arXiv subjects

Pieter van Dokkum

Publications and source records attributed to Pieter van Dokkum.

At least 73 records · Page 4Linked to original sources

arXiv2024

FRESCO: The Paschen-$α$ Star Forming Sequence at Cosmic Noon

We present results from the JWST First Reionization Epoch Spectroscopically Complete Observations survey (FRESCO) on the star forming sequence of galaxies at $1.0 9.5 M_\odot$ that are lower than found in many earlier studies by up to 0.6 dex, but in good agreement with recent results obtained with the Prospector fitting framework. The difference log(SFR(Pa$α$)-SFR(Prospector)) is -0.09 $\pm$ 0.04 dex at $10^{10-11} M_\odot$. We also measure the empirical relation between Paschen-$α$ luminosity and rest-frame H band magnitude and find that the scatter is only 0.04 dex lower than that of the SFR-M* relation and is much lower than the systematic differences among relations in the literature due to various methods of converting observed measurements to physical properties. We additionally identify examples of sources -- that, with standard cutoffs via the UVJ diagram, would be deemed quiescent -- with significant, typically extended, Paschen-$α$ emission. Our results may be indicative of the potential unification of methods used to derive the star forming sequence with careful selection of star forming galaxies and independent star formation rate and stellar mass indicators.

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arXiv2024

First Results from the Dragonfly Ultrawide Survey: the Largest Eleven Quenched Diffuse Dwarf Galaxies in 3100 deg$^2$ with Spectroscopic Confirmation

The Dragonfly Telephoto Array employs a unique design to detect very large and diffuse galaxies, which might be missed with conventional telescopes. The Dragonfly Ultrawide Survey (DFUWS) is a new wide-field survey which will cover 10,000 deg$^2$ of the northern sky, and it provides an ideal dataset to find these large diffuse galaxies. From 3100 deg$^2$ of DFUWS data, we identified eleven large, low surface brightness galaxies as a pilot sample for spectroscopic follow-up. These are the largest galaxies in the examined area that appear smooth and isolated, with effective radii of 12"-27". Eight are below 24 $\mathrm{mag\,arcsec^{-2}}$ in central $g$-band surface brightness. Keck Cosmic Web Imager (KCWI) spectra of the diffuse light show that all eleven galaxies in this sample are quiescent, and seven qualify as ultra-diffuse galaxies (UDGs). Eight galaxies have distances between 15 and 30 Mpc, while the other three are in the Pegasus cluster at 50 Mpc. Their spectra show evidence of a $\sim 1$Gyr old stellar population in addition to an even older stellar population. The intermediate-age component is present in group and satellite galaxies but not in the Pegasus cluster UDGs. All galaxies in this sample are detected in both Dragonfly and Legacy imaging, and the sample partially overlaps with existing UDG catalogs. This pilot sample provides an excellent training set for our analysis of the upcoming full 10,000 deg$^2$ DFUWS data, from which we may expect to discover even larger, previously-unknown galaxies.

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arXiv2024

Realizing the potential of the Dragonfly Spectral Line Mapper: Calibration methods and on-sky performance

The Dragonfly Spectral Line Mapper is an innovative all-refracting telescope designed to carry out ultra-low surface brightness wide-field mapping of visible wavelength line emission. Equipped with ultranarrowband (0.8 nm bandwidth) filters mounted in Dragonfly Filter-Tilter instrumentation, the Dragonfly Spectral Line Mapper maps H$α$, [NII]$λ$6583, and [OIII]$λ$5007 line emission produced by structures with sizes ranging from $\sim$1 to 1000 kpc in the local Universe. These spatial scales encompass that of the exceedingly diffuse and faintly radiating circumgalactic medium, which is singularly difficult to detect with conventional mirror-based telescope instrumentation. Extremely careful control of systematics is required to directly image these large scale structures, necessitating high fidelity sky background subtraction, wavelength calibration, and specialized flat-fielding methods. In this paper, we discuss the on-sky performance of the Dragonfly Spectral Line Mapper with these methods in place.

