arXiv subjects

Caitlin Casey

Publications and source records attributed to Caitlin Casey.

At least 19 recordsLinked to original sources

arXiv2026

A Census of the 200 Most Massive Galaxies Spectroscopically Observed with JWST at zspec $\sim$3-15

Massive galaxies provide strong tests of galaxy formation models, yet a comprehensive spectroscopic view of their properties and demographics in the early Universe has remained elusive. Here we present a JWST spectroscopic census of the 200 most massive galaxies at zspec~3-15, selected using an evolving stellar-mass threshold motivated by the halo mass function and anchored at log(Mstar)>10 at z~5. These galaxies represent the top 3% most massive systems among all publicly available prism observations. We derive their physical properties through joint SED fitting of spectroscopy and photometry, and construct a clean massive galaxy sample after removing LRDs and broad-line AGN contaminants. We find that the massive galaxy population evolves strongly with redshift: normal SFGs (Av<1 mag) dominate at z>~6, while dusty SFGs (Av>1 mag) and QGs become more common toward lower redshift. Dust attenuation decreases systematically toward higher redshift. We identify 29 massive QGs, including a population of recently quenched systems whose star formation declined rapidly within the past ~100 Myr. We further show that both the traditional UVJ and recently proposed (ugi)s selections suffer substantial inconsistency with the most massive galaxies at z>3, motivating a revised (ugi)s criterion calibrated using our spectroscopic sample. The inferred formation histories suggest at least two pathways toward quiescence: a dust-enriched pathway linking normal SFGs, dusty SFGs, and QGs, and a more direct pathway connecting normal SFGs and QGs. Massive normal SFGs appear to grow through both relatively gradual and rapid assembly modes. Together, these results suggest that rapid stellar-mass assembly, dust enrichment, and quenching were already shaping the evolutionary pathways of the most massive galaxies within the first billion years after the Big Bang.

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arXiv2026

Prospects for Observing Galaxy Spectral Energy Distribution from the Radio to the far-Infrared in the Era of Next-Generation Radio Telescopes

The superb sensitivity and angular resolution of the next-generation radio telescopes with combined frequency coverage of approximately over three orders of magnitude (100 MHz--100 GHz) will sample the radio and far-infrared (FIR) spectral energy distribution (SED) of galaxies and revolutionize the galaxy formation study at the epoch of re-ionization and beyond. We present a prospect of observing the radio--FIR continuum SEDs of galaxies in the redshift of up to $z\approx 20$ based on an ensemble of the simulated `energy balanced' panchromatic SED (from UV to FIR) extended to the radio. For `realistic' populations of UV star-forming galaxies and dusty star-forming galaxies, we simulate their SEDs by accounting for the CMB effect and the radio--IR correlation. The flux density evolution of the UV-bright star-forming galaxies and the dusty star-forming galaxies at the selected observing frequencies covered by the current (ALMA) and next generation (SKA and ngVLA) radio-millimeter telescopes, suggest that massive galaxies (M$_* \gtrsim 10^{10}$M$_{\odot}$) are detectable at any redshift ($0 90$GHz). In particular, when operating, the ngVLA high-frequency ($\approx 100$ GHz) band is capable of detecting galaxies with M$_* \gtrsim 10^{9}$M$_{\odot}$ almost independently from redshift and the SKA low-frequency observing window ($\lesssim1$ GHz) has sufficient sensitivity to detect M$_* \gtrsim 10^{10}$M$_{\odot}$ dusty star-forming galaxies up to the epoch of reionization ($z=5\sim7$). We also show that the brightness of anomalous microwave emission (AME) in the galaxy SED is insignificant if the galaxies are beyond the local Universe (e.g., $z\gtrsim 0.1$).

