20 research outputs found
Massive galaxy formation caught in action at z~5 with JWST
We report the discovery of a compact group of galaxies, CGG-z5, at z~5.2 in
the EGS field covered by the JWST/CEERS survey. CGG-z5 was selected as the
highest overdensity of galaxies at z>2 in recent JWST public surveys and it
consists of six candidate members lying within a projected area of
(1020~kpc). All group members are HST/F435W and
HST/F606W dropouts while securely detected in the JWST/NIRCam bands, yielding a
narrow range of robust photometric redshifts . The most massive
galaxy in the group has a stellar mass log, while
the rest are low-mass satellites (log). While
several group members were already detected in the HST and IRAC bands, the low
stellar masses and the compactness of the structure required the sensitivity
and resolution of JWST for its identification. To assess the nature and
evolutionary path of CGG-z5, we searched for similar compact structures in the
\textsc{Eagle} simulations and followed their evolution with time. We find that
all the identified structures merge into a single galaxy by z=3 and form a
massive galaxy (log) at z~1. This implies that CGG-z5
could be a "proto-massive galaxy" captured during a short-lived phase of
massive galaxy formation.Comment: A&A Letter in pres
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&
COSMOS2020: Identification of High-z Protocluster Candidates in COSMOS
We conduct a systematic search for protocluster candidates at in
the COSMOS field using the recently released COSMOS2020 source catalog. We
select galaxies using a number of selection criteria to obtain a sample of
galaxies that have a high probability of being inside a given redshift bin. We
then apply overdensity analysis to the bins using two density estimators, a
Weighted Adaptive Kernel Estimator and a Weighted Voronoi Tessellation
Estimator. We have found 15 significant () candidate galaxy
overdensities across the redshift range . The majority of the
galaxies appear to be on the galaxy main sequence at their respective epochs.
We use multiple stellar-mass-to-halo-mass conversion methods to obtain a range
of dark matter halo mass estimates for the overdensities in the range of
, at the respective redshifts of the
overdensities. The number and the masses of the halos associated with our
protocluster candidates are consistent with what is expected from the area of a
COSMOS-like survey in a standard CDM cosmology. Through comparison
with simulation, we expect that all the overdensities at will evolve
into a Virgo-/Coma-like clusters at present (i.e., with masses ). Compared to other overdensities identified at
via narrow-band selection techniques, the overdensities presented
appear to have higher stellar masses and star-formation rates.
We compare the evolution in the total star-formation rate and stellar mass
content of the protocluster candidates across the redshift range
and find agreement with the total average star-formation rate from simulations.Comment: 52 pages, 32 figues, 18 tables, main text is 30 pages, appendix is 22
pages, to be published in Ap
COSMOS-Web: Intrinsically Luminous z10 Galaxy Candidates Test Early Stellar Mass Assembly
We report the discovery of 15 exceptionally luminous
candidate galaxies discovered in the first 0.28 deg of JWST/NIRCam imaging
from the COSMOS-Web Survey. These sources span rest-frame UV magnitudes of
, and thus constitute the most intrinsically luminous
candidates identified by JWST to-date. Selected via NIRCam imaging
with Hubble ACS/F814W, deep ground-based observations corroborate their
detection and help significantly constrain their photometric redshifts. We
analyze their spectral energy distributions using multiple open-source codes
and evaluate the probability of low-redshift solutions; we conclude that 12/15
(80%) are likely genuine sources and 3/15 (20%) likely
low-redshift contaminants. Three of our candidates push the limits of
early stellar mass assembly: they have estimated stellar masses
, implying an effective stellar baryon fraction of
, where . The assembly of such stellar reservoirs is made
possible due to rapid, burst-driven star formation on timescales 100\,Myr
where the star-formation rate may far outpace the growth of the underlying dark
matter halos. This is supported by the similar volume densities inferred for
galaxies relative to
-- both about Mpc -- implying they live in halos of comparable
mass. At such high redshifts, the duty cycle for starbursts would be of order
unity, which could cause the observed change in the shape of the UVLF from a
double powerlaw to Schechter at . Spectroscopic redshift
confirmation and ensuing constraints of their masses will be critical to
understanding how, and if, such early massive galaxies push the limits of
galaxy formation in CDM.Comment: 30 pages, 9 figures; ApJ submitte
Sub-millimetre galaxies with Webb:Near-infrared counterparts and multi-wavelength morphology
