arXiv subjects

Karl Glazebrook

Publications and source records attributed to Karl Glazebrook.

At least 109 records · Page 6Linked to original sources

arXiv2023

The UNCOVER Survey: A first-look HST+JWST catalog of 60,000 galaxies near Abell 2744 and beyond

In November 2022, the James Webb Space Telescope (JWST) returned deep near-infrared images of Abell 2744 -- a powerful lensing cluster capable of magnifying distant, incipient galaxies beyond it. Together with the existing Hubble Space Telescope (HST) imaging, this publicly available dataset opens a fundamentally new discovery space to understand the remaining mysteries of the formation and evolution of galaxies across cosmic time. In this work, we detect and measure some 60,000 objects across the 49 arcmin$^2$ JWST footprint down to a $5\,σ$ limiting magnitude of $\sim$30 mag in 0.32" apertures. Photometry is performed using circular apertures on images matched to the point spread function of the reddest NIRCam broad band, F444W, and cleaned of bright cluster galaxies and the related intra-cluster light. To give an impression of the photometric performance, we measure photometric redshifts and achieve a $σ_{\rm NMAD}\approx0.03$ based on known, but relatively small, spectroscopic samples. With this paper, we publicly release our HST and JWST PSF-matched photometric catalog with optimally assigned aperture sizes for easy use, along with single aperture catalogs, photometric redshifts, rest-frame colors, and individual magnification estimates. These catalogs will set the stage for efficient and deep spectroscopic follow-up of some of the first JWST-selected samples in Summer 2023.

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arXiv2023

UNCOVER spectroscopy confirms a surprising ubiquity of AGN in red galaxies at $z>5$

JWST is revealing a new population of dust-reddened broad-line active galactic nuclei (AGN) at redshifts $z\gtrsim5$. Here we present deep NIRSpec/Prism spectroscopy from the Cycle 1 Treasury program UNCOVER of 15 AGN candidates selected to be compact, with red continua in the rest-frame optical but with blue slopes in the UV. From NIRCam photometry alone, they could have been dominated by dusty star formation or AGN. Here we show that the majority of the compact red sources in UNCOVER are dust-reddened AGN: $60\%$ show definitive evidence for broad-line H$α$ with FWHM$\, >2000$ km/s, for $20\%$ current data are inconclusive, and $20\%$ are brown dwarf stars. We propose an updated photometric criterion to select red $z>5$ AGN that excludes brown dwarfs and is expected to yield $>80\%$ AGN. Remarkably, among all $z_{\rm phot}>5$ galaxies with F277W$-$F444W$>1$ in UNCOVER at least $33\%$ are AGN regardless of compactness, climbing to at least $80\%$ AGN for sources with F277W$-$F444W$>1.6$. The confirmed AGN have black hole masses of $10^7-10^9$ M$_{\odot}$. While their UV-luminosities ($-16>M_{\rm UV}>-20$ AB mag) are low compared to UV-selected AGN at these epochs, consistent with percent-level scattered AGN light or low levels of unobscured star formation, the inferred bolometric luminosities are typical of $10^7-10^9$ M$_{\odot}$ black holes radiating at $\sim 10-40\%$ of Eddington. The number densities are surprisingly high at $\sim10^{-5}$ Mpc$^{-3}$ mag$^{-1}$, 100 times more common than the faintest UV-selected quasars, while accounting for $\sim1\%$ of the UV-selected galaxies. While their UV-faintness suggest they may not contribute strongly to reionization, their ubiquity poses challenges to models of black hole growth.

