ABSTRACT
Recent work has suggested that extreme O iii emitting star-forming galaxies are important to reionization. Relatedly, O iii/O ii has been put forward as an indirect estimator of the Lyman ...Continuum (LyC) escape fraction (fesc) at z ≳ 4.5 when the opaque IGM renders LyC photons unobservable. Using deep archival U-band (VLT/VIMOS) imaging of a recently confirmed overdensity at z∼ 3.5, we calculate tight constraints on fesc for a sample (N = 73) dominated by extreme O iii emitters. We find no LyC signal ($f_{\rm esc}^{\rm rel} < 6.3^{+0.7}_{-0.7} \hbox{ per cent}$ at 1σ) in a deep U-band stack of our sample (31.98 mag at 1σ). This constraint is in agreement with recent studies of star-forming galaxies spanning z ∼ 1–4 that have found very low average fesc. Despite the galaxies in our study having an estimated average rest-frame EW(O iiiλ5007) ∼ 400 Å and O iii/O ii ∼ 4 from composite SED fitting, we find no LyC detection, which brings into question the potential of O iii/O ii as an effective probe of the LyC – a majority of LyC emitters have O iii/O ii > 3, but we establish here that O iii/O ii > 3 does not guarantee significant LyC leakage for a population. Since even extreme star-forming galaxies are unable to produce the $f_{\rm esc}\sim 10{-}15\hbox{ per cent}$ required by most theoretical calculations for star-forming galaxies to drive reionization, there must either be a rapid evolution of fesc between z∼ 3.5 and the epoch of reionization, or hitherto observationally unstudied sources e.g. ultrafaint low-mass galaxies with log (M/M⊙) ∼ 7–8.5 must make an outsized contribution to reionization.
Abstract
We present near-infrared spectroscopic confirmations of a sample of 16 photometrically selected galaxies with stellar masses
>11 at redshift
z
> 3 from the XMM-VIDEO and COSMOS-UltraVISTA ...fields using Keck/MOSFIRE as part of the Massive Ancient Galaxies At
z
> 3 NEar-infrared (MAGAZ3NE) survey. Eight of the ultramassive galaxies (UMGs) have specific star formation rates (sSFR) < 0.03 Gyr
−1
, with negligible emission lines. Another seven UMGs show emission lines consistent with active galactic nuclei and/or star formation, while only one UMG has sSFR > 1 Gyr
−1
. Model star formation histories of these galaxies describe systems that formed the majority of their stars in vigorous bursts of several hundred megayear duration around
during which hundreds to thousands of solar masses were formed per year. These formation ages of <1 Gyr prior to observation are consistent with ages derived from measurements of
D
n
(4000) and
(H
δ
). Rapid quenching followed these bursty star-forming periods, generally occurring less than 350 Myr before observation, resulting in post-starburst SEDs and spectra for half the sample. The rapid formation timescales are consistent with the extreme star formation rates observed in
dusty starbursts observed with ALMA, suggesting that such dusty galaxies are progenitors of these UMGs. While such formation histories have been suggested in previous studies, the large sample introduced here presents the most compelling evidence yet that vigorous star formation followed by rapid quenching is almost certainly the norm for high-mass galaxies in the early universe. The UMGs presented here were selected to be brighter than
K
s
= 21.7, raising the intriguing possibility that even (fainter) older quiescent UMGs could exist at this epoch.
Abstract
How massive early-type galaxies (ETGs) assembled their mass, on which timescales the star formation quenched, and when their supersolar metallicity has been established are still open and ...debated issues. Thanks to very deep spectroscopic observations carried out at the Large Binocular Telescope, we simultaneously measured stellar age, metallicity, and velocity dispersion for C1-23152, an ETG at redshift
z
= 3.352, corresponding to an epoch when the universe was ∼1.8 Gyr old. The analysis of its spectrum shows that this galaxy, hosting an active galactic nucleus (AGN), formed and assembled ∼2 × 10
11
M
⊙
, shaping its morphology within the ∼600 Myr preceding the observations, since
z
∼ 4.6. The stellar population has a mean mass-weighted age of
Myr, and it is formed between ∼600 and ∼150 Myr before the observed epoch, the latter being the time since quenching. Its high stellar velocity dispersion,
σ
e
= 409 ± 60 km s
−1
, confirms the high mass (
M
dyn
= 2.2 (±0.4) × 10
11
M
⊙
) and the high mass density (
= Σ
1kpc
= 3.2 (±0.7) × 10
10
M
⊙
kpc
−2
), suggesting a fast dissipative process at its origin. The analysis points toward a supersolar metallicity, Z/H = 0.25
, in agreement with the above picture, suggesting a star formation efficiency much higher than the replenishment time. However, subsolar-metallicity values cannot be firmly ruled out by our analysis. Quenching must have been extremely efficient to reduce the star formation to SFR < 6.5
M
⊙
yr
−1
in less than 150 Myr. This could be explained by the presence of the AGN, even if a causal relation cannot be established from the data. C1-23152 has the same stellar and physical properties of the densest ETGs in the local universe of comparable mass, suggesting that they are C1-23152-like galaxies that evolved to
z
= 0 unperturbed.