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arXiv2024

The Dragonfly Spectral Line Mapper: Completion of the 120-lens array

The Dragonfly Spectral Line Mapper is a mosaic telescope comprising 120 Canon telephoto lenses, based on the design of the Dragonfly Telephoto Array. With a wide field of view, and the addition of the "Dragonfly Filter-Tilter" instrumentation holding ultra narrow bandpass filters in front of each lens, the Dragonfly Spectral Line mapper is optimized for ultra low surface brightness imaging of visible wavelength line emission. The Dragonfly Spectral Line Mapper was constructed and commissioned in four phases from March 2022 to November 2023. During this time, four individual mounts of 30 lenses each were constructed and commissioned. The commissioning of the telescope included the deployment of the "Dragonfly StarChaser" which carries out image stabilization corrections in the telephoto lens, to enable hour-long exposures to be taken. In addition, we introduced new instrumentation such as a film to cover the optics to keep the filters clean. Here we describe the updated design of the complete 120-lens array, and the implementation of the instrumentation described above. Additionally, we present updated characterization of the cameras and filter transmission for the full array. Finally, we reflect on the construction and commissioning process of the complete 120-lens array Dragonfly Spectral Line Mapper, and remark on the feasibility of a larger 1000-lens array.

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arXiv2024

RUBIES: Evolved Stellar Populations with Extended Formation Histories at $z \sim 7-8$ in Candidate Massive Galaxies Identified with JWST/NIRSpec

The identification of red, apparently massive galaxies at $z>7$ in early JWST photometry suggests a strongly accelerated timeline compared to standard models of galaxy growth. A major uncertainty in the interpretation is whether the red colors are caused by evolved stellar populations, dust, or other effects such as emission lines or AGN. Here we show that three of the massive galaxy candidates at $z=6.7-8.4$ have prominent Balmer breaks in JWST/NIRSpec spectroscopy from the RUBIES program. The Balmer breaks demonstrate unambiguously that stellar emission dominates at $λ_{\rm rest} = 0.4\,μ$m, and require formation histories extending hundreds of Myr into the past in galaxies only 600--800 Myr after the Big Bang. Two of the three galaxies also show broad Balmer lines, with H$β$ FWHM $>2500~{\rm km\,s^{-1}}$, suggesting that dust-reddened AGN contribute to, or even dominate, the SEDs of these galaxies at $λ_{\rm rest}\gtrsim 0.6\,μ$m. All three galaxies have relatively narrow [O III] lines, seemingly ruling out a high-mass interpretation if the lines arise in dynamically-relaxed, inclined disks. Yet, the inferred masses also remain highly uncertain. We model the high-quality spectra using Prospector to decompose the continuum into stellar and AGN components, and explore limiting cases in stellar/AGN contribution. This produces a wide range of possible stellar masses, spanning $M_\star \sim 10^9 - 10^{11}\,{\rm M_{\odot}}$. Nevertheless, all fits suggest a very early and rapid formation, most of which follow with a truncation in star formation. Potential origins and evolutionary tracks for these objects are discussed, from the cores of massive galaxies to low-mass galaxies with over-massive black holes. Intriguingly, we find all of these explanations to be incomplete; deeper and redder data are needed to understand the physics of these systems.

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arXiv2024

Deep HST/UVIS imaging of the candidate dark galaxy CDG-1

CDG-1 is a tight grouping of four likely globular clusters in the Perseus cluster, and a candidate dark galaxy with little or no diffuse light. Here we provide new constraints on the luminosity of any underlying stellar emission, using HST/UVIS F200LP imaging. No diffuse emission is detected, with a 2$σ$ upper limit of F200LP>28.1 mag/arcsec$^2$ on the 5'' scale of CDG-1. This surface brightness limit corresponds to a 2$σ$ lower limit of >0.5 for the fraction of the total luminosity that is in the form of globular clusters. The most likely alternative, although improbable, is that CDG-1 is a chance grouping of four globular clusters in the halo of the Perseus galaxy IC312.