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arXiv2026

Multi-wavelength morphology and dust emission in low-redshift dwarf galaxies in COSMOS-Web with HST and JWST

Low-mass or dwarf galaxies (M$_{\ast}<10^{9}$ M${\odot}$) are abundant in the Universe, yet their formation and evolution remain poorly understood. Their enhanced sensitivity to feedback from star formation and active galactic nuclei (AGN) make them excellent laboratories to test whether feedback prescriptions in cosmological simulations accurately reproduce their interstellar medium (ISM) properties. We present JWST/NIRCam and MIRI imaging of nine dwarf galaxies from COSMOS-Web survey at redshift $z<0.08$, with star formation rates ranging from 0.003-0.3 M${\odot}$ yr$^{-1}$ and stellar masses of log M$_{\ast}\sim8-9$ M$_{\odot}$. The detection rate with both NIRCam and MIRI is 100\%, indicating that these dwarfs possess substantial ISM content. The detected sample includes a roughly equal mix of early-type and late-type dwarfs, suggesting that it is representative of the broader dwarf galaxy population in low-density environments. We find that the observed MIRI flux distributions are comparable to forward-modelled flux distributions of mass-matched simulated galaxies in TNG50. We further conduct a multi-wavelength morphological analysis complementing the JWST NIRCam and MIRI imaging with archival HST/ACS data, employing the CAS (concentration, asymmetry, smoothness) framework. Among the multi-wavelength images, MIRI exhibits the largest variation in CAS parameters, likely due to dust lanes and clumps in several galaxies, also suggested by Spectral Energy Distribution (SED) fitting. This suggests that the dust content in these systems may be higher than those implied by rest-frame optical or near-infrared observations alone. Upcoming UV/optical and mid-infrared spectroscopic follow-up will be critical for constraining the gas kinematics and dust grain properties of dwarf galaxies in low-density environments such as COSMOS.

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arXiv2025

Molecular Gas in Major Mergers Hosting Dual and Single AGN at <10 kpc Nuclear Separations

We present high-resolution ($\sim$50$-$100 pc) Atacama Large Millimeter Array (ALMA) observations of $^{12}$CO(2-1) or $^{12}$CO(1-0) emission in seven local ($z$ $\lesssim$ 0.05) major mergers -- five of which are dual active galactic nuclei (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 non-rotating components of the molecular gas -- the most likely contributor to future SMBH growth. We find that more massive SMBHs have higher surface densities of non-rotating 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 non-rotating 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.

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arXiv2025

The Stellar Morphology & Size of X-ray-selected Active Galactic Nuclei Host Galaxies Revealed by JWST

We investigate the stellar shape and size-mass relationship of X-ray selected Active Galactic Nuclei (AGN) host galaxies using the high-angular resolution and deep sensitivity in the near-infrared of the COSMOS-Web JWST survey field. We present the rest-frame 1-$\mu m$ size, stellar mass, Sersic index, axis-ratio, Gini-$M_{20}$ parameters of 690 moderate luminosity AGNs between redshift 0-3 and with stellar mass $\log M_s\sim 10.75$. We find that AGN host galaxies have an effective radius of 1-5 kpc, which is between star-forming (SFG) and quiescent galaxies (QGs) of the same stellar mass. AGN hosts have similar size-mass trends as SFG and QGs, being smaller at higher redshift for the same stellar mass. The slope of the size-mass relationship of AGN host galaxies is steeper than that of star-forming galaxies. Their rest-frame 1$\mu m$ stellar morphology indicates a significant spheroidal component. We observed a low merger fraction (6%) in our sample as well as substructures similar to disks, bars, and spiral arms in the residual images, which are in tension with evolutionary pathways that require major mergers. However, it may also be due to the different timescales between mergers and AGN activity.

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arXiv2025

JWST COSMOS-3D: Spectroscopic Census and Luminosity Function of [O III] Emitters at 6.75<z<9.05 in COSMOS

We present a catalogue of spectroscopically selected [OIII]+Hb emitters at 6.75<z<9.05 and the resulting [OIII] 5008 \AA Luminosity Function (LF) in the COSMOS field. We leverage the 0.33 deg$^2$ covered by COSMOS-3D using NIRCam/WFSS F444W to perform the largest spectroscopic search for [OIII] emitters at 6.75<z<9.05. We present our catalogue of 249 [OIII] emitters and their associated completeness function. The inferred constraints on the [OIII] LF enable us to characterise the knee of the [OIII] LF, resulting in improved [OIII] LF constraints at z~7,8. Notably, we find evidence for a decline of the [OIII] luminosity density between z~7 and z~8, which could be expected if the metallicity of [OIII] emitters, as well as the cosmic star-formation rate density, is declining at these redshifts. We find that theoretical models that reproduce the z~7,8 [OIII] LF do not reproduce well the [OIII] equivalent width distribution, pointing to potential challenges in the modelling of[OIII] and other nebular lines in the early Universe. Finally, we provide the first constraints on the cosmic variance of [OIII] emitters, estimating at 15% the fractional uncertainty for the z~7,8 [OIII] LF in the 0.33 deg$^2$ field. This estimate is in good agreement with that inferred from clustering, and shows that the [OIII] LF derived from smaller extragalactic legacy fields is strongly affected by cosmic variance. Our results highlight the fundamental role that wide-area JWST slitless surveys play to map the galaxy large-scale structure down into the reionisation era, serving as a springboard for a variety of science cases.

