arXiv subjects

Louise Paquereau

Publications and source records attributed to Louise Paquereau.

At least 37 records · Page 2Linked to original sources

arXiv2025

Physical properties of galaxies and the UV Luminosity Function from $z\sim6$ to $z\sim14$ in COSMOS-Web

We present measurements of the rest-frame ultraviolet luminosity function (UVLF) in three redshift bins over $z\sim5.5$-14 from the JWST COSMOS-Web survey. Our samples, selected using the dropout technique in the HST/ACS F814W, JWST/NIRCam F115W, and F150W filters, contain a total of 3099 galaxies spanning a wide luminosity range from faint ($M_{\rm UV}\sim-19$ mag) to bright ($M_{\rm UV}\sim-22.5$ mag). The galaxies are undergoing rapid star formation, with blue stellar populations. Surprisingly, their median UV spectral slope $β$ does not evolve at $z>8$, suggesting minimal dust, or physical separation of dust and star formation at early epochs. The measured UVLF exhibits an excess at the bright-end ($M_{\rm UV}<-21$ mag) compared to pre-JWST empirical results and theoretical predictions of an evolving Schechter function, with the excess beginning at $z\sim9$ and becoming increasingly prominent toward $z\sim12$. Our analysis suggests that reproducing the observed abundance of UV-bright galaxies at high redshift requires a combination of physical processes, including elevated star formation efficiencies, moderate levels of stochasticity in galaxy luminosities, and minimal dust attenuation.

astro-ph.GA↗

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 Sérsic 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 $R_e \propto (1+z)^{-α}$, with $α= 1.11 \pm 0.07$ (star-forming) and $1.40 \pm 0.09$ (quiescent); (3) star formation surface density ($Σ_{\mathrm{SFR}}$) increases with redshift and shows stronger evolution for massive BGGs ($\log_{10}(M_\ast/M_\odot) \geq 10.75$); (4) in the $Σ_*$--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

The COSMOS-Web deep galaxy group catalog up to $z=3.7$

Galaxy groups with $M_{tot} \lesssim 10^{14}$ $M_\odot$ and up to a few tens of members are the most common galaxy environment, marking the transition between field and massive clusters. Identifying groups plays a crucial role in understanding structure formation and galaxy evolution. Modern deep surveys allow us to build well-characterized samples of groups up to the regime where structures were taking shape. We aimed to build the largest deep catalog of galaxy groups to date over the COSMOS-Web field effective area of 0.45 deg$^2$, leveraging the deep high quality data of the new COSMOS-Web photometric catalog resulted from the James Webb Space Telescope observations of the COSMOS-Web field. We performed the group search with the AMICO algorithm, a linear matched filter based on an analytical model for the group signal. AMICO has already been tested in wide and deep field surveys, including COSMOS data up to $z=2$. In this work, we tested the algorithm performances at even higher redshift and searched for protocluster cores at $z>2$. We compiled a list of known protoclusters in COSMOS at $2 \leq z \leq 3.7$, matched them with our detections and studied the clustering of the detected cores. We estimated purity and completeness of our sample by creating data-driven mocks with the SinFoniA code and linked signal-to-noise to purity. We detected 1678 groups in the COSMOS-Web field up to $z=3.7$, including lists of members extending nearly two magnitudes deeper than the previous AMICO-COSMOS catalog. 756 groups were detected with purity of 80\%. More than 500 groups have their redshift confirmed by assigning spectroscopic counterparts. This group catalog offers a unique opportunity to explore galaxy evolution in different environments spanning $\sim$12 Gyr and to study groups, from the least rich population to the formation of the most massive clusters.