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arXiv2024

Analysis of Galaxies at the Extremes: A Kinematic Analysis of the Virgo Cluster Dwarfs VCC 9 and VCC 1448 using the Keck Cosmic Web Imager

We present spatially resolved Keck Cosmic Web Imager stellar spectroscopy of the Virgo cluster dwarf galaxies VCC 9 and VCC 1448. These galaxies have similar stellar masses and large half-light radii but very different globular cluster (GC) system richness ($\sim$25 vs. $\sim$99 GCs). Using the KCWI data, we spectroscopically confirm 10 GCs associated with VCC 1448 and one GC associated with VCC 9. We make two measurements of dynamical mass for VCC 1448 based on the stellar and GC velocities respectively. VCC 1448's mass measurements suggest that it resides in a halo in better agreement with the expectation of the stellar mass -- halo mass relationship than the expectation from its large GC counts. For VCC 9, the dynamical mass we measure agrees with the expected halo mass from both relationships. We compare VCC 1448 and VCC 9 to the GC-rich galaxy Dragonfly 44 ($\sim74$ GCs), which is similar in size but has $\sim 1$ dex less stellar mass than either Virgo galaxy. In dynamical mass -- GC number space, Dragonfly 44 and VCC 1448 exhibit richer GC systems given their dynamical mass than that of VCC 9 and other `normal' galaxies. We also place the galaxies in kinematics -- ellipticity space finding evidence of an anticorrelation between rotational support and the fraction of a galaxy's stellar mass in its GC system. i.e., VCC 9 is more rotationally supported than VCC 1448, which is more rotationally supported than Dragonfly 44. This trend may be expected if a galaxy's GC content depends on its natal gas properties at formation.

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arXiv2024

3D-DASH: The Evolution of Size, Shape, and Intrinsic Scatter in Populations of Young and Old Quiescent Galaxies at 0.5 < z < 3

We present a study of the growth of the quiescent galaxy population between 0.5 < z < 3 by tracing the number density and structural evolution of a sample of 4518 old and 583 young quiescent galaxies with log($M_*$/$M_{\odot}$)>10.4, selected from the COSMOS2020 catalog with complementary HST/F160W imaging from the 3D-DASH survey. Among the quiescent population at z$\sim$2, roughly 50% are recently quenched galaxies; these young quiescent galaxies become increasingly rare towards lower redshift, supporting the idea that the peak epoch of massive galaxy quenching occurred at z>2. Our data show that while the effective half-light radii of quiescent galaxies generally increases with time, young quiescent galaxies are significantly smaller than their older counterparts at the same redshift. In this work we investigate the connection between this size difference and other structural properties, including axis ratios, color gradients, stellar mass, and the intrinsic scatter in effective radii. We demonstrate that the size difference is driven by the most massive sub-population (log($M_*$/$M_{\odot}$)>11) and does not persist when restricting the sample to intermediate mass galaxies (10.4<log($M_*$/$M_{\odot}$)<11). Interestingly, the intrinsic scatter in physical size shows a strong co-evolution over the investigated time period and peaks around z$\sim$2 for both populations, only diverging at z < 1. Taken together, and assuming we are not missing a significant population of lower surface brightness galaxies, while the formation and quenching mechanisms that dominate at higher redshifts yield compact remnants, multiple evolutionary pathways may explain the diverse morphologies of galaxies that quench at z<1.