Abstract
We study galactic star formation activity as a function of environment and stellar mass over 0.5 <
z
< 2.0 using the FourStar Galaxy Evolution (ZFOURGE) survey. We estimate the galaxy ...environment using a Bayesian-motivated measure of the distance to the third nearest neighbor for galaxies to the stellar mass completeness of our survey,
at
z
= 1.3 (2.0). This method, when applied to a mock catalog with the photometric-redshift precision (
) of ZFOURGE, accurately recovers galaxies in low- and high-density environments. We quantify the environmental quenching efficiency and show that at
, it depends on galaxy stellar mass, demonstrating that the effects of quenching related to (stellar) mass and environment are not separable. In high-density environments, the mass and environmental quenching efficiencies are comparable for massive galaxies (
) at all redshifts. For lower-mass galaxies (
), the environmental quenching efficiency is very low at
, but increases rapidly with decreasing redshift. Environmental quenching can account for nearly all quiescent lower-mass galaxies (
), which appear primarily at
. The morphologies of lower-mass quiescent galaxies are inconsistent with those expected of recently quenched star-forming galaxies. Some environmental process must transform the morphologies on similar timescales as the environmental quenching itself. The evolution of the environmental quenching favors models that combine gas starvation (as galaxies become satellites) with gas exhaustion through star formation and outflows (“overconsumption”), and additional processes such as galaxy interactions, tidal stripping, and disk fading to account for the morphological differences between the quiescent and star-forming galaxy populations.
We study the stellar mass functions (SMFs) of star-forming and quiescent galaxies in 11 galaxy clusters at 1.0 <
z
< 1.4 drawn from the Gemini Observations of Galaxies in Rich Early ENvironments ...(GOGREEN) survey. Based on more than 500 h of Gemini/GMOS spectroscopy and deep multi-band photometry taken with a range of observatories, we probe the SMFs down to a stellar mass limit of 10
9.7
M
⊙
(10
9.5
M
⊙
for star-forming galaxies). At this early epoch, the fraction of quiescent galaxies is already highly elevated in the clusters compared to the field at the same redshift. The quenched fraction excess (QFE) represents the fraction of galaxies that would be star-forming in the field but are quenched due to their environment. The QFE is strongly mass dependent, and increases from ∼30% at
M
⋆
= 10
9.7
M
⊙
to ∼80% at
M
⋆
= 10
11.0
M
⊙
. Nonetheless, the shapes of the SMFs of the two individual galaxy types, star-forming and quiescent galaxies, are identical between cluster and field to high statistical precision. Nevertheless, along with the different quiescent fractions, the total galaxy SMF is also environmentally dependent, with a relative deficit of low-mass galaxies in the clusters. These results are in stark contrast with findings in the local Universe, and therefore require a substantially different quenching mode to operate at early times. We discuss these results in light of several popular quenching models.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
Abstract
We present spectra of the most massive quiescent galaxy yet spectroscopically confirmed at
z
> 3, verified via the detection of Balmer absorption features in the
H
- and
K
-bands of ...Keck/MOSFIRE. The spectra confirm a galaxy with no significant ongoing star formation, consistent with the lack of rest-frame UV flux and overall photometric spectral energy distribution. With a stellar mass of
at
z
= 3.493, this galaxy is nearly three times more massive than the highest redshift spectroscopically confirmed absorption-line-identified galaxy known. The star formation history of this quiescent galaxy implies that it formed >1000
M
⊙
yr
−1
for almost 0.5 Gyr beginning at
z
∼ 7.2, strongly suggestive that it is the descendant of massive dusty star-forming galaxies at 5 <
z
< 7 recently observed with ALMA. While galaxies with similarly extreme stellar masses are reproduced in some simulations at early times, such a lack of ongoing star formation is not seen there. This suggests the need for a quenching process that either starts earlier or is more rapid than that currently prescribed, challenging our current understanding of how ultra-massive galaxies form and evolve in the early universe.
We study the effects of galaxy environment on the evolution of the stellar mass function (SMF) over 0.2 < z < 2.0 using the FourStar Galaxy Evolution (ZFOURGE) Survey and NEWFIRM Medium-Band Survey ...(NMBS) down to the stellar mass completeness limit, (9.5) at z = 1.0 (2.0). We compare the SMFs for quiescent and star-forming galaxies in the highest and lowest environments using a density estimator based on the distance to the galaxies' third-nearest neighbors. For star-forming galaxies, at all redshifts there are only minor differences with environment in the shape of the SMF. For quiescent galaxies, the SMF in the lowest densities shows no evolution with redshift other than an overall increase in number density (φ*) with time. This suggests that the stellar mass dependence of quenching in relatively isolated galaxies both is universal and does not evolve strongly. While at , the SMF of quiescent galaxies is indistinguishable in the highest and lowest densities, at lower redshifts, it shows a rapidly increasing number density of lower-mass galaxies, , in the highest-density environments. We argue that this evolution can account for all the redshift evolution in the shape of the total quiescent galaxy SMF. This evolution in the quiescent galaxy SMF at higher redshift (z > 1) requires an environmental quenching efficiency that decreases with decreasing stellar mass at 0.5 < z < 1.5 or it would overproduce the number of lower-mass quiescent galaxies in denser environments. This requires a dominant environmental process such as starvation combined with rapid gas depletion and ejection at z > 0.5-1.0 for galaxies in our mass range. The efficiency of this process decreases with redshift, allowing other processes (such as galaxy interactions and ram-pressure stripping) to become more important at later times, z < 0.5.