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arXiv2023

Resolved velocity profiles of galactic winds at Cosmic Noon

We study the kinematics of the interstellar medium (ISM) viewed "down the barrel" in 20 gravitationally lensed galaxies during Cosmic Noon ($z=1.5 - 3.5$). We use moderate-resolution spectra ($R\sim4000$) from Keck/ESI and Magellan/MagE to spectrally resolve the ISM absorption in these galaxies into $\sim$10 independent elements and use double Gaussian fits to quantify the velocity structure of the gas. We find that the bulk motion of gas in this galaxy sample is outflowing, with average velocity centroid $\left =-141$ km$\,$s$^{-1}$ ($\pm111$ km$\,$s$^{-1}$ scatter) measured with respect to the systemic redshift. 16 out of the 20 galaxies exhibit a clear positive skewness, with a blueshifted tail extending to $\sim -500$ km$\,$s$^{-1}$. We examine scaling relations in outflow velocities with galaxy stellar mass and star formation rate (SFR), finding correlations consistent with a momentum-driven wind scenario. Our measured outflow velocities are also comparable to those reported for FIRE-2 and TNG50 cosmological simulations at similar redshift and galaxy properties. We also consider implications for interpreting results from lower-resolution spectra. We demonstrate that while velocity centroids are accurately recovered, the skewness, velocity width, and probes of high velocity gas (e.g., $v_{95}$) are subject to large scatter and biases at lower resolution. We find that $R\gtrsim1700$ is required for accurate results for the gas kinematics of our sample. This work represents the largest available sample of well-resolved outflow velocity structure at $z>2$, and highlights the need for good spectral resolution to recover accurate properties.

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arXiv2023

UNCOVER: Candidate Red Active Galactic Nuclei at 3<z<7 with JWST and ALMA

The James Webb Space Telescope (JWST) is revolutionizing our knowledge of $z>5$ galaxies and their actively accreting black holes. Using the JWST Cycle 1 Treasury program Ultradeep NIRSpec and NIRCam ObserVations before the Epoch of Reionization (UNCOVER) in the lensing field Abell 2744, we report the identification of a sample of little red dots at $3 < z_{\rm{phot}} < 7$ that likely contain highly-reddened accreting supermassive black holes. Using a NIRCam-only selection to F444W$<27.7$ mag, we find 26 sources over the $\sim45$ arcmin$^{2}$ field that are blue in F115W$-$F200W$\sim0$ (or $β_{\rm UV}\sim-2.0$ for $f_λ \propto λ^β$), red in F200W$-$F444W = $1-4$ ($β_{\rm opt} \sim +2.0$), and are dominated by a point-source like central component. Of the 20 sources with deep ALMA 1.2-mm coverage, none are detected individually or in a stack. For the majority of the sample, SED fits to the JWST+ALMA observations prefer models with hot dust rather than obscured star-formation to reproduce the red NIRCam colors and ALMA 1.2-mm non-detections. While compact dusty star formation can not be ruled out, the combination of extremely small sizes ($\langle r_e \rangle\approx50$ pc after correction for magnification), red rest-frame optical slopes, and hot dust can by explained by reddened broad-line active galactic nuclei (AGNs). Our targets have faint $M_{\rm 1450} \approx -14\ \, {\rm to} -18$ mag but inferred bolometric luminosities of $L_{\rm bol} = 10^{43}-10^{46}$ erg/s, reflecting their obscured nature. If the candidates are confirmed as AGNs with upcoming UNCOVER spectroscopy, then we have found an abundant population of reddened luminous AGN that are at least ten times more numerous than UV-luminous AGN at the same intrinsic bolometric luminosity.

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arXiv2023

JWST UNCOVER: Extremely red and compact object at$z_{\mathrm{phot}}\simeq7.6$ triply imaged by Abell 2744

Recent JWST/NIRCam imaging taken for the ultra-deep UNCOVER program reveals a very red dropout object at $z_{\mathrm{phot}}\simeq7.6$, triply imaged by the galaxy cluster Abell 2744 ($z_{\mathrm{d}}=0.308$). All three images are very compact, i.e. unresolved, with a de-lensed size upper-limit of $r_{e}\lesssim35$ pc. The images have apparent magnitudes of $m_{\mathrm{F444W}}\sim25-26$ AB, and the magnification-corrected absolute UV magnitude of the source is $M_{\mathrm{UV},1450}=-16.81\pm0.09$. From the sum of observed fluxes and from a spectral energy distribution (SED) analysis, we obtain estimates of the bolometric luminosities of the source of $L_{\mathrm{bol}}\gtrsim10^{43} \frac{\mathrm{erg}}{\mathrm{s}}$ and $L_{\mathrm{bol}}\sim10^{44}-10^{46} \frac{\mathrm{erg}}{\mathrm{s}}$, respectively. Based on its compact, point-like appearance, its position in color-color space and the SED analysis, we tentatively conclude that this object is a UV-faint dust-obscured quasar-like object, i.e. an active galactic nucleus (AGN) at high redshift. We also discuss other alternative origins for the object's emission features, including a massive star cluster, Population III, supermassive, or dark stars, or a direct-collapse black hole. Although populations of red galaxies at similar photometric redshifts have been detected with JWST, this object is unique in that its high-redshift nature is corroborated geometrically by lensing, that it is unresolved despite being magnified -- and thus intrinsically even more compact -- and that it occupies notably distinct regions in both size-luminosity and color-color space. Planned UNCOVER JWST/NIRSpec observations, scheduled in Cycle 1, will enable a more detailed analysis of this object.

