13 research outputs found
The archival discovery of a strong Lyman- and [CII] emitter at z = 7.677
We report the archival discovery of Lyman- emission from the bright
ultraviolet galaxy Y002 at , spectroscopically confirmed by its
ionized carbon [CII] 158m emission line. The Ly line is spatially
associated with the rest-frame UV stellar emission (~-22, 2x
brighter than ) and it appears offset from the peak of the
extended [CII] emission at the current ~1" spatial resolution. We derive an
estimate of the unobscured SFR(UV)= yr and set an
upper limit of SFR(IR) yr from the far-infrared wavelength
range, which globally place Y002 on the SFR(UV+IR)-L([CII]) correlation
observed at lower redshifts. In terms of velocity, the peak of the Ly
emission is redshifted by (Ly)~500 km s from the
systemic redshift set by [CII] and a high-velocity tail extends to up to ~1000
km s. The velocity offset is up to ~3.5x higher than the average
estimate for similarly UV-bright emitters at z~6-7, which might suggest that we
are witnessing the merging of two clumps. A combination of strong outflows and
the possible presence of an extended ionized bubble surrounding Y002 would
likely facilitate the escape of copious Ly light, as indicated by the
large equivalent width EW(Ly)= \r{A}. Assuming that [CII]
traces the neutral hydrogen, we estimate a HI gas fraction of for Y002 as a system and speculate that patches of high
HI column densities could contribute to explain the observed spatial offsets
between Ly and [CII] emitting regions. The low dust content, implied by
the non-detection of the far-infrared continuum emission at rest-frame ~160
m, would be sufficient to absorb any potential Ly photons produced
within the [CII] clump as a result of large HI column densities.Comment: 10 pages, 4 figures. Accepted for publication in The Astrophysical
Journal Letter
A massive quiescent galaxy in a group environment at
We report on the spectroscopic confirmation of a massive quiescent galaxy at
in the COSMOS field with Keck/MOSFIRE. The object was
first identified as a galaxy with suppressed star formation at
from the COSMOS2020 catalog. The follow-up
spectroscopy with MOSFIRE in the -band reveals a faint [OII] emission and
the Balmer break, indicative of evolved stellar populations. We perform the
spectral energy distribution fitting using both the photometry and spectrum to
infer physical properties. The obtained stellar mass is high () and the current star formation rate is more than 1 dex
below that of main-sequence galaxies at . Its star formation history
suggests that this galaxy experienced starburst at followed by a rapid
quenching phase. This is one of the youngest quiescent galaxies at and is
likely a galaxy in the process of being quenched. An unique aspect of the
galaxy is that it is in an extremely dense region; there are four massive
star-forming galaxies at located within 150 physical
kpc from the galaxy. Interestingly, three of them have strongly overlapping
virial radii with that of the central quiescent galaxy (), suggesting that the over-density region is likely the
highest redshift candidate of a dense group with a spectroscopically confirmed
quiescent galaxy at the center. The group provides us with an unique
opportunity to gain insights into the role of the group environment for
quenching at 4 - 5 corresponding to the formation epoch of massive
elliptical galaxies in the local Universe.Comment: 13 pages, 7 figures, 2 tables; submitted to Ap
COSMOS2020: Discovery of a protocluster of massive quiescent galaxies at
Protoclusters of galaxies have been found in the last quarter century.
However, most of them have been found through the overdensity of star-forming
galaxies, and there had been no known structures identified by multiple
spectroscopically confirmed quiescent galaxies at . In this letter, we
report the discovery of an overdense structure of massive quiescent galaxies
with the spectroscopic redshift in the COSMOS field, QO-1000. We first
photometrically identify this structure as a overdensity with 14
quiescent galaxies in from the COSMOS2020 catalog. We
then securely confirm the spectroscopic redshifts of 4 quiescent galaxies by
detecting multiple Balmer absorption lines with Keck/MOSFIRE. All the
spectroscopically confirmed members are massive
() and located in a narrow redshift range
(). Moreover, three of them are in the in
the transverse direction at the same redshift (). Such a
concentration of four spectroscopically confirmed quiescent galaxies implies
that QO-1000 is times denser than in the general field. In addition, we
confirm that they form a red sequence in the color. This structure's