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arXiv2025

COSMOS-Web: Comprehensive Data Reduction for Wide-Area JWST NIRCam Imaging

We present the data reduction methodology used for the COSMOS-Web survey JWST NIRCam data. Covering 0.54 deg^2 with four broadband filters (F115W, F150W, F277W, F444W) and a total exposure time of approximately 270 hours, COSMOS-Web represents the largest contiguous field surveyed during JWST Cycle 1, posing unique data reduction challenges due to its extensive scale. By combining the official JWST Calibration Pipeline with custom improvements for noise removal, background subtraction, and astrometric alignment, we achieve high fidelity science-ready mosaics. We detail the systematic approach employed in the three stages of the JWST Calibration Pipeline. The data, collected in three epochs from January 2023 to January 2024, encompass 152 visits and have been processed into 20 mosaic tiles to optimize computational efficiency and data processing. The final data products achieve 5 sigma depths of 26.7-28.3 AB mag in 0.15" apertures. The processed and calibrated datasets are made available to the public.

astro-ph.IM↗

arXiv2025

COSMOS-Web: MIRI Data Reduction and Number Counts at 7.7$μ$m using JWST

The COSMOS-Web survey is the largest JWST Cycle 1 General Observer program covering a contiguous ~0.54 deg$^2$ area with NIRCam imaging in four broad-band filters and a non-contiguous ~0.2 deg$^2$ with parallel MIRI imaging in a single broad-band filter, F770W. Here we present a comprehensive overview of the MIRI imaging observations, the data reduction procedure, the COSMOS-Web MIRI photometric catalog, and the first data release including the entire COSMOS-Web MIRI coverage. Data reduction is predominantly based on the JWST Science Calibration Pipeline with an additional step involving custom background subtraction to mitigate the presence of strong instrumental features and sky background in the MIRI images. We reach 5$σ$ (point source) limiting depths ($m_{F770W}$~25.51 based on $r$~0.3'' circular apertures) that are significantly better than initial expectations. We create a COSMOS-Web MIRI catalog based on the images presented in this release and compare the F770W flux densities with the Spitzer/IRAC CH4 measurements from the COSMOS2020 catalog for CH4 detections with S/N $>5$. We find that these are in reasonable agreement with a small median offset of $<0.05$ mag. We also derive robust 7.7$μ$m number counts spanning five orders of magnitude in flux ($\sim$0.2-2300 $μ$Jy) $\unicode{x2013}$ making COSMOS-Web the only JWST survey to date to efficiently sample such a large flux range $\unicode{x2013}$ which is in good agreement with estimates from other JWST and IRAC surveys.

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arXiv2025

COSMOS2025: The COSMOS-Web galaxy catalog of photometry, morphology, redshifts, and physical parameters from JWST, HST, and ground-based imaging

We present COSMOS2025, the COSMOS-Web catalog of photometry, morphology, photometric redshifts and physical parameters for more than 700,000 galaxies in the Cosmic Evolution Survey (COSMOS) field. This catalog is based on our \textit{James Webb Space Telescope} 255\,h COSMOS-Web program, which provides deep near-infrared imaging in four NIRCam (F115W, F150W, F277W, F444W) and one MIRI (F770W) filter over the central $\sim 0.54 {\, \rm deg}^2$ ($\sim 0.2 {\, \rm deg}^2$ for MIRI) in COSMOS. These data are combined with ground- and space-based data to derive photometric measurements of NIRCam-detected sources using both fixed-aperture photometry (on the space-based bands) and a profile-fitting technique on all 37 bands spanning 0.3-8 micron. We provide morphology for all sources from complementary techniques including profile fitting and machine-learning classification. We derive photometric redshifts, physical parameters and non-parametric star formation histories from spectral energy distribution (SED) fitting. The catalog has been extensively validated against previous COSMOS catalogs and other surveys. Photometric redshift accuracy measured using spectroscopically confirmed galaxies out to $z\sim9$ reaches $σ_{\rm MAD} = 0.012$ at $m_{\rm F444W}<28$ and remains at $σ_{\rm MAD} \lesssim 0.03$ as a function of magnitude, color, and galaxy type. This represents a factor of $\sim 2$ improvement at 26 AB mag compared to COSMOS2020. The catalog is approximately 80\% complete at $\log(M_{\star}/{\rm M}_{\odot}) \sim 9$ at $z \sim 10$ and at $\log(M_{\star}/{\rm M}_{\odot}) \sim 7$ at $z \sim 0.2$, representing a gain of 1\,dex compared to COSMOS2020. COSMOS2025 represents the definitive COSMOS-Web catalog. It is provided with complete documentation, together with redshift probability distributions, and it is ready for scientific exploitation today.