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arXiv2023

The GLASS-JWST Early Release Science Program. II. Stage I release of NIRCam imaging and catalogs in the Abell 2744 region

We present images and a multi-wavelength photometric catalog based on all of the JWST NIRCam observations obtained to date in the region of the Abell 2744 galaxy cluster. These data come from three different programs, namely the GLASS-JWST Early Release Science Program, UNCOVER, and Director's Discretionary Time program 2756. The observed area in the NIRCam wide-band filters - covering the central and extended regions of the cluster, as well as new parallel fields - is 46.5 arcmin$^2$ in total. All images in eight bands (F090W, F115W, F150W, F200W, F277W, F356W, F410M, F444W) have been reduced adopting the latest calibration and reference files available. Data reduction has been performed using an augmented version of the official JWST pipeline, with improvements aimed at removing or mitigating defects in the raw images and improving the background subtraction and photometric accuracy. We obtain a F444W-detected multi-band catalog, including all NIRCam and available HST data, adopting forced aperture photometry on PSF-matched images. The catalog is intended to enable early scientific investigations and is optimized for the study of faint galaxies; it contains 24389 sources, with a 5$σ$ limiting magnitude in the F444W band ranging from 28.5 AB to 30.5 AB, as a result of the varying exposure times of the surveys that observed the field. We publicly release the reduced NIRCam images, associated multi-wavelength catalog and code adopted for $1/f$ noise removal with the aim of aiding users to familiarize themselves with JWST NIRCam data and identify suitable targets for follow-up observations.

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arXiv2023

Early Results from GLASS-JWST. XXI: Rapid assembly of a galaxy at z=6.23 revealed by its C/O abundance

The abundance of carbon relative to oxygen (C/O) is a promising probe of star formation history in the early universe, as the ratio changes with time due to production of these elements by different nucleosynthesis pathways. We present a measurement of $\log{\mathrm{(C/O)}} = -1.01\pm0.12$ (stat) $\pm0.15$ (sys) in a $z=6.23$ galaxy observed as part of the GLASS-JWST Early Release Science Program. Notably, we achieve good precision thanks to the detection of the rest-frame ultraviolet O III], C III], and C IV emission lines delivered by JWST/NIRSpec. The C/O abundance is $\sim$0.8 dex lower than the solar value and is consistent with the expected yield from core-collapse supernovae, indicating that longer-lived intermediate mass stars have not fully contributed to carbon enrichment. This in turn implies rapid buildup of a young stellar population with age $\lesssim100$ Myr in a galaxy seen $\sim$900 million years after the Big Bang. Our chemical abundance analysis is consistent with spectral energy distribution modeling of JWST/NIRCam photometric data, which indicates a current stellar mass $\log\,\mathrm{M}_* / \mathrm{M_{sun}} = 8.4^{+0.4}_{-0.2}$ and specific star formation rate sSFR $\simeq 20$ Gyr$^{-1}$. These results showcase the value of chemical abundances and C/O in particular to study the earliest stages of galaxy assembly.