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arXiv2025

Parallel Application of Slitless Spectroscopy to Analyze Galaxy Evolution (PASSAGE): Survey Overview

During the second half of Cycle 1 of the James Webb Space Telescope (JWST), we conducted the Parallel Application of Slitless Spectroscopy to Analyze Galaxy Evolution (PASSAGE) program. PASSAGE received the largest allocation of JWST observing time in Cycle 1, 591 hours of NIRISS observations to obtain direct near-IR imaging and slitless spectroscopy. About two thirds of these were ultimately executed, to observe 63 high-latitude fields in Pure Parallel mode. These have provided more than ten thousand near-infrared grism spectrograms of faint galaxies. PASSAGE brings unique advantages in studying galaxy evolution: A) Unbiased spectroscopic search, without prior photometric pre-selection. By including the most numerous galaxies, with low masses and strong emission lines, slitless spectroscopy is the indispensable complement to any pre-targeted spectroscopy; B) The combination of several dozen independent fields to overcome cosmic variance; C) Near-infrared spectral coverage, often spanning the full range from 1.0--2.3 $\mu$m, with minimal wavelength gaps, to measure multiple diagnostic rest-frame optical lines, minimizing sensitivity to dust reddening; D) JWST's unprecedented spatial resolution, in some cases using two orthogonal grism orientations, to overcome contamination due to blending of overlapping spectra; E) Discovery of rare bright objects especially for detailed JWST followup. PASSAGE data are public immediately, and our team plans to deliver fully-processed high-level data products. In this PASSAGE overview, we describe the survey and data quality, and present examples of these accomplishments in several areas of current interest in the evolution of emission-line galaxy properties, particularly at low masses.

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arXiv2025

LATIS: A Sample of IGM-selected Protoclusters and Protogroups at $z \sim 2.5$

The Ly$\alpha$ Tomography IMACS Survey (LATIS) has produced large 3D maps of the intergalactic medium (IGM), providing a new window on the cosmic web at $z\sim2.5$. A key advantage of Ly$\alpha$ tomography is that it enables the discovery of overdense regions without the need to detect their galaxy members in spectroscopic surveys, circumventing possible selection biases. We use these maps to identify 37 IGM-selected overdensities as regions of strong and spatially coherent Ly$\alpha$ absorption. Simulations indicate that 85% of these are protoclusters, defined as the progenitors of $z=0$ halos with mass $M_{\rm desc} > 10^{14} M_{\odot}$, and that nearly all of the rest are protogroups ($10^{13.5} < M_{\rm desc} / M_{\odot} < 10^{14}$). We estimate the masses and space densities of the IGM-selected overdensities and show they are in accordance with mock surveys. We investigate the LATIS counterparts of some previously reported protoclusters, including the proto-supercluster Hyperion. We identify a new component of Hyperion beyond its previously known extent. We show that the Ly$\alpha$ transmission of the galaxy density peaks within Hyperion is consistent with a simple physical model (the fluctuating Gunn-Peterson approximation), suggesting that active galactic nucleus feedback or other processes have not affected the large-scale gas ionization within this structure as whole. The LATIS catalog represents an order-of-magnitude increase in the number of IGM-selected protogroups and protoclusters and will enable new investigations of the connections between galaxies and their large-scale environments at cosmic noon.

