chemical enrichment of metal-poor circumgalactic gas offers a promising way to trace the enrichment signature of Pop III
stars. Along the sightline to the
quasar SDSS J0100+2802, a metal absorber at $z = 5.945$, showing over-abundant carbon and silicon compared to
solar, has been reported to be consistent with the enrichment pattern of Pop III
stars. With the James Webb Space
Telescope, we report the discovery of an unusually metal-poor
galaxy overdensity of 17 members (mean
metallicity $\approx 3\%$
solar) near this metal absorber, which is $\sim 0.4$ dex more metal-poor than coeval
galaxies in similarly overdense environments. This less chemically evolved system may have provided favorable conditions for preserving the absorption signatures of Pop III enrichment. We infer a minimum dark matter
halo of $\log(M_{\mathrm{h,min}}/M_{\odot})=10.68^{+0.93}_{-1.72}$, supporting late-time Pop III formation at the outskirts of atomic hydrogen cooling
halos. Our findings open a promising observational pathway to identify the chemical imprints of the first
stars and constrain the conditions for their formation.
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All authors Zihao Li, Koki Kakiichi, Lise Christensen, Zheng Cai, Valentina D'Odorico, Jorryt Matthee, Daichi Kashino, Rongmon Bordoloi, Ruari Mackenzie, Trystyn A. M. Berg, Irene Vanni, Stefania Salvadori, Alessandra Venditti, Shiwu Zhang, Sarah E. I. Bosman, Eduardo Bañados, Frederick B. Davies, Xiaohui Fan, Hyunsung D. Jun, Xiangyu Jin, Mingyu Li, Sofía Rojas-Ruiz, Feige Wang, Jinyi Yang, Siwei Zou, Huanian Zhang, Yongda Zhu
Cosmology and Nongalactic Astrophysics
Ultralight dark matter mixed with primordial black holes
Xing-Yu Yang
Dark matter candidates span many orders of magnitude in mass, from ultralight bosonic fields to massive compact objects. In this work, we connect these two extremes by investigating ultralight dark matter (ULDM) mixed with
primordial black holes (PBHs). We study mixed ULDM-PBH
halos by separating the continuum PBH contribution from the shot-noise fluctuation generated by discrete PBHs. The continuum contribution enters the averaged Schrödinger-Poisson background, while the discreteness contribution is treated as a perturbation that induces ULDM eigenmode transitions and
soliton heating. The two contributions have distinct parametric dependencies: continuum effects scale with PBH fraction, whereas discreteness-driven transition rates scale with the product of PBH fraction and individual PBH mass in the perturbative regime. For a fiducial mixed
halo with ULDM particle mass $10^{-22}\,\mathrm{eV}$, virial mass of order $10^{10}\,M_{\odot}$, and PBH fraction $1\%$, the continuum PBH component modifies the background density, gravitational potential, and low-lying ULDM
eigenvalues only at the sub-percent level. Nevertheless, this percent-level continuum PBH contribution produces a tens-of-percent response in the coherent
soliton region, changing the radial mode participation by about $20\%$. For
stellar-mass PBHs, the discrete shot-noise fluctuation induces extremely slow ULDM mode transitions, with the fastest low-lying multiplet transition having a timescale of order $10^9\,\mathrm{Gyr}$ for
solar-mass PBHs. In this regime, the leading PBH effect is the continuum contribution, while discrete PBH shot noise is dynamically negligible on
galactic timescales.