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arXiv2023

The nature of an ultra-faint galaxy in the cosmic Dark Ages seen with JWST

In the first billion years after the Big Bang, sources of ultraviolet (UV) photons are believed to have ionized intergalactic hydrogen, rendering the Universe transparent to UV radiation. Galaxies brighter than the characteristic luminosity $L^{*}$ do not provide enough ionizing photons to drive this cosmic reionization. Fainter galaxies are thought to dominate the photon budget; however they are surrounded by neutral gas that prevents the escape of the Lyman-$α$ photons, which has been the dominant way to identify them so far. JD1 was previously identified as a triply-imaged galaxy with a magnification factor of 13 provided by the foreground cluster Abell 2744, and a photometric redshift of $z\sim10$. Here we report the spectroscopic confirmation of this very low luminosity ($\sim0.05 L^{*}$) galaxy at $z=9.79$, observed 480 Myr after the Big Bang, by means of the identification of the Lyman break and redward continuum, as well as multiple $\gtrsim4σ$ emission lines, with the Near-InfraRed Spectrograph (NIRSpec) and Near-InfraRed Camera (NIRCam) instruments. The combination of the James Webb Space Telescope (JWST) and gravitational lensing shows that this ultra-faint galaxy ($M_{\rm UV}=-17.35$) -- with a luminosity typical of the sources responsible for cosmic reionization -- has a compact ($\sim$150 pc) and complex morphology, low stellar mass (10$^{7.19}$ M$_\odot$), and subsolar ($\sim$0.6 $Z_{\odot}$) gas-phase metallicity.

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arXiv2023

KURVS: The outer rotation curve shapes and dark matter fractions of $z \sim 1.5 $ star-forming galaxies

We present first results from the KMOS Ultra-deep Rotation Velocity Survey (KURVS), aimed at studying the outer rotation curves shape and dark matter content of 22 star-forming galaxies at $z\sim1.5$. These galaxies represent `typical' star-forming discs at $z \sim 1.5$, being located within the star-forming main sequence and stellar mass-size relation with stellar masses $9.5\leqslant$log$(M_{\star}/\mathrm{M_{\odot}})\leqslant11.5$. We extract individual rotation curves out to 4 times the effective radius, on average, or $\sim 10-15$ kpc. Most rotation curves are flat or rising between three- and six-disc scale radii. Only three objects with dispersion-dominated dynamics ($v_{\rm rot}/σ_0\sim0.2$) have declining outer rotation curves at more than 5$σ$ significance. After accounting for seeing and pressure support, the nine rotation-dominated discs with $v_{\rm rot}/σ_0\geqslant1.5$ have average dark matter fractions of $50 \pm 20\%$ at the effective radius, similar to local discs. Together with previous observations of star-forming galaxies at cosmic noon, our measurements suggest a trend of declining dark matter fraction with increasing stellar mass and stellar mass surface density at the effective radius. Simulated EAGLE galaxies are in quantitative agreement with observations up to log$(M_{\star}R_{\rm eff}^{-2}/\mathrm{M_{\odot}kpc^{-2}}) \sim 9.2$, and over-predict the dark matter fraction of galaxies with higher mass surface densities by a factor of $\sim 3$. We conclude that the dynamics of typical rotationally-supported discs at $z \sim 1.5$ is dominated by dark matter from effective radius scales, in broad agreement with cosmological models. The tension with observations at high stellar mass surface density suggests that the prescriptions for baryonic processes occurring in the most massive galaxies (such as bulge growth and quenching) need to be reassessed.

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arXiv2023

The impact of human expert visual inspection on the discovery of strong gravitational lenses

We investigate the ability of human 'expert' classifiers to identify strong gravitational lens candidates in Dark Energy Survey like imaging. We recruited a total of 55 people that completed more than 25$\%$ of the project. During the classification task, we present to the participants 1489 images. The sample contains a variety of data including lens simulations, real lenses, non-lens examples, and unlabeled data. We find that experts are extremely good at finding bright, well-resolved Einstein rings, whilst arcs with $g$-band signal-to-noise less than $\sim$25 or Einstein radii less than $\sim$1.2 times the seeing are rarely recovered. Very few non-lenses are scored highly. There is substantial variation in the performance of individual classifiers, but they do not appear to depend on the classifier's experience, confidence or academic position. These variations can be mitigated with a team of 6 or more independent classifiers. Our results give confidence that humans are a reliable pruning step for lens candidates, providing pure and quantifiably complete samples for follow-up studies.