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arXiv2025

Tracing the galaxy-halo connection with galaxy clustering in COSMOS-Web from z = 0.1 to z ~ 12

We explore the evolving relationship between galaxies and their dark matter halos from $z \sim 0.1$ to $z \sim 12$ using mass-limited angular clustering measurements in the 0.54 deg$^2$ of the COSMOS-Web survey. This study provides the first measurements of the mass-limited two-point correlation function at $z \ge 10$ and a consistent analysis spanning 13.4 Gyr of cosmic history, setting new benchmarks for future simulations and models. Using a halo occupation distribution (HOD) framework, we derive characteristic halo masses and the stellar-to-halo mass relationship (SHMR) across redshifts and stellar mass bins. Our results first indicate that HOD models fit data at $z \ge 2.5$ best when incorporating a non-linear scale-dependent halo bias, boosting clustering at non-linear scales (r = 10-100 kpc). We find that galaxies at z > 10.5 with $\log(M_\star / M_\odot) \ge 8.85$ are hosted by halos with $M_{\rm h} \sim 10^{10.5}\,M_\odot$, achieving a star formation efficiency (SFE) $M_\star / (f_b M_{\rm h}) $ up to 1 dex higher than at $z \le 1$. The high galaxy bias at $z \ge 8$ suggests that these galaxies reside in massive halos with intrinsic high SFE. Our SHMR evolves significantly with redshift, starting high at $z \ge 10.5$, decreasing until $z \sim 2 - 3$, then increasing again until the present. Current simulations fail to reproduce both massive high-$z$ galaxies and this evolution, while semi-empirical models linking SFE to halo mass, accretion rates, and redshift align with our findings. We propose that $z > 8$ galaxies experience bursty star formation without significant feedback altering their growth, driving the rapid growth of massive galaxies observed by JWST. Over time, increasing feedback efficiency and exponential halo growth suppress star formation. At $z \sim 2 - 3$ and after, halo growth slows down while star formation continues, supported by gas reservoirs in halos.

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arXiv2025

COSMOS-Web: Unraveling the Evolution of Galaxy Size and Related Properties at $2<z<10$

We measure galaxy sizes from $2 < z < 10$ using COSMOS-Web, the largest-area JWST imaging survey to date, covering $\sim$0.54 deg$^2$. We analyze the rest-frame optical (~5000A) size evolution and its scaling relation with stellar mass ($R_e\propto M_*^α$) for star-forming and quiescent galaxies. For star-forming galaxies, the slope $α$ remains approximately 0.20 at $2 < z < 8$, showing no significant evolution over this redshift range. At higher redshifts, the slopes are $-0.13 \pm 0.15$ and $0.37 \pm 0.36$ for $8 < z < 9$ and $9 < z < 10$, respectively. At fixed galaxy mass, the size evolution for star-forming galaxies follows $R_e \propto (1+z)^{-β}$, with $β= 1.21 \pm 0.05$. For quiescent galaxies, the slope is steeper $α\sim 0.5$-$0.8$ at $2 < z < 5$, and $β=0.81\pm0.26$. We find that the size-mass relation is consistent between UV and optical at $z < 8$ for star-forming galaxies. However, we observe a decrease in the slope from UV to optical at $z > 8$, with a tentative negative slope in the optical at $8 < z < 9$, suggesting a complex interplay between intrinsic galaxy properties and observational effects such as dust attenuation. We discuss the ratio between galaxies' half-light radius, and underlying halos' virial radius, $R_{vir}$, and find the median value of $R_e/R_{vir}=2.7\%$. The star formation rate surface density evolves as $\logΣ_\text{SFR} = (0.20\pm0.08)\,z+(-0.65\pm0.51)$, and the $Σ_\text{SFR}$-$M_*$ relation remains flat at $2 3$ provides new insights into galaxy size and related properties in the rest-frame optical.