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arXiv2025

LATIS: Comparing Galaxy and IGM Tomography Maps as Tracers of Large-scale Structure and Protoclusters at $z \sim 2.5$

We investigate the consistency of intergalactic medium (IGM) tomography and galaxy surveys as tracers of the cosmic web and protoclusters at $z \sim 2.5$. We use maps from the Ly$\alpha$ Tomography IMACS Survey (LATIS), which trace the distributions of Lyman-break galaxies (LBGs) and IGM Ly$\alpha$ absorption on $\simeq 4$ $h^{-1}$ cMpc scales within the same large volume. Overall, the joint distribution of IGM absorption and LBG density is well constrained and accurately described by a simple physical model. However, we identify several exceptional locations exhibiting strong IGM absorption indicative of a massive protocluster, yet no coincident overdensity of LBGs. As discussed by Newman et al., whose results we revise using the complete LATIS survey data, these are candidate ultraviolet (UV)-dim protoclusters that may harbor distinct galaxy populations missed by rest-UV spectroscopic surveys. We present follow-up observations targeting one such candidate embedded within Antu, an extended region of IGM absorption at $z=2.685$ that contains five IGM-selected protoclusters and has a total mass of $3 \times 10^{15}~M_{\odot}$. Ly$\alpha$ emitters trace the overall structure of Antu but avoid the center of the candidate UV-dim protocluster, which also appears to contain no submillimeter-selected sources. A near-infrared spectroscopic galaxy census is needed to determine whether this large region is dominated by galaxies with reduced or absent star-formation activity. This work adds to a growing and puzzling literature on discrepancies among different galaxy and IGM tracers, whose resolution promises to shed light on the early stages of environment-dependent galaxy evolution.

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arXiv2025

Clumpiness of galaxies revealed in the near-infrared with COSMOS-Web

Clumps in the rest-frame UV emission of galaxies have been observed for decades. Since the launch of the James Webb Space Telescope (JWST), a large population is detected in the rest-frame near-infrared (NIR), raising questions about their formation mechanism. We investigate the presence and properties of NIR over-densities (hereafter substructures) in star-forming and quiescent galaxies at 1 < z < 4 to understand their link to the evolution of their host galaxy. We identify substructures in JWST/NIRCam F277W and F444W residual images at a rest-frame wavelength of 1 um. The fraction of galaxies with substructures with M* > 10^9 Msun has been steadily decreasing with cosmic time from 40% at z = 4 to 10% at z = 1. Clumps, the main small substructures in the rest-frame NIR, are the most common type and are much fainter (2% of the flux) than similar UV clumps in the literature. Nearly all galaxies at the high-mass end of the main sequence (MS), starburst, and green valley regions have substructures. However, we do not find substructures in low-mass galaxies in the green valley and red sequence. Although massive galaxies on the MS and in the green valley have a 40% probability of hosting multiple clumps, the majority of clumpy galaxies host only a single clump. The fraction of clumpy galaxies in the rest-frame NIR is determined by the stellar mass and SFR of the host galaxies. Its evolution with redshift is due to galaxies moving towards lower SFRs at z < 2 and the build-up of low-mass galaxies in the green valley and red sequence. Based on their spatial distribution in edge-on galaxies, we infer that most of substructures are produced in-situ via disk fragmentation. Galaxy mergers may still play an important role at high stellar masses, especially at low SFR.

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arXiv2025

COSMOS-Web: Estimating Physical Parameters of Galaxies Using Self-Organizing Maps

The COSMOS-Web survey, with its unparalleled combination of multiband data, notably, near-infrared imaging from JWST's NIRCam (F115W, F150W, F277W, and F444W), provides a transformative dataset down to $\sim28$ mag (F444W) for studying galaxy evolution. In this work, we employ Self-Organizing Maps (SOMs), an unsupervised machine learning method, to estimate key physical parameters of galaxies -- redshift, stellar mass, star formation rate (SFR), specific SFR (sSFR), and age -- directly from photometric data out to $z=3.5$. SOMs efficiently project high-dimensional galaxy color information onto 2D maps, showing how physical properties vary among galaxies with similar spectral energy distributions. We first validate our approach using mock galaxy catalogs from the HORIZON-AGN simulation, where the SOM accurately recovers the true parameters, demonstrating its robustness. Applying the method to COSMOS-Web observations, we find that the SOM delivers robust estimates despite the increased complexity of real galaxy populations. Performance metrics ($\sigma_{\mathrm{NMAD}}$ typically between $0.1$--$0.3$, and Pearson correlation between $0.7$ and $0.9$) confirm the precision of the method, with $\sim$ $70\%$ of predictions within 1$\sigma$ dex of reference values. Although redshift estimation in COSMOS-Web remains challenging (median $\sigma_{\mathrm{NMAD}} = 0.04$), the overall success of the highlights its potential as a powerful and interpretable tool for galaxy parameter estimation. A key advance of this work is the use of JWST/NIRCam photometry, particularly the F444W band, which enhances SOM training and allows more accurate estimation of stellar mass, SFR, and age compared to previous studies using IRAC/Spitzer filters.

