We present 16 new ultrabright HAB 25 galaxy candidates at z ∼ 8 identified over the COSMOS/UltraVISTA field. The new search takes advantage of the deepest-available ground-based optical and ...near-infrared observations, including the DR3 release of UltraVISTA and full-depth Spitzer/IRAC observations from the SMUVS and SPLASH programs. Candidates are selected using Lyman-break color criteria, combined with strict optical non-detection and SED-fitting criteria, designed to minimize contamination by low-redshift galaxies and low-mass stars. HST/WFC3 coverage from the DASH program reveals that one source evident in our ground-based near-IR data has significant substructure and may actually correspond to 3 separate z ∼ 8 objects, resulting in a total sample of 18 galaxies, 10 of which seem to be fairly robust (with a >97% probability of being at z > 7). The UV-continuum slope β for the bright z ∼ 8 sample is β = −2.2 0.6, bluer but still consistent with that of similarly bright galaxies at z ∼ 6 (β = −1.55 0.17) and z ∼ 7 (β = −1.75 0.18). Their typical stellar masses are M , with the SFRs of yr−1, specific SFR of Gyr−1, stellar ages of Myr, and low dust content mag. Using this sample we constrain the bright end of the z ∼ 8 UV luminosity function. When combined with recent empty field luminosity function estimates at similar redshifts, the resulting z ∼ 8 luminosity function can be equally well represented by either a Schechter or a double-power-law form. Assuming a Schechter parameterization, the best-fit characteristic magnitude is mag with a very steep faint-end slope . These new candidates include some of the brightest objects found at these redshifts, 0.5-1.0 magnitude brighter than those found over CANDELS, and providing excellent targets for spectroscopic and longer-wavelength follow-up studies.
Abstract
We select and characterize a sample of massive (log(
M
*
/
M
⊙
) > 10.6) quiescent galaxies (QGs) at 3 <
z
< 5 in the latest Cosmological Evolution Survey catalog (COSMOS2020). QGs are ...selected using a new rest-frame color-selection method, based on their probability of belonging to the quiescent group defined by a Gaussian mixture model (GMM) trained on rest-frame colors (
NUV
−
U
,
U
−
V
,
V
−
J
) of similarly massive galaxies at 2 <
z
< 3. 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
z
≥ 3 in
shark
, the GMM/
NUVU
−
VJ
method outperforms classical rest-frame
UVJ
selection and is a viable alternative. We select galaxies as quiescent based on their probability in COSMOS2020 at 3 <
z
< 5, and compare the selected sample to both
UVJ
- and
NUVrJ
-selected samples. We find that, although the new selection matches
UVJ
and
NUVrJ
in number, the overlap between color selections is only ∼50%–80%, implying that rest-frame color commonly used at lower-redshift selections cannot be equivalently used at
z
> 3. We compute median rest-frame spectral energy distributions for our sample and find the median QG at 3 <
z
< 5 has a strong Balmer/4000 Å break, and residual
NUV
flux indicating recent quenching. We find the number densities of the entire quiescent population (including post-starbursts) more than doubles from 3.5 ± 2.2 × 10
−6
Mpc
−3
at 4 <
z
< 5 to 1.4 ± 0.4 × 10
−5
Mpc
−3
at 3 <
z
< 4, confirming that the onset of massive galaxy quenching occurs as early as 3 <
z
< 5.
We report on the discovery of three especially bright candidate galaxies. Five sources were targeted for follow-up with the Hubble Space Telescope (HST)/Wide Field Camera 3 (WFC3), selected from a ...larger sample of 16 bright ( mag) candidate Lyman break galaxies (LBGs) identified over 1.6 degrees2 of the COSMOS/UltraVISTA field. These were selected as Y and J dropouts by leveraging the deep (Y-to- mag, ) NIR data from the UltraVISTA DR3 release, deep ground-based optical imaging from the CFHTLS and Suprime-Cam programs, and Spitzer/IRAC mosaics combining observations from the SMUVS and SPLASH programs. Through the refined spectral energy distributions, which now also include new HyperSuprimeCam g-, r-, i-, z-, and Y-band data, we confirm that 3/5 galaxies have robust , consistent with the initial selection. The remaining 2/5 galaxies have a nominal . However, with HST data alone, these objects have increased probability of being at . We measure mean UV continuum slopes for the three galaxies, marginally bluer than similarly luminous in CANDELS but consistent with previous measurements of similarly luminous galaxies at . The circularized effective radius for our brightest source is 0.9 0.3 kpc, similar to previous measurements for a bright galaxy and bright galaxies. Finally, enlarging our sample to include the six brightest LBGs identified over UltraVISTA (i.e., including three other sources from Labbé et al.) we estimate for the first time the volume density of galaxies at the extreme bright end ( mag) of the UV luminosity function. Despite this exceptional result, the still large statistical uncertainties do not allow us to discriminate between a Schechter and a double-power-law form.