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arXiv2025

Constraints on the early Universe star formation efficiency from galaxy clustering and halo modeling of H$α$ and [O III] emitters

We develop a theoretical framework to provide observational constraints on the early Universe galaxy-halo connection by combining measurements of the UV luminosity function (UVLF) and galaxy clustering via the 2-point correlation function (2PCF). We implemented this framework in the FRESCO and CONGRESS JWST NIRCam/grism surveys by measuring the 2PCF of spectroscopically selected samples of H$α$ and [OIII] emitters at $3.8 9$ shows that a constant SFE-$M_{\rm h}$ fixed at $z=8$ cannot reproduce the observed UVLF and neither high maximum SFE nor high stochasticity alone can explain the high abundances of luminous galaxies seen by JWST. Extending the analysis of the UVLF and 2PCF to $z>9$ measured from wider surveys will be crucial in breaking degeneracies.

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arXiv2025

The COSMOS-Web Lens Survey (COWLS) II: depth, resolution, and NIR coverage from JWST reveal 17 spectacular lenses

The COSMOS-Web Lens Survey (COWLS) presents the first systematic search for strong gravitational lenses in the COSMOS-Web field using data from the \textit{James Webb} Space Telescope (\textit{JWST}). Using high-resolution NIRCam imaging, we visually inspected over 42\,660 galaxies and identified over 400 lensing candidates. From this sample and based on \textit{JWST}/NIRCam imaging only, we report here the 17 most obvious and spectacular strong lensing systems. These lenses, characterised by large Einstein rings and arcs and their distinct lens and source colours, were found through only the visual inspection of the lens-light-subtracted image data and were immediately visible due to their spectacular appearance. We showcase how spectacular strong lenses are at the extremes of lens parameter space. Their exceptionally high signal-to-noise, multi-wavelength imaging enables unprecedented lensing analysis, including `\textit{HST}-dark' source galaxies that are also invisible in the deeper bluer \textit{JWST} wavebands, enabling clean deblending between the lens and the source. Sources may exhibit dramatic morphological changes across wavelengths, and dust absorption within lenses may be detectable by eye. No other instrument, including the \textit{Hubble} Space Telescope, can discover or image such lenses with comparable detail. We estimate that \textit{JWST} uncovers a new spectacular lens approximately every 10 to 12 NIRCam pointings, suggesting that over 40 such lenses remain undetected within its first three years of observations. All COWLS data is publicly available on GitHub.

astro-ph.GA↗

arXiv2025

Going deeper into the dark with COSMOS-Web: JWST unveils the total contribution of Radio-Selected NIRfaint galaxies to the cosmic Star Formation Rate Density

We present the first follow-up with JWST of radio-selected NIRfaint galaxies as part of the COSMOS-Web survey. By selecting galaxies detected at radio frequencies ($S_{\rm 3 GHz}>11.5$ $μ$Jy; i.e. S/N$>5$) and with faint counterparts at NIR wavelengths (F150W$>26.1$ mag), we collect a sample of 127 likely dusty star-forming galaxies (DSFGs). We estimate their physical properties through SED fitting, compute the first radio luminosity function for these types of sources, and their contribution to the total cosmic star formation rate density. Our analysis confirms that these sources represent a population of highly dust-obscured ($\langle A_{\rm v} \rangle \sim3.5$ mag), massive ($\langle M_\star \rangle \sim10^{10.8}$ M$_\odot$) and star-forming galaxies ($\langle {\rm SFR} \rangle\sim300$ M$_\odot$ yr$^{-1}$) located at $\langle z \rangle\sim3.6$, representing the high-redshift tail of the full distribution of radio sources. Our results also indicate that these galaxies could dominate the bright end of the radio luminosity function and reach a total contribution to the cosmic star formation rate density equal to that estimated only considering NIR-bright sources at $z\sim4.5$. Finally, our analysis further confirms that the radio selection can be employed to collect statistically significant samples of DSFGs, representing a complementary alternative to the other selections based on JWST colors or detection at FIR/(sub)mm wavelengths.

astro-ph.GA↗

arXiv2024

Not-so-little Red Dots: Two massive and dusty starbursts at z~5-7 pushing the limits of star formation discovered by JWST in the COSMOS-Web survey