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arXiv2023

Early results from GLASS-JWST. XIV: A spectroscopically confirmed protocluster 650 million years after the Big Bang

We present the spectroscopic confirmation of a protocluster at $z=7.88$ behind the galaxy cluster Abell2744 (hereafter A2744-z7p9OD). Using JWST NIRSpec, we find seven galaxies within a projected radius of 60kpc. Although the galaxies reside in an overdensity around $>20\times$ greater than a random volume, they do not show strong Lyman-alpha emission. We place 2-$σ$ upper limits on the rest-frame equivalent width $<16$-$28$AA. Based on the tight upper limits to the Lyman-alpha emission, we constrain the volume-averaged neutral fraction of hydrogen in the intergalactic medium to be $x_{\rm HI} > 0.45$ (68% CI). Using an empirical $M_{\rm UV}$-$M_{\rm halo}$ relation for individual galaxies, we estimate that the total halo mass of the system is $\gtrsim 4\times10^{11}\,M_\odot$. Likewise, the line of sight velocity dispersion is estimated to be $1100 \pm 200$km/s. Using an empirical relation, we estimate the present-day halo mass of A2744-z7p9OD to be $\sim2\times10^{15}\,M_\odot$, comparable to the Coma cluster. A2744-z7p9OD is the highest redshift spectroscopically confirmed protocluster to date, demonstrating the power of JWST to investigate the connection between dark-matter halo assembly and galaxy formation at very early times with medium-deep observations at $<20$hrs total exposure time. Follow-up spectroscopy of the remaining photometric candidates of the overdensity will further refine the features of this system and help characterize the role of such overdensities in cosmic reionization.

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arXiv2023

Early Results from GLASS-JWST. XIX: A High Density of Bright Galaxies at $z\approx10$ in the Abell 2744 Region

We report the detection of a high density of redshift $z\approx 10$ galaxies behind the foreground cluster Abell 2744, selected from imaging data obtained recently with NIRCam onboard {\it JWST} by three programs -- GLASS-JWST, UNCOVER, and DDT\#2756. To ensure robust estimates of the lensing magnification $μ$, we use an improved version of our model that exploits the first epoch of NIRCam images and newly obtained MUSE spectra, and avoids regions with $μ>5$ where the uncertainty may be higher. We detect seven bright $z\approx 10$ galaxies with demagnified rest-frame $-22 \lesssim M_{\rm UV}\lesssim -19$ mag, over an area of $\sim37$ sq. arcmin. Taking into account photometric incompleteness and the effects of lensing on luminosity and cosmological volume, we find that the density of $z\approx 10$ galaxies in the field is about $10\times$ ($3\times$) larger than the average at $M_{UV}\approx -21~ (-20)$ mag reported so far. The density is even higher when considering only the GLASS-JWST data, which are the deepest and the least affected by magnification and incompleteness. The GLASS-JWST field contains 5 out of 7 galaxies, distributed along an apparent filamentary structure of 2 Mpc in projected length, and includes a close pair of candidates with $M_{\rm UV}< -20$ mag having a projected separation of only 16 kpc. These findings suggest the presence of a $z\approx 10$ overdensity in the field. In addition to providing excellent targets for efficient spectroscopic follow-up observations, our study confirms the high density of bright galaxies observed in early {\it JWST} observations, but calls for multiple surveys along independent lines of sight to achieve an unbiased estimate of their average density and a first estimate of their clustering.

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arXiv2023

Early results from GLASS-JWST XIV: A first morphological atlas of the 1 < z < 5 Universe in the rest-frame optical