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Astrophysics of Galaxies
A big step forward with SHARP: spatially resolved stellar population properties in passive galaxies at z > 1.5
A. Gargiulo, C. Mancini, F. R. Ditrani et al. (+6 more)
Understanding when and how massive quiescent
galaxies (log(M*/Msun) > 10.5) assembled their
stellar mass and quenched remains a central challenge in
galaxy evolution. Spatially resolved
stellar population measurements at z > 1.5 offer a uniquely powerful avenue to address this problem, as they can provide information on the radial variations in
stellar age,
metallicity, and enrichment histories in passive
galaxies as they first emerge. In this work, we present a feasibility study quantifying the transformative capabilities of the proposed IFU SHARP/VESPER at the ELT for performing such radial mapping of
stellar population gradients in passive
galaxies at 1.5 < z < 3. Using the COSMOS-Web catalogue, we define a realistic population of massive quiescent systems at 1.5 < z < 3 and model representative compact and extended
galaxies across this
redshift range. Through detailed simulations with the official SHARP ETC, we derive the exposure times required to reach S/N = 10-15 per resolution element at key rest-frame optical wavelengths. Our results show that SHARP will routinely measure
stellar population gradients out to 2Re for the majority of the population at z < 2.5 with integrations of about 20h, and that will reach at least Re in about 30h at z = 3. Thanks to MORFEO's MCAO and to its spatial resolution of 30mas SHARP/VESPER will also resolve the inner < 1kpc at all
redshifts considered, enabling for the first time, direct tests of quenching mechanisms linked to central mass build-up, bulge growth, and structural transformation. These findings demonstrate that SHARP/VESPER will open an entirely new observational window on the early
evolution of massive quiescent
galaxies, providing, for the first time, statistically meaningful, spatially resolved
stellar population constraints during the epoch when their
stellar cores were assembled.
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All authors A. Gargiulo, C. Mancini, F. R. Ditrani, S. Bisogni, P. Franzetti, G. Vietri, A. Gallazzi, M. Longhetti, S. Zibetti
Instrumentation and Methods for Astrophysics
Multi-Scale Contrastive Attention for Light-Curve Representation Learning
Torsha Majumder, Konstantin Malanchev and Emille E. O. Ishida
Current and next-generation time-domain surveys demand automated techniques capable of analyzing millions of light curves, observed in multiple filters, without relying on exhaustive human annotation or scarce spectroscopic follow-up. We present Astra-CLR, an
attention-based, self-supervised contrastive learning framework which enables the representation of raw light curves into a highly discriminative latent space. Pre-trained on $\sim$2.1 million unlabeled Zwicky Transient Facility light curves, the framework utilizes partial light curves as input sequences to generate asymmetric, multi-scale temporal views (explicitly contrasting shorter sequences against longer ones) forcing the network to learn a robust "local-to-global" mapping strategy. Furthermore, we introduce a novel multi-view late fusion architecture that extends the model to efficiently handle longer light curves with larger numbers of observations while accommodating the different cadences associated with each filter. The discriminatory power of the resulting representations was evaluated by using them as input to a Multinomial Logistic Regression classifier, trained to identify 12 broad classes of variability. Final accuracy achieved $\sim 0.70$. When applying a label-efficient, partial top-layer fine-tuning strategy, the topological structure of the latent space is significantly refined, boosting results to $\sim$0.77. Astra-CLR is the first publicly available multi-filter time-series
Transformer trained exclusively on real ZTF light curves. Results presented here demonstrate that it provides an ideal foundation for the development of end-to-end pipelines, taking into account color
evolution and respecting the inhomogeneous nature of astronomical light curve sampling.
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Solar and Stellar Astrophysics
Magnetic activity in cool stars: manifestations and relevance to exoplanets
E. Iş{\i}k, A. Valio, A. Strugarek et al. (+10 more)
Understanding
stellar magnetic activity is central to
exoplanet science in two ways: it sets the dynamic astrospheric boundary condition governing planetary space environments, and it is the primary obstacle to
exoplanet detection and characterisation, since magnetically driven variability imprints correlated quasi-periodic signals across detection time series. In cool
stars, MHD-dynamo-generated fields emerge at the photosphere as bipolar regions, drive chromospheric and coronal heating, modulate irradiance and wind, and power
flares and coronal mass ejections. Spatial scales range from individual flux tubes to global coronal configurations, and temporal scales from minutes to decades and beyond, requiring observational and theoretical tools of correspondingly wide scope. We review observational manifestations and physical models of
magnetic activity in
stars with outer convective envelopes, addressed to the
exoplanet community. We develop the
solar-
stellar connection through the 'Sun in Time' framework and a sequence of
solar analogues serving as evolutionary snapshots of a
solar-mass
star over several Gyr. We survey photospheric, chromospheric, and coronal activity diagnostics across timescales, together with forward-modelling tools translating surface field distributions into signals at or above the level of
exoplanet detection. Empirical rotation-activity relationships and their physical interpretation are examined across all three atmospheric layers. Surface reconstruction techniques are assessed for their diagnostic reach and limitations. The
evolution of magnetism in
solar-like
stars is discussed as context for habitability and as a window to other worlds. We close with an account of how
stellar magnetism sculpts the astrospheric environment and affects close-in
exoplanets, followed by a synthesis of outstanding issues and an outlook on future prospects.