We present the properties of two candidate massive ($M_\star\sim10^{11}M_\odot$) and dusty ($A_{\rm v}>2.5$ mag) galaxies at $z=5-7$ in the first 0.28 deg$^2$ of the COSMOS-Web survey. One object is spectroscopically confirmed at $z_{\rm spec}=5.051$, while the other has a robust $z_{\rm phot}=6.7\pm0.3$. Thanks to their extremely red colors ($F277W-F444W\sim1.7$ mag), these galaxies satisfy the nominal color-selection for the widely-studied ``little red dot" (LRD) population with the exception of their spatially-resolved morphologies. The morphology of our targets allows us to conclude that their red continuum is dominated by highly obscured stellar emission and not by reddened nuclear activity. Using a variety of SED-fitting tools and star formation histories, we estimate the stellar masses to be $\log(M_\star)=11.32^{+0.07}_{-0.15}$ $M_\odot$ and $\log(M_\star)=11.2^{+0.1}_{-0.2}$ $M_\odot$, respectively, with a red continuum emission dominated by a recent episode of star formation. We then compare their number density to the halo mass function to infer stellar baryon fractions of $ε_\star\sim0.25$ and $ε_\star\sim0.5$. Both are significantly higher than what is commonly observed in lower-z galaxies or more dust-obscured galaxies at similar redshifts. With very bright ultra-high-z Lyman-Break Galaxies and some non-AGN dominated LRDs, such ``extended" LRDs represent another population that may require very efficient star formation at early times.

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arXiv2024

COSMOS-Web: The over-abundance and physical nature of "little red dots"--Implications for early galaxy and SMBH assembly

JWST has revealed a population of compact and extremely red galaxies at $z>4$, which likely host active galactic nuclei (AGN). We present a sample of 434 ``little red dots'' (LRDs), selected from the 0.54 deg$^2$ COSMOS-Web survey. We fit galaxy and AGN SED models to derive redshifts and physical properties; the sample spans $z\sim5$-$9$ after removing brown dwarf contaminants. We consider two extreme physical scenarios: either LRDs are all AGN, and their continuum emission is dominated by the accretion disk, or they are all compact star-forming galaxies, and their continuum is dominated by stars. If LRDs are AGN-dominated, our sample exhibits bolometric luminosities $\sim10^{45-47}$ erg\,s$^{-1}$, spanning the gap between JWST AGN in the literature and bright, rare quasars. We derive a bolometric luminosity function (LF) $\sim100$ times the (UV-selected) quasar LF, implying a non-evolving black hole accretion density of $\sim10^{-4}$ M$_\odot$ yr$^{-1}$ Mpc$^{-3}$ from $z\sim2$-$9$. By contrast, if LRDs are dominated by star formation, we derive stellar masses $\sim10^{8.5-10}\,M_\odot$. MIRI/F770W is key to deriving accurate stellar masses; without it, we derive a mass function inconsistent with $Λ$CDM. The median stellar mass profile is broadly consistent with the maximal stellar mass surface densities seen in the nearby universe, though the most massive $\sim50$\% of objects exceed this limit, requiring substantial AGN contribution to the continuum. Nevertheless, stacking all available X-ray, mid-IR, far-IR/sub-mm, and radio data yields non-detections. Whether dominated by dusty AGN, compact star-formation, or both, the high masses/luminosities and remarkable abundance of LRDs implies a dominant mode of early galaxy/SMBH growth.

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arXiv2023

Uncovering a Massive z~7.7 Galaxy Hosting a Heavily Obscured Radio-Loud QSO Candidate in COSMOS-Web