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arXiv2024

UNCOVER NIRSpec/PRISM Spectroscopy Unveils Evidence of Early Core Formation in a Massive, Centrally Dusty Quiescent Galaxy at $z_{spec}=3.97$

We report the spectroscopic confirmation of a massive ($\log(M_\star/M_\odot)=10.34 \pm_{0.07}^{0.06}$), HST-dark ($m_\mathrm{F150W} - m_\mathrm{F444W} = 3.6$) quiescent galaxy at $z_{spec}=3.97$ in the UNCOVER survey. NIRSpec/PRISM spectroscopy and a non-detection in deep ALMA imaging surprisingly reveals that the galaxy is consistent with a low ($<$10 $M_\odot \ \mathrm{yr^{-1}}$) star formation rate despite evidence for moderate dust attenuation. The F444W image is well modeled with a two component \sersic fit that favors a compact, $r_e\sim200$ pc, $n\sim2.9$ component and a more extended, $r_e\sim1.6$ kpc, $n\sim1.7$ component. The galaxy exhibits strong color gradients: the inner regions are significantly redder than the outskirts. Spectral energy distribution models that reproduce both the red colors and low star formation rate in the center of UNCOVER 18407 require both significant ($A_v\sim1.4$ mag) dust attenuation and a stellar mass-weighted age of 900 Myr, implying 50\% of the stars in the core already formed by $z=7.5$. Using spatially resolved annular mass-to-light measurements enabled by the galaxy's moderate magnification ($μ=2.12\pm_{0.01}^{0.05}$) to reconstruct a radial mass profile from the best-fitting two-component \sersic model, we infer a total mass-weighted $r_\mathrm{eff} = 0.72 \pm_{0.11}^{0.15}$ kpc and log$(Σ_\mathrm{1 kpc} \ [\mathrm{M_\odot/kpc^2}]) = 9.61 \pm_{0.10}^{0.08}$. The early formation of a dense, low star formation rate, and dusty core embedded in a less attenuated stellar envelope suggests an evolutionary link between the earliest-forming massive galaxies and their elliptical descendants. Furthermore, the disparity between the global, integrated dust properties and the spatially resolved gradients highlights the importance of accounting for radially varying stellar populations when characterizing the early growth of galaxy structure.

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arXiv2024

Most of the photons that reionized the Universe came from dwarf galaxies

The identification of sources driving cosmic reionization, a major phase transition from neutral Hydrogen to ionized plasma around 600-800 Myr after the Big Bang (Dayal et al. 2018, Mason et al. 2019, Robertson et al. 2022), has been a matter of intense debate (Robertson et al. 2022). Some models suggest that high ionizing emissivity and escape fractions ($f_{\rm esc}$) from quasars support their role in driving cosmic reionization (Madau & Haardt 2015, Mitra et al. 2018). Others propose that the high $f_{\rm esc}$ values from bright galaxies generates sufficient ionizing radiation to drive this process (Naidu et al. 2020). Finally, a few studies suggest that the number density of faint galaxies, when combined with a stellar-mass-dependent model of ionizing efficiency and $f_{\rm esc}$, can effectively dominate cosmic reionization (Finkelstein et al. 2019, Dayal et al. 2020). However, so far, low-mass galaxies have eluded comprehensive spectroscopic studies owing to their extreme faintness. Here we report an analysis of eight ultra-faint galaxies (in a very small field) during the epoch of reionization with absolute magnitudes between $M_{\rm UV}$ $\sim -17$ to $-15$ mag (down to 0.005 $L^{\star}$. We find that faint galaxies during the Universe's first billion years produce ionizing photons with log($ξ_{\mathrm{ion}}$/ Hz erg$^{-1}$) =$25.80\pm 0.14$, a factor of 4 higher than commonly assumed values (Robertson et al. 2015). If this field is representative of the large scale distribution of faint galaxies, the rate of ionizing photons exceeds that needed for reionization, even for escape fractions of order five per cent.

