Abstract
We present the galaxy size−mass (
R
e
–
M
*
) distributions using a stellar mass complete sample of ∼1.5 million galaxies, covering ∼100 deg
2
, with
log
(
M
*
/
M
⊙
)
>
10.2
(
9.2
)
over ...the redshift range 0.2 <
z
< 1.0 (
z
< 0.6) from the second public data release of the Hyper Suprime-Cam Subaru Strategic Program. We confirm that, at fixed redshift and stellar mass over the range of
log
(
M
*
/
M
⊙
)
<
11
, star-forming galaxies are on average larger than quiescent galaxies. The large sample of galaxies with accurate size measurements, thanks to the excellent imaging quality, also enables us to demonstrate that the
R
e
–
M
*
relations of both populations have a form of a broken power law, with a clear change of slopes at a pivot stellar mass
M
p
. For quiescent galaxies, below an (evolving) pivot mass of
log
(
M
p
/
M
⊙
)
=
10.2
–
10.6
, the relation follows
R
e
∝
M
∗
0.1
; above
M
p
the relation is steeper and follows
R
e
∝
M
*
0.6
–
0.7
. For star-forming galaxies, below
log
(
M
p
/
M
⊙
)
∼
10.7
the relation follows
R
e
∝
M
*
0.2
; above
M
p
the relation evolves with redshift and follows
R
e
∝
M
*
0.3
–
0.6
. The shallow power-law slope for quiescent galaxies below
M
p
indicates that
large
low-mass quiescent galaxies have sizes similar to those of their counterpart star-forming galaxies. We take this as evidence that large low-mass quiescent galaxies have been recently quenched (presumably through environment-specific processes) without significant structural transformation. Interestingly, the pivot stellar mass of the
R
e
–
M
*
relations for both populations also coincides with the mass at which half of the galaxy population is quiescent, implying that the pivot mass represents the transition of galaxy growth from being dominated by in situ star formation to being dominated by (dry) mergers.
Abstract
We study the physical properties of the ionized gas in local discs using the sample of 38 nearby ∼108.5–11.2 M⊙ Star-Forming Main-Sequence (SFMS) galaxies observed so far as part of the MUSE ...Atlas of Disks (MAD). Specifically, we use all strong emission lines in the MUSE wavelength range 4650–9300 Å to investigate the resolved ionized gas properties on ∼100 pc scales. This spatial resolution enables us to disentangle H ii regions from the diffuse ionized gas (DIG) in the computation of gas metallicities and star formation rates (SFRs) of star-forming regions. The gas metallicities generally decrease with radius. The metallicity of the H ii regions is on average ∼0.1 dex higher than that of the DIG, but the metallicity radial gradient in both components is similar. The mean metallicities within the inner galaxy cores correlate with the total stellar mass of the galaxies. On our < 100 pc scales, we find two correlations previously reported at kpc scales: a spatially resolved mass–metallicity relation (RMZR) and a spatially resolved SFMS (RSFMS). We find no secondary dependence of the RMZR with the SFR density. We find that both resolved relations have a local origin, as they do not depend on the total stellar mass. The observational results of this paper are consistent with the inside-out scenario for the growth of galactic disks.
We present the first stellar velocity dispersion measurement of a massive quenching galaxy at z = 4. The galaxy is first identified as a massive z ≥ 4 galaxy with suppressed star formation from ...photometric redshifts based on deep multiband data. A follow-up spectroscopic observation with MOSFIRE on Keck revealed strong multiple absorption features, which are identified as Balmer lines, giving a secure redshift of z = 4.01. This is the most distant quiescent galaxy known to date. Thanks to the high S/N of the spectrum, we are able to estimate the stellar velocity dispersion, , making a significant leap from the previous highest redshift measurement at z = 2.8. Interestingly, we find that the velocity dispersion is consistent with that of massive galaxies today, implying no significant evolution in velocity dispersion over the last 12 Gyr. Based on a stringent upper limit on its physical size from deep optical images (reff < 1.3 kpc), we find that its dynamical mass is consistent with the stellar mass inferred from photometry. Furthermore, the galaxy is located on the mass fundamental plane extrapolated from lower redshift galaxies. The observed no strong evolution in suggests that the mass in the core of massive galaxies does not evolve significantly, while most of the mass growth occurs in the outskirts of the galaxies, which also increases the size. This picture is consistent with a two-phase formation scenario in which mass and size growth is due to accretion in the outskirts of galaxies via mergers. Our results imply that the first phase may be completed as early as z ∼ 4.