In this letter, we report the discovery of the highest redshift, heavily obscured, radio-loud AGN candidate selected using JWST NIRCam/MIRI, mid-IR, sub-mm, and radio imaging in the COSMOS-Web field. Using multi-frequency radio observations and mid-IR photometry, we identify a powerful, radio-loud (RL), growing supermassive black hole (SMBH) with significant spectral steepening of the radio SED ($f_{1.28 \mathrm{GHz}} \sim 2$ mJy, $q_{24μm} = -1.1$, $α_{1.28-3\mathrm{GHz}}=-1.2$, $Δα= -0.4$). In conjunction with ALMA, deep ground-based observations, ancillary space-based data, and the unprecedented resolution and sensitivity of JWST, we find no evidence of AGN contribution to the UV/optical/NIR data and thus infer heavy amounts of obscuration (N$_{\mathrm{H}} > 10^{23}$ cm$^{-2}$). Using the wealth of deep UV to sub-mm photometric data, we report a singular solution photo-z of $z_\mathrm{phot}$ = 7.7$^{+0.4}_{-0.3}$ and estimate an extremely massive host-galaxy ($\log M_{\star} = 11.4 -12\,\mathrm{M}_{\odot}$) hosting a powerful, growing SMBH (L$_{\mathrm{Bol}} = 4-12 \times 10^{46}$ erg s$^{-1}$). This source represents the furthest known obscured RL AGN candidate, and its level of obscuration aligns with the most representative but observationally scarce population of AGN at these epochs.

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arXiv2023

COSMOS-Web: Intrinsically Luminous z$\gtrsim$10 Galaxy Candidates Test Early Stellar Mass Assembly

We report the discovery of 15 exceptionally luminous $10\lesssim z\lesssim14$ candidate galaxies discovered in the first 0.28 deg$^2$ of JWST/NIRCam imaging from the COSMOS-Web Survey. These sources span rest-frame UV magnitudes of $-20.5>M_{\rm UV}>-22$, and thus constitute the most intrinsically luminous $z\gtrsim10$ candidates identified by JWST to-date. Selected via NIRCam imaging with Hubble ACS/F814W, deep ground-based observations corroborate their detection and help significantly constrain their photometric redshifts. We analyze their spectral energy distributions using multiple open-source codes and evaluate the probability of low-redshift solutions; we conclude that 12/15 (80%) are likely genuine $z\gtrsim10$ sources and 3/15 (20%) likely low-redshift contaminants. Three of our $z\sim12$ candidates push the limits of early stellar mass assembly: they have estimated stellar masses $\sim5\times10^{9}\,M_\odot$, implying an effective stellar baryon fraction of $ε_{\star}\sim0.2-0.5$, where $ε_{\star}\equiv M_{\star}/(f_{b}M_{halo})$. The assembly of such stellar reservoirs is made possible due to rapid, burst-driven star formation on timescales $<$100\,Myr where the star-formation rate may far outpace the growth of the underlying dark matter halos. This is supported by the similar volume densities inferred for $M_\star\sim10^{10}\,M_\odot$ galaxies relative to $M_\star\sim10^{9}\,M_\odot$ -- both about $10^{-6}$ Mpc$^{-3}$ -- implying they live in halos of comparable mass. At such high redshifts, the duty cycle for starbursts would be of order unity, which could cause the observed change in the shape of the UVLF from a double powerlaw to Schechter at $z\approx8$. Spectroscopic redshift confirmation and ensuing constraints of their masses will be critical to understanding how, and if, such early massive galaxies push the limits of galaxy formation in $Λ$CDM.

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arXiv2023

Unveiling the distant Universe: Characterizing $z\ge9$ Galaxies in the first epoch of COSMOS-Web

We report the identification of 15 galaxy candidates at $z\ge9$ using the initial COSMOS-Web JWST observations over 77 arcmin$^2$ through four NIRCam filters (F115W, F150W, F277W, F444W) with an overlap with MIRI (F770W) of 8.7 arcmin$^2$. We fit the sample using several publicly-available SED fitting and photometric redshift codes and determine their redshifts between $z=9.3$ and $z=10.9$ ($\langle z\rangle=10.0$), UV-magnitudes between M$_{\rm UV}$ = $-$21.2 and $-$19.5 (with $\langle $M$_{\rm UV}\rangle=-20.2$) and rest-frame UV slopes ($\langle β\rangle=-2.4$). These galaxies are, on average, more luminous than most $z\ge9$ candidates discovered by JWST so far in the literature, while exhibiting similar blue colors in their rest-frame UV. The rest-frame UV slopes derived from SED-fitting are blue ($β\sim$[$-$2.0, $-$2.7]) without reaching extremely blue values as reported in other recent studies at these redshifts. The blue color is consistent with models that suggest the underlying stellar population is not yet fully enriched in metals like similarly luminous galaxies in the lower redshift Universe. The derived stellar masses with $\langle \log_{\rm 10} ($M$_\star/$M$_\odot)\rangle\approx8-9$ are not in tension with the standard $Λ$CDM model and our measurement of the volume density of such UV luminous galaxies aligns well with previously measured values presented in the literature at $z\sim9-10$. Our sample of galaxies, although compact, are significantly resolved.