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All authors E. Iş{\i}k, A. Valio, A. Strugarek, S. Järvinen, K. Vida, A. Buccino, K. Namekata, T. Hackman, J. Alvarado-Gomez, D. Nandy, A. O. Farrish, K. Poppenhäger, P. Figueira
Astrophysics of Galaxies
Physical and Chemical Conditions of Molecular Gas in NGC 1068: The nuclear feedback in the circumnuclear disk and starburst ring
Bin Jia, Serena Viti, Erica Behrens et al. (+1 more)
Molecular gas in
galaxies is shaped by both
star formation and active
galactic nuclei. In NGC 1068, the circumnuclear disk and the starburst ring offer a nearby case to study these effects with many molecular tracers. Earlier work has shown strong
outflow activity and complex chemistry, which motivates the use of methods that combine radiative transfer with time-dependent chemistry. Our aim is to map the physical conditions across the circumnuclear disk and the starburst ring of NGC 1068 and to test whether the
nuclear outflow influences the molecular gas in the ring. We also examine whether the heating or the quiescent cloud scenario better matches the observations. We use archival ALMA observations obtained in Bands 3, 4, and 5, covering molecular species including HCN, HCO+, HNC, CS, CN and C2H. All data cubes are convolved to a common resolution of 0.8" and are sampled into 56 pc hexagons with a signal-to-noise threshold of three. We perform hierarchical
Bayesian inference that links a non-LTE radiative transfer module SpectralRadex with chemical modelling. To make the analysis efficient, we replace direct UCLCHEM calculations with a neural network emulator trained on a large model grid. Sampling is done with Nautilus. We also compare our results with previous studies that used RADEX and UCLCHEM for selected regions. The emulator reproduces the UCLCHEM abundances with low error and allows inference at modest computational cost. We find clear radial and azimuthal variations in gas density, temperature, column density, and
cosmic-ray ionization rate.
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All authors Bin Jia, Serena Viti, Erica Behrens, Yun-Hao Zhang
Cosmology and Nongalactic Astrophysics
Predisposition of galaxy clusters to producing exotic hyperbolic umbilic lensing configurations
Quentin Basto, Johan Richard, David J. Lagattuta et al. (+2 more)
Strong gravitational
lensing is a powerful tool for investigating the universe's large-scale structure and understanding the properties of dark matter and dark energy. The magnification and distortion of distant background sources by cluster lenses have enabled detailed studies of both lens and source populations, making these systems promising probes for precision cosmology. While classical strong-lenses are well understood, much remains to be explored for
hyperbolic-umbilic (HU) exotic lenses, which produce unique telescopic effects and uncommon images with potentially very high magnifications. Identifying and quantifying these objects, along with characterising their
geometric configurations, could have broad implications for studies of
galaxy clusters and lensed
galaxy populations. Using parametric cluster mass models, we mapped regions in the source plane where HU exotic images can form and integrate these areas over
redshift to define an exotic comoving volume (V_z<10). We validated this approach on confirmed exotic systems (RXJ0437.1+0043 and Abell 1703), then applied it to a sample of 74 cluster models. We show HU-region contours for the most promising clusters, assess both systematic and
stochastic uncertainties on exotic area and volume estimates, and confirm that our error remains sufficiently small to support robust conclusions. Next, we explore correlations between six cluster parameters and (V_z<10), finding that pairs of parameters, especially ellipticity with Einstein radius or cuspiness, best distinguish high-(V_z<10) systems. Finally, we estimate that each cluster contributes ~0.125
galaxies to its exotic volume on average (as a conservative lower bound), meaning that observing 19 clusters yields a 90% chance of detecting at least one HU system in a random sample.