halo mass is estimated as from their
stellar mass. Similar structures found in the IllustrisTNG simulation are
expected to evolve into massive galaxy clusters with at . These results suggest that QO-1000 is a more
mature protocluster than the other known protoclusters. It is likely in a
transition phase between the star-forming protoclusters and the quenched galaxy
clusters.Comment: 11 pages, 4 figures, 1 table, accepted for publication in ApJ
A First Look at Spatially Resolved Balmer Decrements at from JWST NIRISS Slitless Spectroscopy
We present the first results on the spatial distribution of dust attenuation
at traced by the Balmer Decrement, H/H, in
emission-line galaxies using deep JWST NIRISS slitless spectroscopy from the
CAnadian NIRISS Unbiased Cluster Survey (CANUCS). H and H
emission line maps of emission-line galaxies are extracted and stacked in bins
of stellar mass for two grism redshift bins, and
. Surface brightness profiles for the Balmer Decrement are
measured and radial profiles of the dust attenuation towards H,
, are derived. In both redshift bins, the integrated
Balmer Decrement increases with stellar mass. Lower mass
(Log(/M)) galaxies have centrally
concentrated, negative dust attenuation profiles whereas higher mass galaxies
(Log(/M)) have flat dust attenuation
profiles. The total dust obscuration is mild, with on average and
mag in the low and high redshift bins respectively. We model the
typical light profiles of star-forming galaxies at these redshifts and stellar
masses with GALFIT and apply both uniform and radially varying dust attenuation
corrections based on our integrated Balmer Decrements and radial dust
attenuation profiles. If these galaxies were observed with typical JWST NIRSpec
slit spectroscopy ( shutters), on average,
H star formation rates (SFRs) measured after slit-loss corrections
assuming uniform dust attenuation will overestimate the total SFR by and at and
respectively.Comment: 7 pages, 5 figures, submitted to ApJ
COSMOS2020: Exploring the dawn of quenching for massive galaxies at 3 < z < 5 with a new colour selection method
We select and characterise a sample of massive
(log(MM) quiescent galaxies (QGs) at in the
latest COSMOS2020 catalogue. QGs are selected using a new rest-frame colour
selection method, based on their probability of belonging to the quiescent
group defined by a Gaussian Mixture Model (GMM) trained on rest-frame colours
() of similarly massive galaxies at . We calculate the
quiescent probability threshold above which a galaxy is classified as quiescent
using simulated galaxies from the SHARK semi-analytical model. We find that at
in SHARK, the GMM/ method out-performs classical rest-frame
selection and is a viable alternative. We select galaxies as quiescent
based on their probability in COSMOS2020 at , and compare the selected
sample to both and selected samples. We find that although the
new selection matches and in number, the overlap between colour
selections is only , implying that rest-frame colour commonly used
at lower redshifts selections cannot be equivalently used at . We compute
median rest-frame SEDs for our sample and find the median quiescent galaxy at
has a strong Balmer/4000 Angstrom break, and residual flux
indicating recent quenching. We find the number densities of the entire
quiescent population (including post-starbursts) more than doubles from
Mpc at to
Mpc at , confirming that the onset of massive galaxy quenching
occurs as early as .Comment: 19 pages, 10 figures + appendix. Accepted for publication in AJ. Both
the GMM model and code to calculate quiescent probabilities from rest frame
flux densities are made available online at
https://github.com/kmlgould/GMM-quiescen
Cosmic Vine: A z=3.44 Large-Scale Structure Hosting Massive Quiescent Galaxies
We report the discovery of a large-scale structure at z=3.44 revealed by JWST
data in the EGS field. This structure, dubbed "Cosmic Vine", consists of 20
galaxies with spectroscopic redshifts at and six galaxy
overdensities with consistent photometric redshifts, making up a vine-like
structure extending over a ~4x0.2 pMpc^2 area. The two most massive galaxies
(M*~10^10.9 Msun) of the Cosmic Vine are found to be quiescent with
bulge-dominated morphologies (). Comparisons with simulations suggest
that the Cosmic Vine would form a cluster with halo mass >10^14 Msun at z=0,
and the two massive galaxies are likely forming the brightest cluster galaxies
(BCGs). The results unambiguously reveal that massive quiescent galaxies can
form in growing large-scale structures at z>3, thus disfavoring the
environmental quenching mechanisms that require a virialized cluster core.