We present a rest-frame optical morphological analysis of galaxies observed with the NIRCam imager on the James Webb Space Telescope (JWST) as part of the GLASS-JWST Early Release Science program. We select 388 sources at redshifts $0.8 < z < 5.4$ and use the seven 0.9--5\micron\ NIRCam filters to generate rest-frame $gri$ composite color images, and conduct visual morphological classification. Compared to HST-based work we find a higher incidence of disks and bulges than expected at $z>1.5$, revealed by rest frame optical imaging. We detect 123 clear disks (58 at $z>1.5$) of which 76 have bulges. No evolution of bulge fraction with redshift is evident: 61\% at $z<2$ ($N=110$) versus 60\% at $z\geq2$ ($N=13$). A stellar mass dependence is evident, with bulges visible in 80\% of all disk galaxies with mass $> 10^{9.5}\, {\rm M}_{\odot}$ ($N=41$) but only 52\% at $M < 10^{9.5}\, {\rm M}_{\odot}$ ($N=82$). We supplement visual morphologies with non-parametric measurements of Gini and Asymmetry coefficients in the rest-frame $i$-band. Our sources are more asymmetric than local galaxies, with slightly higher Gini values. When compared to high-z rest-frame ultraviolet measurements with Hubble Space Telescope, JWST shows more regular morphological types such as disks, bulges and spiral arms at $z>1.5$, with smoother (i.e. lower Gini) and more symmetrical light distributions.

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arXiv2023

Early results from GLASS-JWST. XX: Unveiling a population of "red-excess'' galaxies in Abell2744 and in the coeval field

We combine JWST/NIRCam imaging and MUSE data to characterize the properties of galaxies in different environmental conditions in the cluster Abell2744 ($z=0.3064$) and in its immediate surroundings. We investigate how galaxy colors, morphology and star forming fractions depend on wavelength and on different parameterizations of environment. Our most striking result is the discovery of a ``red-excess'' population in F200W$-$F444W colors both in the cluster regions and the field. These galaxies have normal F115W$-$F150W colors, but are up to 0.8 mag redder than red sequence galaxies in F200W$-$F444W. They also have rather blue rest frame B$-$V colors. {Galaxies in the field and at the cluster virial radius are overall characterized by redder colors, but galaxies with the largest color deviations are found in the field and in the cluster core. Several results} suggest that mechanisms taking place in these regions might be more effective in producing these colors. Looking at their morphology, many cluster galaxies show signatures consistent with ram pressure stripping, while field galaxies have features resembling interactions and mergers. Our hypothesis is that these galaxies are characterized by dust enshrouded star formation: a JWST/NIRSpec spectrum for one of the galaxies is dominated by a strong PAH at 3.3$μm$, suggestive of dust obscured star formation. Larger spectroscopic samples are needed to understand if the color excess is due exclusively to dust-obscured star formation, and the role of environment in triggering it.

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arXiv2023

A Glimpse of the Stellar Populations and Elemental Abundances of Gravitationally Lensed, Quiescent Galaxies at $z\gtrsim 1$ with Keck Deep Spectroscopy

Gravitational lenses can magnify distant galaxies, allowing us to discover and characterize the stellar populations of intrinsically faint, quiescent galaxies that are otherwise extremely difficult to directly observe at high redshift from ground-based telescopes. Here, we present the spectral analysis of two lensed, quiescent galaxies at $z\gtrsim 1$ discovered by the ASTRO 3D Galaxy Evolution with Lenses survey: AGEL1323 ($M_*\sim 10^{11.1}M_{\odot}$, $z=1.016$, $μ\sim 14.6$) and AGEL0014 ($M_*\sim 10^{11.5}M_{\odot}$, $z=1.374$, $μ\sim 4.3$). We measured the age, [Fe/H], and [Mg/Fe] of the two lensed galaxies using deep, rest-frame-optical spectra (S/N $\gtrsim 40$~$\mathring {\mathrm A}$$^{-1}$) obtained on the Keck~I telescope. The ages of AGEL1323 and AGEL0014 are $5.6^{+0.8}_{-0.8}$~Gyr and $3.1^{+0.8}_{-0.3}$~Gyr, respectively, indicating that most of the stars in the galaxies were formed less than 2~Gyr after the Big Bang. Compared to nearby quiescent galaxies of similar masses, the lensed galaxies have lower [Fe/H] and [Mg/H]. Surprisingly, the two galaxies have comparable [Mg/Fe] to similar-mass galaxies at lower redshifts, despite their old ages. Using a simple analytic chemical evolution model connecting the instantaneously recycled element Mg with the mass-loading factors of outflows averaged over the entire star formation history, we found that the lensed galaxies may have experienced enhanced outflows during their star formation compared to lower-redshift galaxies, which may explain why they quenched early.

