121 research outputs found
Uncovering the MIR emission of quiescent galaxies with
We present a study of the mid-IR (MIR) emission of quiescent galaxies (QGs)
beyond the local universe. Using deep imaging in the SMACS-0723 cluster
field we identify a mass limited (M) sample of
intermediate redshift QGs () and perform modeling of their
rest-frame UV to MIR photometry. We find that QGs exhibit a range of MIR
spectra that are composed of a stellar continuum and a dust component that is
1-2 orders of magnitude fainter to that of star-forming galaxies. The observed
scatter in the MIR spectra, especially at m, can be
attributed to different dust continuum levels and/or the presence of Polycyclic
Aromatic Hydrocarbons (PAHs) features. The latter would indicate enhanced 11.3-
and 12.7 m PAHs strengths with respect to those at 6.2- and 7.7m,
consistent with the observed spectra of local ellipticals and indicative of
soft radiation fields. Finally, we augment the average UV-to-MIR spectrum of
the population with cold dust and gas emission in the far-IR/mm and construct a
panchromatic UV-to-radio SED that can serve as a template for the future
exploration of the interstellar medium of QGs with ALMA and .Comment: The panchromatic QG SED has been made publicly available at
http://www.georgiosmagdis.com/softwar
Unveiling the hidden universe with JWST: The contribution of dust-obscured galaxies to the stellar mass function at
The emergence of massive, optically-faint galaxies in infrared observations
has revealed that our view of the high-redshift Universe was previously
incomplete. With the advent of JWST, we can for the first time probe the
rest-frame optical emission of galaxies at with high sensitivity and
spatial resolution, thus moving towards a more complete census of the galaxy
population at high redshifts. To this end, we present a sample of 148 massive,
dusty galaxies from the JWST/CEERS survey, colour-selected using solely JWST
bands. With deep JWST/NIRCam data from 1.15m to 4.44m and ancillary
HST/ACS and WFC3 data, we determine the physical properties of our sample using
spectral energy distribution fitting with BAGPIPES. We demonstrate that our
selection method efficiently identifies massive () and dusty () sources, with a majority at and predominantly lying on the
galaxy main-sequence. The main results of this work are the stellar mass
functions (SMF) of red, optically-faint galaxies from redshifts between
: these galaxies make up a significant fraction of the pre-JWST total
SMF at , and dominate the high-mass end of the pre-JWST SMF at
and , suggesting that our census of the galaxy population needs
amendment at these epochs. While larger areas need to be surveyed in the
future, our results suggest already that the integrated stellar mass density at
may have been underestimated by
20-25% at , and 110% at .Comment: 19 pages, 10 figures, submitted to MNRA
HSC-CLAUDS survey: The star formation rate functions since z ~ 2 and comparison with hydrodynamical simulations
Star formation rate functions (SFRFs) give an instantaneous view of the
distribution of star formation rates (SFRs) in galaxies at different epochs.
They are a complementary and more stringent test for models than the galaxy
stellar mass function, which gives an integrated view of the past star
formation activity. However, the exploration of SFRFs has been limited thus far
due to difficulties in assessing the SFR from observed quantities and probing
the SFRF over a wide range of SFRs. We overcome these limitations thanks to an
original method that predicts the infrared luminosity from the rest-frame
UV/optical color of a galaxy and then its SFR over a wide range of stellar
masses and redshifts. We applied this technique to the deep imaging survey
HSC-CLAUDS combined with near-infrared and UV photometry. We provide the first
SFR functions with reliable measurements in the high- and low-SFR regimes up to
and compare our results with previous observations and four
state-of-the-art hydrodynamical simulations.Comment: 29 pages, 19 figure
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: 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
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
JWST and ALMA discern the assembly of structural and obscured components in a high-redshift starburst galaxy
We present observations and analysis of the starburst, PACS-819, at z=1.45
( M), using high-resolution (;
0.8 kpc) ALMA and multi-wavelength JWST images from the COSMOS-Web program.
Dissimilar to HST/ACS images in the rest-frame UV, the redder NIRCam and MIRI
images reveal a smooth central mass concentration and spiral-like features,
atypical for such an intense starburst. Through dynamical modeling of the CO
J=5--4 emission with ALMA, PACS-819 is rotation-dominated thus has a disk-like
nature. However, kinematic anomalies in CO and asymmetric features in the bluer
JWST bands (e.g., F150W) support a more disturbed nature likely due to
interactions. The JWST imaging further enables us to map the distribution of
stellar mass and dust attenuation, thus clarifying the relationships between
different structural components, not discernable in the previous HST images.
The CO J = 5 -- 4 and FIR dust continuum emission are co-spatial with a
heavily-obscured starbursting core (<1 kpc) which is partially surrounded by
much less obscured star-forming structures including a prominent arc, possibly
a tidally-distorted dwarf galaxy, and a clump, either a sign of an ongoing
violent disk instability or a recently accreted low-mass satellite. With
spatially-resolved maps, we find a high molecular gas fraction in the central
area reaching (/) and short depletion times
( 120 Myrs) across the entire system. These
observations provide insights into the complex nature of starbursts in the
distant universe and underscore the wealth of complementary information from
high-resolution observations with both ALMA and JWST.Comment: 18 pages, 12 figures, Submitted to Ap
The COSMOS-Web ring: in-depth characterization of an Einstein ring lensing system at z~2
Aims. We provide an in-depth analysis of the COSMOS-Web ring, an Einstein
ring at z=2 that we serendipitously discovered in the COSMOS-Web survey and
possibly the most distant lens discovered to date.
Methods. We extract the visible and NIR photometry from more than 25 bands
and we derive the photometric redshifts and physical properties of both the
lens and the source with three different SED fitting codes. Using JWST/NIRCam
images, we also produce two lens models to (i) recover the total mass of the
lens, (ii) derive the magnification of the system, (iii) reconstruct the
morphology of the lensed source, and (iv) measure the slope of the total mass
density profile of the lens.
Results. The lens is a very massive and quiescent (sSFR < 10^(-13) yr-1)
elliptical galaxy at z = 2.02 \pm 0.02 with a total mass Mtot(<thetaE) = (3.66
\pm 0.36) x 10^11 Msun and a stellar mass M* = (1.37 \pm 0.14) x 10^11 Msun.
Compared to SHMRs from the literature, we find that the total mass is
consistent with the presence of a DM halo of mass Mh = 1.09^(+1.46)_(-0.57) x
10^13 Msun. In addition, the background source is a M* = (1.26 \pm 0.17) x
10^10 Msun star-forming galaxy (SFR=(78 \pm 15) Msun/yr) at z = 5.48 \pm 0.06.
Its reconstructed morphology shows two components with different colors. Dust
attenuation values from SED fitting and nearby detections in the FIR also
suggest it could be partially dust-obscured.
Conclusions. We find the lens at z=2. Its total, stellar, and DM halo masses
are consistent within the Einstein ring, so we do not need any unexpected
changes in our description of the lens (e.g. change its IMF or include a
non-negligible gas contribution). The most likely solution for the lensed
source is at z = 5.5. Its reconstructed morphology is complex and highly
wavelength dependent, possibly because it is a merger or a main sequence galaxy
with a heterogeneous dust distribution.Comment: 16 pages, submitted to A&
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