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All authors Quentin Basto, Johan Richard, David J. Lagattuta, Ashish K. Meena, Harald Ebeling
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Nonlinear growth and amplification of phase-transition gravitational waves induced by cosmic expansion
Xiao Wang, Chi Tian and Csaba Balázs
We perform the first three-dimensional hydrodynamical simulations of cosmological first-order phase transitions in an expanding background. These simulations consistently incorporate the effects of the evolving phase transition strength throughout the full nucleation process of slow phase transitions. We find that, in addition to reducing mean bubble separations via an effectively enhanced nucleation rate,
cosmic expansion unexpectedly induces highly nonlinear growth in the gravitational wave energy fraction, ultimately leading to a significant $\mathcal{O}(10)$ to $\mathcal{O}(100)$ amplification of the gravitational wave spectra. This amplification is more pronounced for initially weak transitions than for those of initially intermediate strength. Our results highlight the challenge and importance of accurately modelling slow phase transitions while accounting for
cosmic expansion.
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Astrophysics of Galaxies
Electron Densities of Typical Low-Mass Galaxies at z~2-7 from Stacked JWST/NIRSpec Spectra
Shihong Liu and Yu Rong
Direct electron-density measurements at high
redshift are usually limited to
galaxies with individually strong density-sensitive doublets, and therefore may not trace the average interstellar medium of ordinary low-mass
galaxies. We stack public JWST/NIRSpec medium-resolution spectra from the DAWN JWST Archive to measure [SII]-based electron densities $n_e$ for low-mass
galaxies at $2<z<7$. The stacks yield $n_e\simeq100$–$150\ {\rm cm^{-3}}$ at $2<z<5$ and $n_e=381^{+104}_{-89}\ {\rm cm^{-3}}$ at $5<z<7$, corresponding to an
evolution $n_e=n_{e,0}[(1+z)/(1+2.3)]^\alpha$ with $n_{e,0}=76^{+22}_{-23}\ {\rm cm^{-3}}$ and $\alpha=1.88^{+0.60}_{-0.64}$. A mass-matched stacking test gives a consistent rising trend, indicating that the increase is not driven solely by changing
stellar-mass distributions. Individually measurable
galaxies with both [SII] components detected at ${\rm S/N}>5$ have a higher normalization, $n_{e,0}=211^{+36}_{-31}\ {\rm cm^{-3}}$, showing that individual-doublet samples select a denser subset. Stacking archival JWST spectra therefore provides a direct route to measuring the average gas density of low-mass
galaxies below the individual-doublet detection threshold.
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Astrophysics of Galaxies
Tracing Cold Gas in Absorption Across Cosmic Time with the SKA
Elizabeth K. Mahony, Neeraj Gupta, Sergei A. Balashev et al. (+12 more)
Observing the 21-cm HI line in absorption provides a powerful means of tracing the cold neutral gas in normal and active
galaxies across
cosmic time. The frequency coverage and sensitivity of SKAO will allow us to detect HI in absorption from z = 0 to beyond z = 6, enabling the characterisation of the properties of cold gas in and around
galaxies at all epochs. This chapter summarises recent advances in absorption-line studies, lessons learned from precursor surveys, and updates the science case presented in Kanekar and Briggs (2004) and Morganti et al. (2015), focusing on the capabilities enabled by the SKA design baseline, Array Assembly 4 (AA4). We expand on these earlier works by presenting new opportunities to simultaneously search for OH 18-cm absorption, an efficient tracer of diffuse molecular gas that complements the atomic gas traced by HI absorption, as well as the need for sub-arcsecond scale spectroscopic imaging and multi-wavelength data from large surveys. These advances will allow SKAO absorption surveys to address key questions surrounding the fuelling and feedback cycles of AGN and the
evolution of the cold neutral gas across
cosmic time.