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arXiv2024

Medium Bands, Mega Science: a JWST/NIRCam Medium-Band Imaging Survey of Abell 2744

In this paper, we describe the "Medium Bands, Mega Science" JWST Cycle 2 survey (JWST-GO-4111) and demonstrate the power of these data to reveal both the spatially-integrated and spatially-resolved properties of galaxies from the local universe to the era of cosmic dawn. Executed in November 2023, MegaScience obtained ~30 arcmin^2 of deep multiband NIRCam imaging centered on the z~0.3 Abell 2744 cluster, including eleven medium-band filters and the two shortest-wavelength broad-band filters, F070W and F090W. Together, MegaScience and the UNCOVER Cycle 1 treasury program provide a complete set of deep (~28-30 mag) images in all NIRCam medium- and broad-band filters. This unique dataset allows us to precisely constrain photometric redshifts, map stellar populations and dust attenuation for large samples of distant galaxies, and examine the connection between galaxy structures and formation histories. MegaScience also includes ~17 arcmin^2 of NIRISS parallel imaging in two broad-band and four medium-band filters from 0.9-4.8um, expanding the footprint where robust spectral energy distribution (SED) fitting is possible. We provide example SEDs and multi-band cutouts at a variety of redshifts, and use a catalog of JWST spectroscopic redshifts to show that MegaScience improves both the scatter and catastrophic outlier rate of photometric redshifts by factors of 2-3. Additionally, we demonstrate the spatially-resolved science enabled by MegaScience by presenting maps of the [OIII] line emission and continuum emission in three spectroscopically-confirmed z>6 galaxies. We show that line emission in reionization-era galaxies can be clumpy, extended, and spatially offset from continuum emission, implying that galaxy assembly histories are complex even at these early epochs. We publicly release fully reduced mosaics and photometric catalogs for both the NIRCam primary and NIRISS parallel fields.

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arXiv2024

The UNCOVER Survey: A First-look HST+JWST Catalog of Galaxy Redshifts and Stellar Population Properties Spanning $0.2 \lesssim z \lesssim 15$

The recent UNCOVER survey with the James Webb Space Telescope (JWST) exploits the nearby cluster Abell 2744 to create the deepest view of our universe to date by leveraging strong gravitational lensing. In this work, we perform photometric fitting of more than 50,000 robustly detected sources out to $z \sim 15$. We show the redshift evolution of stellar ages, star formation rates, and rest-frame colors across the full range of $0.2 \lesssim z \lesssim 15$. The galaxy properties are inferred using the Prospector Bayesian inference framework using informative Prospector-$β$ priors on masses and star formation histories to produce joint redshift and stellar population posteriors, and additionally lensing magnification is performed on-the-fly to ensure consistency with the scale-dependent priors. We show that this approach produces excellent photometric redshifts with $σ_{\rm NMAD} \sim 0.03$, of a similar quality to the established photometric redshift code EAzY. In line with the open-source scientific objective of the Treasury survey, we publicly release the stellar population catalog with this paper, derived from the photometric catalog adapting aperture sizes based on source profiles. This release includes posterior moments, maximum-likelihood spectra, star-formation histories, and full posterior distributions, offering a rich data set to explore the processes governing galaxy formation and evolution over a parameter space now accessible by JWST.

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arXiv2024

UNCOVER: JWST Spectroscopy of Three Cold Brown Dwarfs at Kiloparsec-scale Distances

We report JWST/NIRSpec spectra of three distant T-type brown dwarfs identified in the Ultradeep NIRSpec and NIRCam ObserVations before the Epoch of Reionization (UNCOVER) survey of the Abell 2744 lensing field. One source was previously reported as a candidate T dwarf on the basis of NIRCam photometry, while two sources were initially identified as candidate active galactic nuclei. Low-resolution 1--5 $μ$m spectra confirm the presence of molecular features consistent with T dwarf atmospheres, and comparison to spectral standards infers classifications of sdT1, T6, and T8--T9. The warmest source, UNCOVER-BD-1, shows evidence of subsolar metallicity, and atmosphere model fits indicates T$_{eff}$ = 1300 K and [M/H] $\sim$ $-$1.0, making this one of the few spectroscopically-confirmed T subdwarfs known. The coldest source, UNCOVER-BD-3, is near the T/Y dwarf boundary with T$_{eff}$ = 550 K, and our analysis indicates the presence of PH$_3$ in the 3--5~$μ$m region, favored over CO$_2$ and a possible indicator of subsolar metallicity. We estimate distances of 0.9--4.5 kpc from the Galactic midplane, making these the most distant brown dwarfs with spectroscopic confirmation. Population simulations indicate high probabilities of membership in the Galactic thick disk for two of these brown dwarfs, and potential halo membership for UNCOVER-BD-1. Our simulations indicate that there are approximately 5 T dwarfs and 1--2 L dwarfs in the Abell 2744 field down to F444W = 30 AB mag, roughly one-third of which are thick disk members. These results highlight the utility of deep JWST/NIRSpec spectroscopy for identifying and characterizing the oldest metal-poor brown dwarfs in the Milky Way.

