81 research outputs found
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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 μm 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 indicate Teff = 1300 K and [M/H] ∼ −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 Teff = 550 K, and our analysis indicates the presence of PH3 in the 3–5 μm region, favored over CO2 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
The Differential Assembly History of the Centers and Outskirts of Main Sequence Galaxies at
We present a study of spatially-resolved star formation histories (SFHs) for
60 main-sequence, star-forming galaxies selected from the MOSDEF
spectroscopic survey in the GOODS-N field. Photometry is decomposed into a
central and outer spatial component using observed
colors. The Prospector code is used to
model spectral energy distributions for the centers, outskirts, and integrated
galaxy using HST/ACS and WFC3, Spitzer/IRAC, and ground-based photometry, with
additional constraints on metallicity and spectroscopic redshift from MOSDEF
spectroscopy. For the low-resolution bands, spatially-resolved photometry is
determined with an iterative approach. The reconstructed SFHs indicate that the
majority of galaxies with are observed while their
central regions undergo relatively recent ( Myr) bursts of star
formation, while the outskirts have a smooth, quasi-steady SFH. The enhanced
star formation activity of the central parts is broadly consistent with the
idea that it is produced by highly dissipative gas compaction and accretion.
The broad dispersion of central density and size observed in the sample
suggests that for the selected galaxies this process has started but is still
far from being completed. The implication would be that selecting star-forming
galaxies at cosmic noon frequently includes systems in an "evolved"
evolutionary phase where the centers have recently started a burst of star
formation activity that will likely initiate inside-out quenching in the next
several hundred million years.Comment: 25 pages, 18 figures. Submitted for publication in Ap
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UNCOVER: The Growth of the First Massive Black Holes from JWST/NIRSpec—Spectroscopic Redshift Confirmation of an X-Ray Luminous AGN at z = 10.1
The James Webb Space Telescope is now detecting early black holes (BHs) as they transition from seeds to supermassive BHs. Recently, Bogdan et al. reported the detection of an X-ray luminous supermassive BH, UHZ-1, with a photometric redshift at z \u3e 10. Such an extreme source at this very high redshift provides new insights on seeding and growth models for BHs given the short time available for formation and growth. Harnessing the exquisite sensitivity of JWST/NIRSpec, here we report the spectroscopic confirmation of UHZ-1 at z = 10.073 ± 0.002. We find that the NIRSpec/Prism spectrum is typical of recently discovered z ≈ 10 galaxies, characterized primarily by star formation features. We see no clear evidence of the powerful X-ray source in the rest-frame UV/optical spectrum, which may suggest heavy obscuration of the central BH, in line with the Compton-thick column density measured in the X-rays. We perform a stellar population fit simultaneously to the new NIRSpec spectroscopy and previously available photometry. The fit yields a stellar-mass estimate for the host galaxy that is significantly better constrained than prior photometric estimates (�⋆∼1.4−0.4+0.3×108M⊙). Given the predicted BH mass (MBH ∼ 107–108M⊙), the resulting ratio of MBH/M⋆ remains 2 to 3 orders of magnitude higher than local values, thus lending support to the heavy seeding channel for the formation of supermassive BHs within the first billion years of cosmic evolution
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UNCOVER Spectroscopy Confirms the Surprising Ubiquity of Active Galactic Nuclei in Red Sources at z \u3e 5
The James Webb Space Telescope is revealing a new population of dust-reddened broad-line active galactic nuclei (AGN) at redshifts z ≳ 5. Here we present deep NIRSpec/Prism spectroscopy from the Cycle 1 Treasury program Ultradeep NIRSpec and NIRCam ObserVations before the Epoch of Reionization (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 an 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 Hα with a FWHM \u3e 2000 km s −1, 20% of the current data are inconclusive, and 20% are brown dwarf stars. We propose an updated photometric criterion to select red z \u3e 5 AGN that excludes brown dwarfs and is expected to yield \u3e80% AGN. Remarkably, among all zphot \u3e 5 galaxies with F277W – F444W \u3e 1 in UNCOVER at least 33% are AGN regardless of compactness, climbing to at least 80% AGN for sources with F277W – F444W \u3e 1.6. The confirmed AGN have black hole masses of 107–109M⊙. While their UV luminosities (−16 \u3e MUV \u3e −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 107–109M⊙ black holes radiating at ∼10%–40% the Eddington limit. The number densities are surprisingly high at ∼10−5 Mpc−3 mag−1, 100 times more common than the faintest UV-selected quasars, while accounting for ∼1% of the UV-selected galaxies. While their UV faintness suggests they may not contribute strongly to reionization, their ubiquity poses challenges to models of black hole growth