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All authors Elizabeth K. Mahony, Neeraj Gupta, Sergei A. Balashev, Yogesh Chandola, Francoise Combes, Rebecca Davies, Jens-Kristian Krogager, Wenkai Hu, Filippo M. Maccagni, Pasquier Noterdaeme, Mamta Pandey-Pommier, Elaine M. Sadler, Rasha M. Samir, Nick Seymour, Hyein Yoon
Astrophysics of Galaxies
The FAST All Sky HI Survey DR2: the FASHI Catalog and the HI Mass Function
Chuan-Peng Zhang, Ming Zhu, Peng Jiang et al. (+8 more)
The FAST All Sky HI Survey (FASHI) conducted with the Five-hundred-meter Aperture Spherical
radio Telescope (FAST) has mapped $\sim 19500\,\mathrm{deg}^2$ of the sky north of DEC $= -14^{\circ}$, detecting $156411$ extragalactic HI sources at $z< 0.09$ with a median sensitivity of $0.57\,\mathrm{mJy}\,\mathrm{beam}^{-1}$ at a velocity resolution of $6.4\,\mathrm{km}\,\mathrm{s}^{-1}$. The survey achieves unprecedented depth and area coverage, significantly improving upon previous single-dish surveys. Through a detailed completeness analysis that accounts for the survey's non-uniform sensitivity and line-width dependence, we construct a robust HI mass function (HIMF) using a completeness-corrected sample of over $109000$ sources. The HIMF is robustly constrained down to $M_{\mathrm{HI}}\sim 10^{6.2}\,M_{\odot}$. When systematic uncertainties are included, the HIMF is well described by a single-Schechter function with a characteristic mass $\log (M_{*} / h_{70}^{-2}M_{\odot}) = 9.89\pm 0.02$, low-mass end slope $\alpha = -1.31\pm 0.02$, and amplitude $\phi_{*} = (6.38\pm 0.49)\times 10^{-3}\,h_{70}^{3}\,\mathrm{Mpc}^{-3}\,\mathrm{dex}^{-1}$. The derived
cosmic HI density is $\Omega_{\mathrm{HI}} = (4.71\pm 0.03_{\mathrm{stat}}\pm 0.40_{\mathrm{sys}})\times 10^{-4}\,h_{70}^{-1}$. FASHI provides the most extensive and sensitive HI catalog to date, establishing an important
benchmark for studies of gas
accretion,
galaxy evolution, and large-scale structure in the local universe.
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All authors Chuan-Peng Zhang, Ming Zhu, Peng Jiang, Hong Guo, Jin-Long Xu, Xiao-Lan Liu, Nai-Ping Yu, Cheng Cheng, Jing Wang, Jie Wang, FAST Collaboration
Astrophysics of Galaxies
A generalized linear matrix method for normal modes in collisionless stellar disks
Evgeny V. Polyachenko and Ilia G. Shukhman
We generalize the linear
matrix method for computing normal modes in collisionless
stellar disks to distribution functions with sharp edges at zero angular momentum ($L=0$). The generalization adds boundary-integral terms to the
matrix equation without increasing its size. We validate the method by computing $m=2$ modes for two Kuzmin–Toomre disk models (Miyamoto $n_{\rm M}=3$ and Kalnajs $m_{\rm K}=6$ families) and comparing the
eigenvalues with those obtained from an independent nonlinear
matrix method based on logarithmic-spiral expansions. A systematic convergence study over grid resolution and harmonic truncation yields
eigenvalues accurate to ${\sim}\,0.003$ in both pattern speed and growth rate. Unlike the nonlinear method, the linear method naturally incorporates gravitational softening, enabling the computation of eigenmodes for softened disk models. The implementation in Julia with GPU acceleration is openly available.