We investigate the multi-wavelength properties of host galaxies of 3701 X-ray-selected active galactic nuclei (AGNs) out to z ∼ 5 in the Chandra-COSMOS Legacy Survey. Thanks to the extensive ...multi-wavelength photometry available in the COSMOS field, we derive AGN luminosities, host stellar masses, and star formation rates (SFRs) via a multi-component SED fitting technique. Type 1 and Type 2 AGNs follow the same intrinsic L2-10 keV-L6 m relation, suggesting that mid-infrared emission is a reasonably good measure of the AGN accretion power regardless of obscuration. We find that there is a strong increase in Type 1 AGN fraction toward higher AGN luminosity, possibly due to the fact that Type 1 AGNs tend to be hosted by more massive galaxies. The AGN luminosity and SFR are consistent with an increase toward high stellar mass, while the Mstellar dependence is weaker toward the high-mass end, which could be interpreted as a consequence of quenching both star formation and AGN activity in massive galaxies. AGN host galaxies tend to have SFRs that are consistent with normal star-forming galaxies, independent of AGN luminosities. We confirm that black hole accretion rate and SFR are correlated up to z ∼ 5, when forming stars. The majority (∼73%) of our AGN sample are faint in the far-infrared, implying that the moderate-luminosity AGNs seem to be still active after the star formation is suppressed. It is not certain whether AGN activity plays a role in quenching the star formation. We conclude that both AGN activity and star formation might be more fundamentally related to host stellar mass.
Abstract
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 ∼145 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 ∼80 candidate quiescent and quenching galaxies at 3 <
z
< 5 using two methods: (1) based on their rest-frame
UVJ
colors, and (2) a novel quantitative approach based on Gaussian mixture modeling of the near-UV −
U
,
U
−
V
, and
V
−
J
rest-frame color space, which is more sensitive to recently quenched objects. We measure comoving number densities of massive (
M
⋆
≥ 10
10.6
M
⊙
) quiescent galaxies consistent with previous estimates relying on ground-based observations, after homogenizing the results in the literature with our mass and redshift intervals. However, we find significant field-to-field variations of the number densities up to a factor of 2–3, highlighting the effect of cosmic variance and suggesting the presence of overdensities of red quiescent galaxies at
z
> 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.
Abstract
We present optical-line gas metallicity diagnostics established by the combination of local SDSS galaxies and the largest compilation of extremely metal-poor galaxies (EMPGs) including new ...EMPGs identified by the Subaru EMPRESS survey. A total of 103 EMPGs are included, covering a large parameter space of magnitude (
M
i
= −19 to −7) and H
β
equivalent width (10–600 Å), i.e., wide ranges of stellar mass and star formation rate. Using reliable metallicity measurements from the direct method for these galaxies, we derive the relationships between strong optical-line ratios and gas-phase metallicity over the range of
12
+
log
(
O
/
H
)
≃ 6.9–8.9, corresponding to 0.02–2 solar metallicity
Z
⊙
. We confirm that the R23 index, (O
iii
+O
ii
)/H
β
, is the most accurate metallicity indicator with a metallicity uncertainty of 0.14 dex over the range among various popular metallicity indicators. The other metallicity indicators show large scatters in the metal-poor range (≲0.1
Z
⊙
). It is explained by our
CLOUDY
photoionization modeling that, unlike the R23 index, the other metallicity indicators do not use a sum of singly and doubly ionized lines and cannot trace both low- and high-ionization gas. We find that the accuracy of the metallicity indicators is significantly improved if one uses H
β
equivalent width measurements that tightly correlate with ionization states. In this work, we also present the relation of physical properties with the UV-continuum slope
β
and ionization production rate
ξ
ion
derived with GALEX data for the EMPGs and provide local anchors of galaxy properties together with the optical-line metallicity indicators that are available in the form of a machine-readable table and useful for forthcoming JWST spectroscopic studies.
We study the history from to of the stellar mass assembly of quiescent and star-forming galaxies in a spatially resolved fashion. For this purpose, we use multi-wavelength imaging data from the ...Hubble Space Telescope (HST) over the GOODS fields and the Sloan Digital Sky Survey (SDSS) for the local population. We present the radial stellar mass surface density profiles of galaxies with , corrected for mass-to-light ratio ( /L) variations, and derive the half-mass-radius (Rm), central stellar mass surface density within 1 kpc ( ) and surface density at Rm ( ) for star-forming and quiescent galaxies and study their evolution with redshift. At fixed stellar mass, the half-mass sizes of quiescent galaxies increase from to by a factor of , whereas the half-mass sizes of star-forming galaxies increase only slightly, by a factor of ∼2. The central densities of quiescent galaxies decline slightly (by a factor of ) from to , while for star-forming galaxies increases with time, at fixed mass. We show that the central density has a tighter correlation with specific star-formation rate (sSFR) than and for all masses and redshifts galaxies with higher central density are more prone to be quenched. Reaching a high central density ( ) seems to be a prerequisite for the cessation of star formation, though a causal link between high and quenching is difficult to prove and their correlation can have a different origin.