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arXiv2025

COSMOS Web: Morphological quenching and size-mass evolution of brightest group galaxies from z = 3.7

We present a comprehensive study of the structural evolution of Brightest Group Galaxies (BGGs) from redshift $z \simeq 0.08$ to $z = 3.7$ using the \textit{James Webb Space Telescope}'s 255h COSMOS-Web program. This survey provides deep NIRCam imaging in four filters (F115W, F150W, F277W, F444W) across $\sim 0.54~\mathrm{deg}^2$ and MIRI coverage in $\sim 0.2~\mathrm{deg}^2$ of the COSMOS field. High-resolution NIRCam imaging enables robust size and morphological measurements, while multiwavelength photometry yields stellar masses, SFRs, and S\'ersic parameters. We classify BGGs as star-forming and quiescent using both rest-frame NUV--$r$--$J$ colors and a redshift-dependent specific star formation rate (sSFR) threshold. Our analysis reveals: (1) quiescent BGGs are systematically more compact than their star-forming counterparts and exhibit steeper size--mass slopes; (2) effective radii evolve as $R_e \propto (1+z)^{-\alpha}$, with $\alpha = 1.11 \pm 0.07$ (star-forming) and $1.40 \pm 0.09$ (quiescent); (3) star formation surface density ($\Sigma_{\mathrm{SFR}}$) increases with redshift and shows stronger evolution for massive BGGs ($\log_{10}(M_\ast/M_\odot) \geq 10.75$); (4) in the $\Sigma_*$--sSFR plane, a structural transition marks the quenching process, with bulge-dominated systems comprising over 80\% of the quiescent population. These results highlight the co-evolution of structure and star formation in BGGs, shaped by both internal and environmental processes, and establish BGGs as critical laboratories for studying the baryonic assembly and morphological transformation of central galaxies in group-scale halos.

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arXiv2025

On Soft Clustering For Correlation Estimators

Properly estimating correlations between objects at different spatial scales necessitates $\mathcal{O}(n^2)$ distance calculations. For this reason, most widely adopted packages for estimating correlations use clustering algorithms to approximate local trends. However, methods for quantifying the error introduced by this clustering have been understudied. In response, we present an algorithm for estimating correlations that is probabilistic in the way that it clusters objects, enabling us to quantify the uncertainty caused by clustering simply through model inference. These soft clustering assignments enable correlation estimators that are theoretically differentiable with respect to their input catalogs. Thus, we also build a theoretical framework for differentiable correlation functions and describe their utility in comparison to existing surrogate models. Notably, we find that repeated normalization and distance function calls slow gradient calculations and that sparse Jacobians destabilize precision, pointing towards either approximate or surrogate methods as a necessary solution to exact gradients from correlation functions. To that end, we close with a discussion of surrogate models as proxies for correlation functions. We provide an example that demonstrates the efficacy of surrogate models to enable gradient-based optimization of astrophysical model parameters, successfully minimizing a correlation function output. Our numerical experiments cover science cases across cosmology, from point spread function (PSF) modeling efforts to gravitational simulations to galaxy intrinsic alignment (IA).

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arXiv2024

PANORAMIC: Discovery of an Ultra-Massive Grand-Design Spiral Galaxy at $z\sim5.2$

We report the discovery of an ultra-massive grand-design red spiral galaxy, named Zh\'ul\'ong (Torch Dragon), at $z_{\rm phot} = 5.2^{+0.3}_{-0.2}$ in the JWST PANORAMIC survey, identified as the most distant bulge+disk galaxy candidate with spiral arms known to date. Zh\'ul\'ong displays an extraordinary combination of properties: 1) a classical bulge centered in a large, face-on exponential stellar disk (half-light radius of $R_{\rm e} = 3.7 \pm 0.1 \, \mathrm{kpc}$), with spiral arms extending across 19 kpc; 2) a clear transition from the red, quiescent core ($F150W-F444W=3.1$ mag) with high stellar mass surface density ($\log(\Sigma M_{\star}/M_{\odot} \, \mathrm{kpc}^{-2}) = 9.91_{-0.09}^{+0.11}$) to the star-forming outer regions, as revealed by spatially resolved SED analysis, which indicates significant inside-out galaxy growth; 3) an extremely high stellar mass at its redshift, with $\log (M_{\star}/M_{\odot})=11.03_{-0.08}^{+0.10}$ comparable to the Milky Way, and an implied baryon-to-star conversion efficiency ($\epsilon \sim 0.3$) that is 1.5 times higher than even the most efficient galaxies at later epochs; 4) despite an active disk, a relatively modest overall star formation rate ($\mathrm{SFR} =66_{-46}^{+89} ~M_{\odot} \, \mathrm{yr}^{-1}$), which is $>$0.5 dex below the star formation main sequence at $z \sim 5.2$ and $>$10 times lower than ultra-massive dusty galaxies at $z=5-6$. Altogether, Zh\'ul\'ong shows that mature galaxies emerged much earlier than expected in the first billion years after the Big Bang through rapid galaxy formation and morphological evolution. Our finding offers key constraints for models of massive galaxy formation and the origin of spiral structures in the early universe.