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Solar and Stellar Astrophysics
State-of-the-art Observation, Calibration, and Imaging Framework for Solar and Heliospheric Sciences with SKA
Divya Oberoi, Devojyoti Kansabanik, Soham Dey et al. (+6 more)
The Sun is a surprisingly difficult
radio source to observe and image, even with the SKA. It is multiple orders brighter than the typical
radio sources, which sensitive
radio telescopes like SKA are optimized for. So, configuring the signal chain to enable
solar observations while maintaining linearity is the very first non-standard requirement to be met. Next,
solar radio emission spans an impressive range along every single phase-space parameter that can be used to describe it – time scales from
solar cycles to millisecond; spectral scales from smooth thermal emission to $\sim$100 kHz coherent emission; brightness temperatures from $10^4$ K for gyrosynchrotron emissions to $10^{13}$ K for bright type-III bursts; fractional polarizations from less than 1% to nearly 100%; and angular scales extending beyond a degree. Capturing the dynamics in
solar radio emission in their full glory requires, on the one hand, that all the data that goes into making an image be acquired over very short temporal and spectral spans and, on the other, also imposes requirements for very high imaging dynamic range with high polarization purity. Extracting the information at the requisite temporal and spectral scales from SKA data will require a spectropolarimetric snapshot capability with high dynamic range and fidelity. Additionally, some of the most interesting insights into
solar physics and space weather come from studying
solar activity, which remains inherently unpredictable. This chapter discusses the various considerations that need to be addressed to help realize the promise of
solar and heliospheric science from SKA.
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All authors Divya Oberoi, Devojyoti Kansabanik, Soham Dey, Puja Majee, Surajit Mondal, Deepan Patra, Jingye Yan, Peijin Zhang, Pietro Zucca
Astrophysics of Galaxies
The metallicities of little red dot host galaxies: LRDs are metal poor, but not pristine
G.P. Nikopoulos, D. Watson, C.L. Pollock et al. (+4 more)
Little Red Dots (LRDs) are a population of high-z sources discovered by JWST whose compactness, broad permitted lines, strong absorption features, continuum shapes and luminosities point to accreting supermassive black holes (SMBHs) embedded in dense gas. To date, the
metallicity of the hosts of these systems has not been systematically measured. We determine the gas-phase
metallicities of LRD host
galaxies and test whether their narrow-line emission is consistent with metal poor
star formation or AGN activity. We assemble a sample of 24 LRDs at z ~ 2.3-7 with medium and high-resolution JWST/NIRSpec data. We derive oxygen abundances and electron temperatures using the direct Te method applied exclusively to the narrow components of emission lines, and cross-check against widely used strong line calibrations. We derive a sample-averaged abundance of $Z_{T_\mathrm{e}} = 0.08_{-0.03}^{+0.11}\,\mathrm{Z_{\odot}}$ ($T_\mathrm{e} = 23000_{-7000}^{+17000}$\,K), placing LRDs firmly in the metal-poor regime of high
redshift star forming
galaxies. The R-hat calibration yields a consistent average of $Z_{\hat{\mathrm{R}}} = 0.07_{-0.04}^{+0.07}\,\mathrm{Z_{\odot}}$, with only 4% scatter relative to the direct Te method, providing a robust proxy for systems where the [O III]4363Å line is not detected. We also identify two extremely metal-poor LRDs with
metallicities <1.3%. The general population of LRDs are among the lower
metallicity galaxies found by JWST at this epoch; they exhibit a narrow range of
metallicities with a range of about 0.6 dex, which remains remarkably stable over
cosmic time. Such low
metallicity may then be a defining property of the class. The fact that LRDs have substantial
metallicity across most of the class poses a challenge to models that require formation via pristine gas collapse, while their generally low
metallicity indicates that they are not standard AGN.
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All authors G.P. Nikopoulos, D. Watson, C.L. Pollock, A. Sneppen, K. E. Heintz, J. Witstok, G. Brammer