We utilised the unprecedented depth and resolution of recent early-release science (ERS) JWST observations to define the near-infrared counterparts of sub-millimetre galaxies (SMGs). We identified 45 SCUBA-2 SMG positions within the Cosmic Evolution Early Release Science (CEERS) survey JWST/NIRCam fields. Through an analysis of multi-wavelength p-values, NIRCam colours and predicted SCUBA-2 fluxes, we define 43 JWST/NIRCam counterparts to the SCUBA-2 SMGs, finding a 63 per cent agreement with those identified in prior HST studies. Using EaZy-py, we fitted the available HST and JWST observations to quantify the photometric redshifts of the NIRCam-SMGs, establishing a broad range of redshift from z 0.2-5.4 with a median of z 2.29, in agreement with other studies of SMGs. We identified significant variations in the morphology of the NIRCam-SMGs from isolated discs and spheroidal galaxies to irregular interacting systems. We analysed their rest-frame optical and near-infrared morphological properties (e.g. effective radius (Re), Sérsic index (n), concentration (C), asymmetry (A), clumpiness (S), as well as the Gini and M20 parameters), finding, on average, late-type disc-like morphologies with large scatter into the intermediate and merger regions of the non-parametric parameter space. For the non-merging galaxies, we find a median rest-frame optical size and Sérsic index (and 1Ύ scatter) of Re = 3.10 ± 1.67 kpc and n = 0.96 ± 0.66. Whilst in the rest-frame near-infrared, we establish more compact, higher Sérsic index morphologies (Re = 1.64 ± 0.97, n = 1.85 ± 0.63). We further establish that both the rest-frame optical and near-infrared effective radii correlate negatively (at a 2Ύ level) with redshift, whilst the Sérsic index remains constant with cosmic time. Our results are consistent with the picture of inside-out galaxy evolution, with more centrally concentrated older stellar populations, and more extended, younger star-forming regions whose stellar emission is heavily attenuated in the central regions.</p
Massive galaxy formation caught in action at z ⌠5 with JWST
We report the discovery of a compact group of galaxies, CGG-z5, at zâŒ5.2 in the EGS field covered by the JWST/CEERS survey. CGG-z5 was selected as the highest overdensity of galaxies at z> 2 in recent JWST public surveys and it consists of six candidate members lying within a projected area of 1.5âČĂ 3âČ(10Ă20 kpc2). All group members are HST/F435W and HST/F606W dropouts while securely detected in the JWST/NIRCam bands, yielding a narrow range of robust photometric redshifts 5.0< z< 5.3. The most massive galaxy in the group has a stellar mass log(Mâ/MMidot;)⌠9.8, while the rest are low-mass satellites (log(Mâ/MMidot;)⌠8.4"9.2). While several group members were already detected in the HST and IRAC bands, the low stellar masses and the compactness of the structure required the sensitivity and resolution of JWST for its identification. To assess the nature and evolutionary path of CGG-z5, we searched for similar compact structures in the EAGLE simulations and followed their evolution with time. We find that all the identified structures merge into a single galaxy by z=3 and form a massive galaxy (log(Mâ/MMidot;)> 11) at zâŒ1. This implies that CGG-z5 could be "proto-massive galaxy"captured during a short-lived phase of massive galaxy formation.</p
High-resolution Hubble Space Telescope Imaging Survey of Local Star-forming Galaxies. I. Spatially Resolved Obscured Star Formation with Hα and Paschen-ÎČ Recombination Lines
Tracing the rise of supermassive black holes A panchromatic search for faint, unobscured quasars at z & 6 with COSMOS-Web and other surveys
We report the identification of 64 new candidates of compact galaxies, potentially hosting faint quasars with bolometric luminosities of Lbol = 1043â1046 erg sâ1, residing in the reionization epoch within the redshift range of 6 . z . 8. These candidates were selected by harnessing the rich multiband datasets provided by the emerging JWST-driven extragalactic surveys, focusing on COSMOS-Web, as well as JADES, UNCOVER, CEERS, and PRIMER. Our search strategy includes two stages: applying stringent photometric cuts to catalog-level data and detailed spectral energy distribution fitting. These techniques effectively isolate the quasar candidates while mitigating contamination from low-redshift interlopers, such as brown dwarfs and nearby galaxies. The selected candidates indicate physical traits compatible with low-luminosity active galactic nuclei, likely hosting â105â107 M supermassive black holes (SMBHs) living in galaxies with stellar masses of â108â1010 M . The SMBHs selected in this study, on average, exhibit an elevated mass compared to their hosts, with the mass ratio distribution slightly higher than those of galaxies in the local Universe. As with other high-z studies, this is at least in part due to the selection method for these quasars. An extensive Monte Carlo analysis provides compelling evidence that heavy black hole seeds from the direct collapse scenario appear to be the preferred pathway to mature this specific subset of SMBHs by z â 7. Notably, most of the selected candidates might have emerged from seeds with masses of âŒ105 M , assuming a thin disk accretion with an average Eddington ratio of fEdd = 0.6±0.3 and a radiative efficiency of Δ = 0.2±0.1. This work underscores the significance of further spectroscopic observations, as the quasar candidates presented here offer exceptional opportunities to delve into the nature of the earliest galaxies and SMBHs that formed during cosmic infancy.</p