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arXiv2024

EELG1002: A Record-Breaking [OIII]+H$\beta$ EW $\sim 3700$\AA~Galaxy at $z \sim 0.8$ -- Analog of Early Galaxies?

We present a detailed analysis of EELG1002: a $z = 0.8275$ EELG identified within archival Gemini/GMOS spectroscopy as part of the on-going COSMOS Spectroscopic Archive. We find EELG1002 is a low-mass ($\sim10^{8}$ M$_\odot$), compact ($\sim530$ pc), bursty star-forming galaxy with a $\sim15-35$ Myr mass doubling timescale. EELG1002 has record-breaking rest-frame [O{\sc iii}]+H$\beta$~EW $\sim3100-3700$\AA; $\sim32-36\times$ higher than typical $z \sim 0.8$ [O{\sc iii}]~emitters with similar stellar mass and higher than typical $z > 5$ galaxies. We find no clear evidence of an AGN suggesting the emission lines are star formation driven. EELG1002 is chemically unevolved (direct $T_e$; $12+\log_{10}(\textrm{O/H})\sim7.52$ consistent with $z>5$ galaxies at fixed stellar mass) and may be undergoing a first intense, bursty star formation phase analogous to conditions expected of galaxies in the early Universe. We find evidence for a highly energetic ISM ([O{\sc iii}]/[O{\sc ii}]~$\sim9$) and hard ionizing radiation field (elevated [Ne{\sc iii}]/[O{\sc ii}]~at fixed [O{\sc iii}]/[O{\sc ii}]). Coupled with its compact, metal-poor, and actively star-forming nature, EELG1002 is found to efficiently produce ionizing photons ($\xi_\mathrm{ion}\sim10^{25.74}~$erg$^{-1}$ Hz) and may have $\sim10-20\%~$LyC escape suggesting such sources may be important analogs of galaxies responsible for reionization. We find dynamical mass of $\sim10^9~$M$_\odot$~suggesting copious amounts of gas to support intense star formation as also suggested by identified Illustris-TNG analogs. EELG1002 may be an ideal low-$z$ laboratory of galaxies in the early Universe and demonstrates how archival datasets can support high-$z$ science and next-generation surveys planned with \textit{Euclid} and \textit{Roman}.

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arXiv2024

A photo-z cautionary tale: Redshift confirmation of COSBO-7 at z=2.625

Photometric redshifts are widely used in studies of dusty star-forming galaxies (DSFGs), but catastrophic photo-$z$ failure can undermine all redshift-dependent results. Here we report the spectroscopic redshift confirmation of COSBO-7, a strongly lensed DSFG in the COSMOS-PRIMER field. Recently, a photometric redshift solution of $z\gtrsim7.0$ was reported for COSBO-7 based on ten bands of {\it James Webb} Space Telescope (JWST) NIRCam and MIRI imaging data. This $z$ value was favored by four independent spectral energy distribution (SED) fitting codes, and the result provided an appealing candidate for the most distant massive DSFG known to date. This photo-$z$ solution was also supported by a single line detection in Atacama Large Millimeter Array (ALMA) Band 3 consistent with CO(7-6) at $z=7.46$. However, our new ALMA observations robustly detect two lines in Band 6 identified as CO(7-6) and [CI](2-1) at $z_{\rm spec}=2.625$, and thus the Band 3 line as CO(3-2). These three robust line detections decidedly place COSBO-7 at $z=2.625$, refuting the photo-$z$ solution. We derive physical parameters by fitting near-infrared(NIR)-to-millimeter(mm) photometry and lens modeling, revealing that COSBO-7 is a main sequence galaxy. We examine possible reasons for this photo-$z$ failure and attribute it to (1) the likely underestimation of photometric uncertainties at 0.9\,$\mu$m and 1.15 \,$\mu$m; and (2) the lack of photometry at wavelengths beyond 20\,$\mu$m. Notably, we recover a bona fide $z_{\rm phot}\sim 2.3$ by including the existing MIPS $24\,\mu$m photometry, demonstrating the critical importance of mid-infrared (MIR) data in bolstering photo-$z$ measurements. This work highlights a common challenge in modeling the SEDs of DSFGs, and provides a cautionary tale regarding the reliability of photometric redshifts as well as pseudo-spectroscopic redshifts based on single line detection.