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arXiv2024

A robust and simple method for filling in masked data in astronomical images

Astronomical images often have regions with missing or unwanted information, such as bad pixels, bad columns, cosmic rays, masked objects, or residuals from imperfect model subtractions. In certain situations it can be essential, or preferable, to fill in these regions. Most existing methods use low order interpolations for this task. In this paper a method is described that uses the full information that is contained in the pixels just outside masked regions. These edge pixels are extrapolated inwards, using iterative median filtering. This leads to a smoothly varying spatial resolution within the filled-in regions, and ensures seamless transitions between masked pixels and good pixels. Gaps in continuous, narrow features can be reconstructed with high fidelity, even if they are large. The method is implemented in maskfill, an open-source MIT licensed Python package. Its performance is illustrated with several examples, and compared to several alternative interpolation schemes.

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arXiv2024

Little Red Dots: an abundant population of faint AGN at z~5 revealed by the EIGER and FRESCO JWST surveys

Characterising the prevalence and properties of faint active galactic nuclei (AGN) in the early Universe is key for understanding the formation of supermassive black holes (SMBHs) and determining their role in cosmic reionization. We perform a spectroscopic search for broad H$α$ emitters at $z\approx4-6$ using deep JWST/NIRCam imaging and wide field slitless spectroscopy from the EIGER and FRESCO surveys. We identify 20 H$α$ lines at $z=4.2-5.5$ that have broad components with line widths from $\sim1200-3700$ km s$^{-1}$, contributing $\sim30-90$ % of the total line flux. We interpret these broad components as being powered by accretion onto SMBHs with implied masses $\sim10^{7-8}$ M$_{\odot}$. In the UV luminosity range M$_{\rm UV}=-21$ to $-18$, we measure number densities of $\approx10^{-5}$ cMpc$^{-3}$. This is an order of magnitude higher than expected from extrapolating quasar UV luminosity functions. Yet, such AGN are found in only $<1$ % of star-forming galaxies at $z\sim5$. The SMBH mass function agrees with large cosmological simulations. In two objects we detect narrow red- and blue-shifted H$α$ absorption indicative, respectively, of dense gas fueling SMBH growth and outflows. We may be witnessing early AGN feedback that will clear dust-free pathways through which more massive blue quasars are seen. We uncover a strong correlation between reddening and the fraction of total galaxy luminosity arising from faint AGN. This implies that early SMBH growth is highly obscured and that faint AGN are only minor contributors to cosmic reionization.

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arXiv2023

Detection of Accretion Shelves Out to the Virial Radius of a Low-Mass Galaxy with JWST