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UNCOVER: Illuminating the Early Universe—JWST/NIRSpec Confirmation of z \u3e 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 \u3e 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 zspec 12.393 0.001 0.004 = - + , and a plausible candidate at zspec 13.079 0.001 0.013 = - + . 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 (∼108 Me), 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 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
Rapid Quenching of Galaxies at Cosmic Noon
The existence of massive quiescent galaxies at high redshift seems to require
rapid quenching, but it is unclear whether all quiescent galaxies have gone
through this phase and what physical mechanisms are involved. To study rapid
quenching, we use rest-frame colors to select 12 young quiescent galaxies at . From spectral energy distribution fitting, we find that they all
experienced intense starbursts prior to rapid quenching. We confirm this with
deep Magellan/FIRE spectroscopic observations for a subset of seven galaxies.
Broad emission lines are detected for two galaxies and are most likely caused
by AGN activity. The other five galaxies do not show any emission features,
suggesting that gas has already been removed or depleted. Most of the rapidly
quenched galaxies are more compact than normal quiescent galaxies, providing
evidence for a central starburst in the recent past. We estimate an average
transition time of for the rapid quenching phase. Approximately
of quiescent galaxies at have gone through rapid quenching; this
fraction increases to at . We identify analogs in the TNG100
simulation and find that rapid quenching for these galaxies is driven by AGN,
and for half of the cases, gas-rich major mergers seem to trigger the
starburst. We conclude that these massive quiescent galaxies are not just
rapidly quenched but also rapidly formed through a major starburst. We
speculate that mergers drive gas inflow towards the central regions and grow
supermassive black holes, leading to rapid quenching by AGN feedback.Comment: Submitted to ApJ. Comments are welcom
Remarkably Compact Quiescent Candidates at in JWST-CEERS
In this letter, we measure the rest-frame optical and near-infrared sizes of
ten quiescent candidates at , first reported by Carnall et al. (2023a).
We use James Webb Space Telescope (JWST) Near-Infrared Camera (NIRCam) F277W
and F444W imaging obtained through the public CEERS Early Release Science (ERS)
program and imcascade, an astronomical fitting code that utilizes
Multi-Gaussian Expansion, to carry out our size measurements. When compared to
the extrapolation of rest-optical size-mass relations for quiescent galaxies at
lower redshift, eight out of ten candidates in our sample (80%) are on average
more compact by 40%. Seven out of ten candidates (70%) exhibit rest-frame
infrared sizes 10% smaller than rest-frame optical sizes, indicative of
negative color gradients. Two candidates (20%) have rest-frame infrared sizes
1.4 larger than rest-frame optical sizes; one of these candidates
exhibits signs of ongoing or residual star formation, suggesting this galaxy
may not be fully quenched. The remaining candidate is unresolved in both
filters, which may indicate an Active Galactic Nuclei (AGN). Strikingly, we
observe three of the most massive galaxies in the sample
(log(M/M) = 10.74 - 10.95) are extremely compact, with
effective radii 0.7 kpc. Our findings provide no indication that the
size evolution relation flattens out, and may indicate that the size evolution
of quiescent galaxies is steeper than previously anticipated beyond .Comment: Accepted for publication in ApJL. 11 pages, 4 figures, 1 tabl
Dust attenuation, dust content and geometry of star-forming galaxies
We analyse the joint distribution of dust attenuation and projected axis
ratios, together with galaxy size and surface brightness profile information,
to infer lessons on the dust content and star/dust geometry within star-forming
galaxies at 0 < z <2.5. To do so, we make use of large observational datasets