Abstract
We present the census of massive (log(
M
*
/
M
⊙
) > 11) galaxies at 3 <
z
< 6 identified over the COSMOS/UltraVISTA Ultra-Deep field stripes: consisting of ≈100 and ≈20 high-confidence ...candidates at 3 <
z
< 4 and 4 <
z
< 6, respectively. The 3 <
z
< 4 population is comprised of post-starburst, UV-star-forming, and dusty star-forming galaxies in roughly equal fractions, while UV-star-forming galaxies dominate at 4 <
z
< 6 . We account for various sources of biases in the spectral energy distribution (SED) modeling, finding that the treatment of emission line contamination is essential for understanding the number densities and mass growth histories of massive galaxies at
z
> 3. The significant increase in observed number densities at
z
∼ 4 (> × 5 in ≲600 Myr) implies that this is the epoch at which log(
M
*
/
M
⊙
) > 11 galaxies emerge in significant numbers, with stellar ages (≈500–900 Myr) indicating rapid formation epochs as early as
z
∼ 7. Leveraging ancillary multiwavelength data sets, we perform panchromatic SED modeling to constrain the total star formation activity of the sample. The star formation activity of the sample is generally consistent with being on the star formation main sequence at the considered redshifts, with ≈15%–25% of the population showing evidence of suppressed star formation rates, indicating that quenching mechanisms are already at play by
z
∼ 4. We stack the available Hubble Space Telescope imaging, confirming their compact nature (
r
e
≲ 2.2 kpc), consistent with expected sizes of high-
z
star-forming galaxies. Finally, we discuss how our results are in-line with the early formation epochs and short formation timescales inferred from the fossil records of the most massive galaxies in the universe.
ABSTRACT
We study the star formation histories (SFHs) and mass-weighted ages of 331 UVJ-selected quiescent galaxies in 11 galaxy clusters and in the field at 1 < z < 1.5 from the Gemini Observations ...of Galaxies in Rich Early ENvironments (GOGREEN) survey. We determine the SFHs of individual galaxies by simultaneously fitting rest-frame optical spectroscopy and broad-band photometry to stellar population models. We confirm that the SFHs are consistent with more massive galaxies having on average earlier formation times. Comparing galaxies found in massive clusters with those in the field, we find galaxies with M* < 1011.3 M⊙ in the field have more extended SFHs. From the SFHs we calculate the mass-weighted ages, and compare age distributions of galaxies between the two environments, at fixed mass. We constrain the difference in mass-weighted ages between field and cluster galaxies to $0.31_{^{-0.33}}^{_{+0.51}}$ Gyr, in the sense that cluster galaxies are older. We place this result in the context of two simple quenching models and show that neither environmental quenching based on time since infall (without pre-processing) nor a difference in formation times alone can reproduce both the average age difference and relative quenched fractions. This is distinctly different from local clusters, for which the majority of the quenched population is consistent with having been environmentally quenched upon infall. Our results suggest that quenched population in galaxy clusters at z > 1 has been driven by different physical processes than those at play at z = 0.
Abstract
We investigate the properties of galaxies as they shut off star formation over the 4 billion years surrounding peak cosmic star formation. To do this, we categorize ∼7000 galaxies from 1 <
...z
< 4 into 90 groups based on the shape of their spectral energy distributions (SEDs) and build composite SEDs with
R
∼ 50 resolution. These composite SEDs show a variety of spectral shapes and also show trends in parameters such as color, mass, star formation rate, and emission-line equivalent width. Using emission-line equivalent widths and strength of the 4000 Å break,
, we categorize the composite SEDs into five classes: extreme emission line, star-forming, transitioning, post-starburst, and quiescent galaxies. The transitioning population of galaxies shows modest H
α
emission (EW
REST
∼ 40 Å) compared to more typical star-forming composite SEDs at log
10
(
M
/
M
⊙
) ∼ 10.5 (EW
REST
∼ 80 Å). Together with their smaller sizes (3 kpc vs. 4 kpc) and higher Sérsic indices (2.7 vs. 1.5), this indicates that morphological changes initiate before the cessation of star formation. The transitional group shows a strong increase of over 1 dex in number density from
z
∼ 3 to
z
∼ 1, similar to the growth in the quiescent population, while post-starburst galaxies become rarer at
z
≲ 1.5. We calculate average quenching timescales of 1.6 Gyr at
z
∼ 1.5 and 0.9 Gyr at
z
∼ 2.5 and conclude that a fast-quenching mechanism producing post-starbursts dominated the quenching of galaxies at early times, while a slower process has become more common since
z
∼ 2.
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