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arXiv2023

Two massive, compact, and dust-obscured candidate $z\sim 8$ galaxies discovered by JWST

We present a search for extremely red, dust-obscured, $z>7$ galaxies with $\textit{JWST}$/NIRCam+MIRI imaging over the first 20 arcmin$^2$ of publicly-available Cycle 1 data from the COSMOS-Web, CEERS, and PRIMER surveys. Based on their red color in F277W$-$F444W ($\sim 2.5$ mag) and detection in MIRI/F770W ($\sim 25$ mag), we identify two galaxies$\unicode{x2014}$COS-z8M1 and CEERS-z7M1$\unicode{x2014}$which have best-fit photometric redshifts of $z=8.5^{+0.3}_{-0.4}$ and $z=7.6^{+0.1}_{-0.1}$, respectively. We perform SED fitting with a variety of codes (including BAGPIPES, PROSPECTOR, BEAGLE, and CIGALE), and find a $>95\%$ probability that these indeed lie at $z>7$. Both sources are compact ($R_{\rm eff} \lesssim 200$ pc), highly obscured ($A_V \sim 1.5$$\unicode{x2013}$$2.5$), and, at our best-fit redshift estimates, likely have strong [OIII]+H$β$ emission contributing to their $4.4\,μ$m photometry. We estimate stellar masses of $\sim 10^{10}~M_\odot$ for both sources; by virtue of detection in MIRI at $7.7\,μ$m, these measurements are robust to the inclusion of bright emission lines, for example, from an AGN. We identify a marginal (2.9$σ$) ALMA detection at 2 mm within $0.5''$ of COS-z8M1, which if real, would suggest a remarkably high IR luminosity of $\sim 10^{12} L_\odot$. These two galaxies, if confirmed at $z\sim 8$, would be extreme in their stellar and dust masses, and may be representative of a substantial population of modestly dust-obscured galaxies at cosmic dawn.

astro-ph.GA↗

arXiv2023

A Near-Infrared Faint, Far-Infrared-Luminous Dusty Galaxy at z~5 in COSMOS-Web

A growing number of far-infrared bright sources completely invisible in deep extragalactic optical surveys hint at an elusive population of z>4 dusty, star-forming galaxies. Cycle 1 JWST surveys are now detecting their rest-frame optical light, which provides key insight into their stellar properties and statistical constraints on the population as a whole. This work presents the JWST/NIRCam counterpart from the COSMOS-Web survey to a far-infrared SCUBA-2 and ALMA source, AzTECC71, which was previously undetected at wavelengths shorter than 850 microns. AzTECC71, amongst the reddest galaxies in COSMOS-Web with F277W - F444W~0.9, is undetected in NIRCam/F150W and F115W and fainter in F444W than other sub-millimeter galaxies identified in COSMOS-Web by 2-4 magnitudes. This is consistent with the system having both a lower stellar mass and higher redshift than the median dusty, star-forming galaxy. With deep ground- and space-based upper limits combined with detections in F277W, F444W and the far-IR including ALMA Band 6, we find a high probability (99%) that AzTECC71 is at z>4 with z_phot=5.7(+0.8,-0.7). This galaxy is massive (logM*/Msun~10.7) and IR-luminous (logLIR/Lsun~12.7), comparable to other optically-undetected but far-IR bright dusty, star-forming galaxies at z>4. This population of luminous, infrared galaxies at z>4 is largely unconstrained but comprises an important bridge between the most extreme dust-obscured galaxies and more typical high-redshift star-forming galaxies. If further far-IR-selected galaxies that drop out of the F150W filter in COSMOS-Web have redshifts z>4 like AzTECC71, then the volume density of such sources may be ~3-10x greater than previously estimated.

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