from KiDS+VIKING+HSC-SSP and extend the analysis out to redshift z = 2.5 using
the HST surveys CANDELS and 3D-DASH. We construct suites of SKIRT radiative
transfer models for idealized galaxies observed under random viewing angles
with the aim of reproducing the aforementioned distributions, including the
level and inclination dependence of dust attenuation. We find that
attenuation-based dust mass estimates are at odds with constraints from
far-infrared observations, especially at higher redshifts, when assuming smooth
star and dust geometries of equal extent. We demonstrate that UV-to-near-IR and
far-infrared constraints can be reconciled by invoking clumpier dust geometries
for galaxies at higher redshifts and/or very compact dust cores. We discuss
implications for the significant wavelength- and redshift-dependent differences
between half-light and half-mass radii that result from spatially varying dust
columns within -- especially massive -- star-forming galaxies.Comment: Accepted for publication in MNRA
Quantifying the Effects of Known Unknowns on Inferred High-redshift Galaxy Properties: Burstiness, the IMF, and Nebular Physics
The era of the James Webb Space Telescope ushers stellar populations models
into uncharted territories, particularly at the high-redshift frontier. In a
companion paper, we apply the \texttt{Prospector} Bayesian framework to jointly
infer galaxy redshifts and stellar populations properties from broad-band
photometry as part of the UNCOVER survey. Here we present a comprehensive error
budget in spectral energy distribution (SED) modeling. Using a
sample, we quantify the systematic shifts stemming from various model choices
in inferred stellar mass, star formation rate (SFR), and age. These choices
encompass different timescales for changes in the star formation history (SFH),
non-universal stellar initial mass functions (IMF), and the inclusion of
variable nebular abundances, gas density and ionizing photon budget. We find
that the IMF exerts the strongest influence on the inferred properties: the
systematic uncertainties can be as much as 1 dex, 2--5 times larger than the
formal reported uncertainties in mass and SFR; and importantly, exceed the
scatter seen when using different SED fitting codes. This means that a common
practice in the literature of assessing uncertainties in SED-fitting processes
by comparing multiple codes is substantively underestimating the true
systematic uncertainty. Highly stochastic SFHs change the inferred SFH by much
larger than the formal uncertainties, and introduce dex systematics
in SFR and dex systematics in average age. Finally, employing a
flexible nebular emission model causes dex systematic increase in
mass, comparable to the formal uncertainty. This paper constitutes one of the
initial steps toward a complete uncertainty estimate in SED modeling.Comment: Submitted to ApJ. 18 pages, 8 figures, 2 table
The Heavy Metal Survey: Star Formation Constraints and Dynamical Masses of 21 Massive Quiescent Galaxies at z~1.4-2.2
In this paper, we present the Heavy Metal Survey, which obtained ultra-deep
medium-resolution spectra of 21 massive quiescent galaxies at with Keck/LRIS and MOSFIRE. With integration times of up to 16
hrs per band per galaxy, we observe numerous Balmer and metal absorption lines
in atmospheric windows. We successfully derive spectroscopic redshifts for all
21 galaxies and for 19 we also measure stellar velocity dispersions
(), ages, and elemental abundances, as detailed in an accompanying
paper. Except for one emission-line AGN, all galaxies are confirmed as
quiescent through their faint or absent H emission and evolved stellar
spectra. For most galaxies exhibiting faint H, elevated [NII]/H
suggests a non-star-forming origin. We calculate dynamical masses () by combining with structural parameters obtained from
HST/COSMOS(-DASH), and compare them with stellar masses () derived using
spectrophotometric modeling, considering various assumptions. For a fixed
initial mass function (IMF), we observe a strong correlation between and . This correlation may suggest that a varying IMF, with
high- galaxies being more bottom-heavy, was already in place at
. When implementing the -dependent IMF found in the cores of
nearby early-type galaxies and correcting for biases in our stellar mass and
size measurements, we find a low scatter in of 0.14 dex.
However, these assumptions result in unphysical stellar masses, which exceed
the dynamical masses by 34%. This tension suggests that distant quiescent
galaxies do not simply grow inside-out into today's massive early-type galaxies
and the evolution is more complicated.Comment: Submitted to ApJ (25 pages, 11 figures
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