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arXiv2024

The $M_{\rm BH}-M_*$ relation up to $z\sim2$ through decomposition of COSMOS-Web NIRCam images

Our knowledge of relations between supermassive black holes and their host galaxies at $z\gtrsim1$ is still limited, even though being actively sought out to $z\sim6$. Here, we use the high resolution and sensitivity of JWST to measure the host galaxy properties for 107 X-ray-selected type-I AGNs at $0.68<z<2.5$ with rest-frame optical/near-infrared imaging from COSMOS-Web and PRIMER. Black hole masses ($\log\left(M_{\rm BH}/M_\odot\right)\sim6.9-9.6$) are available from previous spectroscopic campaigns. We extract the host galaxy components from four NIRCam broadband images and the HST/ACS F814W image by applying a 2D image decomposition technique. We detect the host galaxy for $\sim90\%$ of the sample after subtracting the unresolved AGN emission. With host photometry free of AGN emission, we determine the stellar mass of the host galaxies to be $\log\left(M_*/M_\odot\right)\sim9.5-11.6$ through SED fitting and measure the evolution of the mass relation between SMBHs and their host galaxies. Considering selection biases and measurement uncertainties, we find that the $M_\mathrm{ BH}/M_*$ ratio evolves as $\left(1+z\right)^{0.48_{-0.62}^{+0.31}}$ thus remains essentially constant or exhibits mild evolution up to $z\sim2.5$. We also see an amount of scatter ($\sigma_{\mu}=0.30^{+0.14}_{-0.13}$), similar to the local relation and consistent with low-$z$ studies, and a non-causal cosmic assembly history where mergers contribute to the statistical averaging towards the local relation is still feasible. We highlight improvements to come with larger samples from JWST and, particularly, Euclid, which will exceed the statistical power of current wide and deep surveys.

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arXiv2023

Resolving galactic-scale obscuration of X-ray AGN at $z\gtrsim1$ with COSMOS-Web

A large fraction of the accreting supermassive black hole population is shrouded by copious amounts of gas and dust, particularly in the distant ($z\gtrsim1$) Universe. While much of the obscuration is attributed to a parsec-scale torus, there is a known contribution from the larger-scale host galaxy. Using JWST/NIRCam imaging from the COSMOS-Web survey, we probe the galaxy-wide dust distribution in X-ray selected AGN up to $z\sim2$. Here, we focus on a sample of three AGNs with their host galaxies exhibiting prominent dust lanes, potentially due to their edge-on alignment. These represent 27% (3 out of 11 with early NIRCam data) of the heavily obscured ($N_H>10^{23}$ cm$^{-2}$) AGN population. With limited signs of a central AGN in the optical and near-infrared, the NIRCam images are used to produce reddening maps $E(B-V)$ of the host galaxies. We compare the mean central value of $E(B-V)$ to the X-ray obscuring column density along the line-of-sight to the AGN ($N_H\sim10^{23-23.5}$ cm$^{-2}$). We find that the extinction due to the host galaxy is present ($0.6\lesssim E(B-V) \lesssim 0.9$; $1.9 \lesssim A_V \lesssim 2.8$) and significantly contributes to the X-ray obscuration at a level of $N_H\sim10^{22.5}$ cm$^{-2}$ assuming an SMC gas-to-dust ratio which amounts to $\lesssim$30% of the total obscuring column density. These early results, including three additional cases from CEERS, demonstrate the ability to resolve such dust structures with JWST and separate the different circumnuclear and galaxy-scale obscuring structures.

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