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arXiv2023

Early results from GLASS-JWST XVI: Discovering a bluer z~4-7 Universe through UV slopes

We use the GLASS-JWST Early Release Science NIRCam parallel observations to provide a first view of the UV continuum properties of NIRCam/F444W selected galaxies at 4 99% of the galaxies are blue star-forming galaxies with very low levels of dust (Avbeta~0.01+/-0.33). We find no statistically significant correlation for UV slope with redshift or UV magnitude. However, we find that in general galaxies at higher redshifts and fainter UV magnitudes have steeper UV slopes. We find a statistically significant correlation for UV slope with stellar mass, with galaxies with higher stellar mass showing shallower UV slopes. Individual fits to some of our galaxies reach the bluest UV slopes of beta~-3.1 allowed by stellar population models used in this analysis. Therefore, it is likely that stellar population models with higher amount of Lyman continuum leakage, AGN effects, and/or Population III contributions are required to accurately reproduce the rest-UV and optical properties of some of our bluest galaxies. This dust-free early view confirms that our current cosmological understanding of gradual mass + dust buildup of galaxies with cosmic time is largely accurate to describe the ~0.7-1.5 Gyr age window of the Universe. The abundance of a large population of UV faint dust-poor systems may point to a dominance of low-mass galaxies at z>6 playing a vital role in cosmic reionization.

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arXiv2023

Early results from GLASS-JWST XV: properties of the faintest red sources in the NIRCAM deep fields

We present a first look at the reddest 2-5$μ\rm m$ sources found in deep images from the GLASS Early Release Science program. We undertake a general search, i.e. not looking for any particular spectral signatures, for sources detected only in bands redder than reachable with the Hubble Space Telescope, and which would likely not have been identified in pre-JWST surveys. We search for sources down to AB $\sim 27$ (corresponding to $>10σ$ detection threshold) in any of the F200W to F444W filters,with a $>1$ magnitude excess relative to F090W to F150W bands. Fainter than F444W$>25$ we find 56 such sources of which 37 have reasonably constrained spectral energy distributions to which we can fit photometric redshifts. We find the majority of this population ($\sim$ 65%) as $2 $2$μ\rm m$ boosted by a combination of the Balmer break and emission lines. The typical implied rest equivalent widths are $\sim200\unicode{0x212B}$ with some extreme objects up to $\sim 1000\unicode{0x212B}$. This is in contrast with brighter magnitudes where the red sources tend to be $z<3$ quiescent galaxies and dusty star forming objects. Our general selection criteria for red sources allow us to independently identify other phenomena as diverse as extremely low mass ($\sim 10^8$ M$_\odot$) quiescent galaxies at $z<1$, recover recently identified $z>11$ galaxies and a very cool brown dwarf.

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arXiv2023

Deep ALMA redshift search of a z~12 GLASS-JWST galaxy candidate

The James Webb Space Telescope (JWST) has discovered a surprising abundance of bright galaxy candidates in the very early Universe ($< 500$ Myrs after the Big Bang), calling into question current galaxy formation models. Spectroscopy is needed to confirm the primeval nature of these candidates, as well as to understand how the first galaxies form stars and grow. Here we present deep spectroscopic and continuum ALMA observations towards GHZ2/GLASS-z12, one of the brightest and most robust candidates at $z > 10$ identified in the GLASS-JWST Early Release Science Program. We detect a $5.8 σ$ line, offset 0.5" from the JWST position of GHZ2/GLASS-z12 that, associating it with the [OIII] 88 micron transition, implies a spectroscopic redshift of $z = 12.117 \pm 0.001$. We verify the detection using extensive statistical tests. The oxygen line luminosity places GHZ2/GLASS-z12 above the [OIII]-SFR relation for metal-poor galaxies, implying an enhancement of [OIII] emission in this system while the JWST-observed emission is likely a lower-metallicity region. The lack of dust emission seen by these observations is consistent with the blue UV slope observed by JWST, which suggest little dust attenuation in galaxies at this early epoch. Further observations will unambiguously confirm the redshift and shed light on the origins of the wide and offset line and physical properties of this early galaxy. This work illustrates the synergy between JWST and ALMA and paves the way for future spectroscopic surveys of $z > 10$ galaxy candidates.

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