ABSTRACT
We study structural properties of spectroscopically confirmed massive quiescent galaxies at z ≈ 3 with one of the first sizeable samples of such sources, made of ten 10.8 < log (M⋆/M⊙) < ...11.3 galaxies at 2.4 < z < 3.2 in the COSMOS field whose redshifts and quiescence are confirmed by Hubble Space Telescope (HST) grism spectroscopy. Although affected by a weak bias toward younger stellar populations, this sample is deemed to be largely representative of the majority of the most massive and thus intrinsically rarest quiescent sources at this cosmic time. We rely on targeted HST/Wide-Field Camera 3 observations and fit Sérsic profiles to the galaxy surface brightness distributions at $\approx {4000}\hbox{-}{\, {\mathring{\rm A}}}$ rest frame. We find typically high Sérsic indices and axis ratios (medians ≈ 4.5 and 0.73, respectively) suggesting that, at odds with some previous results, the first massive quiescent galaxies may largely be already bulge-dominated systems. We measure compact galaxy sizes with an average of $\approx {1.4}\, {\rm kpc}$ at log (M⋆/M⊙) ≈ 11.2, in good agreement with the extrapolation at the highest masses of previous determinations of the stellar mass–size relation of quiescent galaxies, and of its redshift evolution, from photometrically selected samples at lower and similar redshifts. This work confirms the existence of a population of compact, bulge dominated, massive, quiescent sources at z ≈ 3, providing one of the first statistical estimates of their structural properties, and further constraining the early formation and evolution of the first quiescent galaxies.
Abstract
We present the selection, spectroscopic identification, and physical properties of extreme emission-line galaxies (EELGs) at 3 <
z
< 3.7, aiming at studying physical properties of an ...analog population of star-forming galaxies (SFGs) at the epoch of reionization. The sample is selected based on the excess in the observed
Ks
broadband flux relative to the best-fit stellar continuum model flux. By applying a 0.3 mag excess as a primary criterion, we select 240 EELG candidates with intense emission lines and estimated an observed-frame equivalent width (EW) of ≳1000 Å over the UltraVISTA-DR2 ultra-deep stripe in the COSMOS field. We then carried out
HK
-band follow-up spectroscopy for 23 of the candidates with Subaru/MOIRCS, and we find that 19 and 2 of them are at
z
> 3 with intense O
iii
emission and H
α
emitters at
z
≃ 2, respectively. These spectroscopically identified EELGs at
z
≃ 3.3 show, on average, higher specific star formation rates (sSFRs) than the star-forming main sequence, low dust attenuation of
E
(
B
−
V
) ≲ 0.1 mag, and high O
iii
/O
ii
ratios of ≳3. We also find that our EELGs at
z
≃ 3.3 have higher hydrogen-ionizing photon production efficiencies (
ξ
ion
) than the canonical value (≃10
25.2
erg
−1
Hz), indicating that they are efficient in ionizing their surrounding interstellar medium. These physical properties suggest that they are low-metallicity galaxies with higher ionizing parameters and harder UV spectra than normal SFGs, which is similar to galaxies with Lyman continuum (LyC) leakage. Among our EELGs, those with the largest O
iii
/O
ii
and EW(O
iii
) values would be the most promising candidates to search for LyC leakage.
Abstract
We present gas-phase elemental abundance ratios of thirteen local extremely metal-poor galaxies (EMPGs), including our new Keck/LRIS spectroscopy determinations together with 33 James Webb ...Space Telescope
z
∼ 4–10 star-forming galaxies in the literature, and compare chemical evolution models. We develop chemical evolution models with the yields of core-collapse supernovae (CCSNe), Type Ia SNe, hypernovae (HNe), and pair-instability supernovae (PISNe), and compare the EMPGs and high-
z
galaxies in conjunction with dust depletion contributions. We find that high Fe/O values of EMPGs can (cannot) be explained by PISN metal enrichments (CCSN/HN enrichments even with the mixing-and-fallback mechanism enhancing iron abundance), while the observed Ar/O and S/O values are much smaller than the predictions of the PISN models. The abundance ratios of EMPGs can be explained by the combination of Type Ia SNe and CCSNe/HNe whose inner layers of argon and sulfur mostly fallback, which are comparable to the Sculptor stellar chemical abundance distribution, suggesting that early chemical enrichment has taken place in the EMPGs. Comparing our chemical evolution models with the star-forming galaxies at
z
∼ 4–10, we find that the Ar/O and S/O ratios of the high-
z
galaxies are comparable to those of the CCSN/HN models, while the majority of high-
z
galaxies do not have constraints good enough to rule out contributions from PISNe. The high N/O ratio recently reported in GN-z11 cannot be explained even by rotating PISNe, but could be reproduced by the winds of rotating Wolf–Rayet stars that end up as a direct collapse.
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