We report the serendipitous discovery of an extended stellar halo surrounding the low-mass galaxy Ark 227 ($M_\ast=5\times10^9 M_\odot$; d=35 Mpc) in deep JWST NIRCam imaging from the Blue Jay Survey. The F200W-F444W color provides robust star-galaxy separation, enabling the identification of stars at very low density. By combining resolved stars at large galactocentric distances with diffuse emission from NIRCam and Dragonfly imaging at smaller distances, we trace the surface brightness and color profiles of this galaxy over the entire extent of its predicted dark matter halo, from 0.1-100 kpc. Controlled N-body simulations have predicted that minor mergers create "accretion shelves" in the surface brightness profile at large radius. We observe such a feature in Ark 227 at 10-20 kpc, which, according to models, could be caused by a merger with total mass ratio 1:10. The metallicity declines over this radial range, further supporting the minor merger scenario. There is tentative evidence of a second shelf at $μ_V\approx 35$ mag arcsec$^{-2}$ extending from 50-100 kpc, along with a corresponding drop in metallicity. The stellar mass in this outermost envelope is $\approx10^7M_\odot$. These results suggest that Ark 227 experienced multiple mergers with a spectrum of lower-mass galaxies -- a scenario that is broadly consistent with the hierarchical growth of structure in a cold dark matter-dominated universe. Finally, we identify an ultra-faint dwarf associated with Ark 227 with $M_\ast\approx10^5 M_\odot$ and $μ_{V,e}=28.1$ mag arcsec$^{-2}$, demonstrating that JWST is capable of detecting very low-mass dwarfs to distances of at least ~30 Mpc.

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arXiv2023

FRESCO: An extended, massive, rapidly rotating galaxy at z=5.3

With the remarkable sensitivity and resolution of JWST in the infrared, measuring rest-optical kinematics of galaxies at $z>5$ has become possible for the first time. This study pilots a new method for measuring galaxy dynamics for highly multiplexed, unbiased samples by combining FRESCO NIRCam grism spectroscopy and JADES medium-band imaging. Here we present one of the first JWST kinematic measurements for a galaxy at $z>5$. We find a significant velocity gradient, which, if interpreted as rotation yields $V_{rot} = 240\pm50$km/s and we hence refer to this galaxy as Twister-z5. With a rest-frame optical effective radius of $r_e=2.25$kpc, the high rotation velocity in this galaxy is not due to a compact size as may be expected in the early universe but rather a high total mass, ${\rm log(M}_{dyn}/{\rm M}_\odot)=11.0\pm0.2$. This is a factor of roughly 4x higher than the stellar mass within the effective radius. We also observe that the radial H$α$ equivalent width profile and the specific star formation rate map from resolved stellar population modeling is centrally depressed by a factor of $\sim1.5$ from the center to $r_e$. Combined with the morphology of the line-emitting gas in comparison to the continuum, this centrally suppressed star formation is consistent with a star-forming disk surrounding a bulge growing inside-out. While large, rapidly rotating disks are common to z~2, the existence of one after only 1Gyr of cosmic time, shown for the first time in ionized gas, adds to the growing evidence that some galaxies matured earlier than expected in the history of the universe.

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arXiv2023

UNCOVER: Illuminating the Early Universe -- JWST/NIRSpec Confirmation of $z > 12$ Galaxies

Observations of high-redshift galaxies provide a critical direct test to the theories of early galaxy formation, yet to date, only three have been spectroscopically confirmed at $z>12$. Due to strong gravitational lensing over a wide area, the galaxy cluster field A2744 is ideal for searching for the earliest galaxies. Here we present JWST/NIRSpec observations of two galaxies: a robust detection at $z_{\rm spec} = 12.393^{+0.004}_{-0.001}$, and a plausible candidate at $z_{\rm spec} = 13.079^{+0.013}_{-0.001}$. The galaxies are discovered in JWST/NIRCam imaging and their distances are inferred with JWST/NIRSpec spectroscopy, all from the JWST Cycle 1 UNCOVER Treasury survey. Detailed stellar population modeling using JWST NIRCam and NIRSpec data corroborates the primeval characteristics of these galaxies: low mass ($\sim 10^8~{\rm M_\odot}$), young, rapidly-assembling, metal-poor, and star-forming. Interestingly, both galaxies are spatially resolved, having lensing-corrected rest-UV effective radii on the order of 300-400 pc, which are notably larger than other spectroscopically confirmed systems at similar redshifts. The observed dynamic range of $z \gtrsim 10$ sizes spans over 1 order of magnitude, implying a significant scatter in the size-mass relation at early times. Deep into the epoch of reionization, these discoveries elucidate the emergence of the first galaxies.

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