Cosmic Evolution of Gas and Star Formation Scoville, Nick; Faisst, Andreas; Weaver, John ...
The Astrophysical journal,
02/2023, Letnik:
943, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract
Atacama Large Millimeter/submillimeter Array (ALMA) observations of the long-wavelength dust continuum are used to estimate the gas masses in a sample of 708 star-forming galaxies at
z
= ...0.3−4.5. We determine the dependence of gas masses and star formation efficiencies (SFEs; SFR per unit gas mass) on redshift (z),
M
*
, and star formation rate (SFR) relative to the main sequence (MS). We find that 70% of the increase in SFRs of the MS is due to the increased gas masses at earlier epochs, while 30% is due to increased efficiency of star formation (SF). For galaxies above the MS this is reversed—with 70% of the increased SFR relative to the MS being due to elevated SFEs. Thus, the major evolution of star formation activity at early epochs is driven by increased gas masses, while the starburst activity taking galaxies above the MS is due to enhanced triggering of star formation (likely due to galactic merging). The interstellar gas peaks at
z
= 2 and dominates the stellar mass down to
z
= 1.2. Accretion rates needed to maintain continuity of the MS evolution reach >100
M
⊙
yr
−1
at
z
> 2. The galactic gas contents are likely the driving determinant for both the rise in SF and AGN activity from
z
= 5 to their peak at
z
= 2 and subsequent fall at lower
z
. We suggest that for self-gravitating clouds with supersonic turbulence, cloud collisions and the filamentary structure of the clouds regulate the star formation activity.
Abstract
We present a new method based on information theory to find the optimal number of bands required to measure the physical properties of galaxies with desired accuracy. As a proof of concept, ...using the recently updated COSMOS catalog (COSMOS2020), we identify the most relevant wave bands for measuring the physical properties of galaxies in a Hawaii Two-0- (H20) and UVISTA-like survey for a sample of
i
< 25 AB mag galaxies. We find that with the available
i
-band fluxes,
r
,
u
, IRAC/
ch
2, and
z
bands provide most of the information regarding the redshift with importance decreasing from
r
band to
z
band. We also find that for the same sample, IRAC/
ch
2,
Y
,
r
, and
u
bands are the most relevant bands in stellar-mass measurements with decreasing order of importance. Investigating the intercorrelation between the bands, we train a model to predict UVISTA observations in near-IR from H20-like observations. We find that magnitudes in the
YJH
bands can be simulated/predicted with an accuracy of 1
σ
mag scatter ≲0.2 for galaxies brighter than 24 AB mag in near-IR bands. One should note that these conclusions depend on the selection criteria of the sample. For any new sample of galaxies with a different selection, these results should be remeasured. Our results suggest that in the presence of a limited number of bands, a machine-learning model trained over the population of observed galaxies with extensive spectral coverage outperforms template fitting. Such a machine-learning model maximally comprises the information acquired over available extensive surveys and breaks degeneracies in the parameter space of template fitting inevitable in the presence of a few bands.
We present the first weak gravitational lensing analysis of the completed Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). We study the 64 deg super(2) W1 field, the largest of the CFHTLS-Wide ...survey fields, and present the largest contiguous weak lensing convergence "mass map" yet made. 2.66 million galaxy shapes are measured, using the Kaiser Squires and Broadhurst Method (KSB) pipeline verified against high-resolution Hubble Space Telescope imaging that covers part of the CFHTLS. Our i'-band measurements are also consistent with an analysis of independent r'-band imaging. The reconstructed lensing convergence map contains 301 peaks with signal-to-noise ratio nu > 3.5, consistent with predictions of a LambdaCDM model. Of these peaks, 126 lie within 3'.0 of a brightest central galaxy identified from multicolor optical imaging in an independent, red sequence survey. We also identify seven counterparts for massive clusters previously seen in X-ray emission within 6 deg super(2) XMM-Lss survey. With photometric redshift estimates for the source galaxies, we use a tomographic lensing method to fit the redshift and mass of each convergence peak. Matching these to the optical observations, we confirm 85 groups/clusters with chi super(2) sub(reduced) < 3.0, at a mean redshift left angle bracketz sub(c)right angle bracket = 0.36 and velocity dispersion left angle bracketsigma sub()cright angle bracket = 658.8 km s super(-1). Future surveys, such as DES, LssT, KDUST, and EUCLID, will be able to apply these techniques to map clusters in much larger volumes and thus tightly constrain cosmological models.