Instead, as suggested by the interacting and bulge-dominated morphologies, the
two galaxies are likely quenched by merger-triggered starburst or AGN feedback
before falling into a cluster core. Moreover, we found that the observed
specific star formation rates of massive quiescent galaxies in z>3 dense
environments are two orders of magnitude lower than that of the BCGs in the
TNG300 simulation. This discrepancy potentially poses a challenge to the models
of massive cluster galaxy formation. Future studies comparing a large sample
with dedicated cluster simulations are required to solve the problem.Comment: Submitted to A&
Size - Stellar Mass Relation and Morphology of Quiescent Galaxies at in Public Fields
We present the results of a systematic study of the rest-frame optical
morphology of quiescent galaxies at using the Near-Infrared Camera
(NIRCam) onboard . Based on a sample selected by color or
color, we focus on 26 quiescent galaxies with
at with publicly
available data. Their sizes are constrained by fitting the S\'ersic
profile to all available NIRCam images. We see a negative correlation between
the observed wavelength and the size in our sample and derive their size at the
rest-frame taking into account this trend. Our quiescent
galaxies show a significant correlation between the rest-frame size and the stellar mass at . The analytical fit for them at
implies that our size - stellar mass relations
are below those at lower redshifts, with the amplitude of
at . This value agrees with the
extrapolation from the size evolution of quiescent galaxies at in the
literature, implying that the size of quiescent galaxies increases
monotonically from . Our sample is mainly composed of galaxies with
bulge-like structures according to their median S\'ersic index and axis ratio
of and , respectively. On the other hand, there is a
trend of increasing fraction of galaxies with low S\'ersic index, suggesting
might be the epoch of onset of morphological transformation with a
fraction of very notable disky quenched galaxies.Comment: 23 pages, 16 figures, 2 tables; submitted to Ap
Efficient NIRCam Selection of Quiescent Galaxies at 3 < z < 6 in CEERS
© 2024 The Author(s). Published by the American Astronomical Society. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/Substantial populations of massive quiescent galaxies at z â„ 3 challenge our understanding of rapid galaxy growth and quenching over short timescales. In order to piece together this evolutionary puzzle, more statistical samples of these objects are required. Established techniques for identifying massive quiescent galaxies are increasingly inefficient and unconstrained at z > 3. As a result, studies report that as much as 70% of quiescent galaxies at z > 3 may be missed from existing surveys. In this work, we propose a new empirical color selection technique designed to select massive quiescent galaxies at 3 âČ z âČ 6 using JWST NIRCam imaging data. We use empirically constrained galaxy spectral energy distribution (SED) templates to define a region in the F277W â F444W versus F150W â F277W color plane that captures quiescent galaxies at z > 3. We apply these color selection criteria to the Cosmic Evolution Early Release Science (CEERS) Survey and use SED fitting on sources in the region to identify 44 candidate z âł 3 quiescent galaxies. Over half of these sources are newly discovered and, on average, exhibit specific star formation rates of poststarburst galaxies. Most of these sources would not be discovered using canonical UVJ diagrams. We derive volume density estimates of n ⌠1â4 Ă 10â5 Mpcâ3 at 3 < z < 5, finding excellent agreement with existing reports on similar populations in the CEERS field. Thanks to NIRCamâs wavelength coverage and sensitivity, this technique provides an efficient tool to search for large samples of these rare galaxies.Peer reviewe
A First Look at Spatially Resolved Balmer Decrements at 1.0 < z < 2.4 from JWST NIRISS Slitless Spectroscopy
We present the first results on the spatial distribution of dust attenuation at 1.0 < z < 2.4 traced by the Balmer decrement, H α /H ÎČ , in emission-line galaxies using deep JWST NIRISS slitless spectroscopy from the CAnadian NIRISS Unbiased Cluster Survey (CANUCS). H α  and H ÎČ Â emission-line maps of emission-line galaxies are extracted and stacked in bins of stellar mass for two grism redshift bins, 1.0 < z _grism < 1.7 and 1.7 < z _grism < 2.4. Surface brightness profiles for the Balmer decrement are measured and radial profiles of the dust attenuation toward  H α , A _H _α , are derived. In both redshift bins, the integrated Balmer decrement increases with stellar mass. Lower-mass (7.6 †Log( M _* / M _â ) < 10.0) galaxies have centrally concentrated, negative dust attenuation profiles whereas higher-mass galaxies (10.0 †Log( M _* / M _â ) < 11.1) have flat dust attenuation profiles. The total dust obscuration is mild, with on average 0.07 ± 0.07 and 0.14 ± 0.07 mag in the low- and high-redshift bins respectively. We model the typical light profiles of star-forming galaxies at these redshifts and stellar masses with GALFIT and apply both uniform and radially varying dust attenuation corrections based on our integrated Balmer decrements and radial dust attenuation profiles. If the H α  star formation rates (SFRs) of these galaxies were measured after slit-loss corrections assuming uniform dust attenuation with typical JWST NIRSpec slit spectroscopy (0.âł2 Ă 0.âł5 shutters), the total SFR will be overestimated by 6% ± 21% and 26% ± 9% at 1.0 †z < 1.7 and 1.7 †z < 2.4 respectively
An Atlas of Color-selected Quiescent Galaxies at z > 3 in Public JWST Fields
We present the results of a systematic search for candidate quiescent galaxies in the distant universe in 11 JWST fields with publicly available observations collected during the first 3 months of operations and covering an effective sky area of âŒ145 arcmin ^2 . We homogeneously reduce the new JWST data and combine them with existing observations from the Hubble Space Telescope. We select a robust sample of âŒ80 candidate quiescent and quenching galaxies at 3 3, as could be expected for highly clustered massive systems. Importantly, JWST enables the robust identification of quenching/quiescent galaxy candidates at lower masses and higher redshifts than before, challenging standard formation scenarios. All data products, including the literature compilation, are made publicly available