Abstract
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 have been no known ...structures identified by more than two spectroscopically confirmed quiescent galaxies at
z
> 2.5. In this letter, we report the discovery of an overdense structure of massive quiescent galaxies with the spectroscopic redshift
z
= 2.77 in the COSMOS field, QO-1000. We first photometrically identify this structure as a 4.2
σ
overdensity with 14 quiescent galaxies in 7 × 4 pMpc
2
from the COSMOS2020 catalog. We then securely confirm the spectroscopic redshifts of four quiescent galaxies by detecting multiple Balmer absorption lines with Keck/MOSFIRE. All the spectroscopically confirmed members are massive (
log
(
M
⋆
/
M
⊙
)
>
11.0
) and located in a narrow redshift range (2.76 <
z
< 2.79). Moreover, three of them are in the 1 × 1 pMpc
2
in the transverse direction at the same redshift (
z
= 2.760–2.763). Such a concentration of four spectroscopically confirmed quiescent galaxies implies that QO-1000 is >68 times denser than the general field. In addition, we confirm that they form a red sequence in the
J
−
K
s
color. This structure’s halo mass is estimated as
log
(
M
halo
/
M
⊙
)
>
13.2
from its stellar mass. Similar structures found in the IllustrisTNG simulation are expected to evolve into massive galaxy clusters with
log
(
M
halo
/
M
⊙
)
≥
14.8
at
z
= 0. These results suggest that QO-1000 is a more mature protocluster than the other known protoclusters. It is likely in a transition phase between star-forming protoclusters and quenched galaxy clusters.
Abstract To study the role of environment in galaxy evolution, we reconstruct the underlying density field of galaxies based on COSMOS2020 (The Farmer catalog) and provide the density catalog for a ...magnitude-limited ( K s < 24.5) sample of ∼210,000 galaxies at 0.4 < z < 5 within the COSMOS field. The environmental densities are calculated using a weighted kernel density estimation approach with the choice of a von Mises–Fisher kernel, an analog of the Gaussian kernel for periodic data. Additionally, we make corrections for the edge effect and masked regions in the field. We utilize physical properties extracted by LePhare to investigate the connection between star formation activity and the environmental density of galaxies in six mass-complete subsamples at different cosmic epochs within 0.4 < z < 4. Our findings confirm a strong anticorrelation between star formation rate (SFR)/specific SFR (sSFR) and environmental density out to z ∼ 1.1. At 1.1 < z < 2, there is no significant correlation between SFR/sSFR and density. At 2 < z < 4, we observe a reversal of the SFR/sSFR–density relation such that both SFR and sSFR increase by a factor of ∼10 with increasing density contrast, δ , from −0.4 to 5. This observed reversal at higher redshifts supports the scenario where an increased availability of gas supply, along with tidal interactions and a generally higher star formation efficiency in dense environments, could potentially enhance star formation activity in galaxies located in rich environments at z > 2.
Using data from the COSMOS survey, we perform the first joint analysis of galaxy-galaxy weak lensing, galaxy spatial clustering, and galaxy number densities. Carefully accounting for sample variance ...and for scatter between stellar and halo mass, we model all three observables simultaneously using a novel and self-consistent theoretical framework. Our results provide strong constraints on the shape and redshift evolution of the stellar-to-halo mass relation (SHMR) from z = 0.2 to z = 1. We use simple arguments to show how the result raises the possibility that star formation quenching may ultimately depend on Msubh/Msub * and not simply on Msubh, as is commonly assumed. We show that simple models with such a dependence naturally lead to downsizing in the sites of star formation. Finally, we discuss the implications of our results in the context of popular quenching models, including disk instabilities and active galactic nucleus feedback.
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