ABSTRACT We present statistics of 133 faint 1.2 mm continuum sources detected in about 120 deep Atacama Large Millimeter/submillimeter Array (ALMA) pointing data that include all the archival deep ...data available by 2015 June. We derive number counts of 1.2 mm continuum sources down to 0.02 mJy partly with the assistance of gravitational lensing, and find that the total integrated 1.2 mm flux of the securely identified sources is Jy deg−2 which corresponds to of the extragalactic background light (EBL) measured by Cosmic Background Explorer observations. These results suggest that the major 1.2 mm EBL contributors are sources with 0.02 mJy, and that very faint 1.2 mm sources with 0.02 mJy contribute negligibly to the EBL with the possible flattening and/or truncation of number counts in this very faint flux regime. To understand the physical origin of our faint ALMA sources, we measure the galaxy bias bg by the counts-in-cells technique, and place a stringent upper limit of bg < 3.5 that is not similar to bg values of massive distant red galaxies and submillimeter galaxies but comparable to those of UV-bright, star-forming BzK galaxies (sBzKs) and Lyman break galaxies (LBGs). Moreover, in the optical and near-infrared (NIR) deep fields, we identify optical-NIR counterparts for 59% of our faint ALMA sources, the majority of which have luminosities, colors, and the IRX-β relation the same as sBzKs and LBGs. We thus conclude that about a half of our faint ALMA sources are dust-poor, high-z galaxies as known as sBzKs and LBGs in optical studies, and that these faint ALMA sources are not miniature (U)LIRGs simply scaled down with the infrared brightness.
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.
The physical properties and elemental abundances of the interstellar medium in galaxies during cosmic reionization are important for understanding the role of galaxies in this process. We report the ...Atacama Large Millimeter/submillimeter Array detection of an oxygen emission line at a wavelength of 88 micrometers from a galaxy at an epoch about 700 million years after the Big Bang. The oxygen abundance of this galaxy is estimated at about one-tenth that of the Sun. The nondetection of far-infrared continuum emission indicates a deficiency of interstellar dust in the galaxy. A carbon emission line at a wavelength of 158 micrometers is also not detected, implying an unusually small amount of neutral gas. These properties might allow ionizing photons to escape into the intergalactic medium.
We present evidence that a region of high effective Ly optical depth at z ∼ 5.7 is associated with an underdense region at the tail end of cosmic reionization. We carried out a survey of Lyman-break ...Galaxies (LBGs) using Subaru Hyper Suprime-Cam in the field of the z = 5.98 quasar J0148+0600, whose spectrum presents an unusually long (∼160 cMpc) and opaque (τ 7) Ly trough at 5.5 ≤ z ≤ 5.9. LBG candidates were selected to lie within the redshift range of the trough, and the projected number densities were measured within 90 cMpc of the quasar sightline. The region within 8′ (or 19 cMpc) of the quasar position is the most underdense of the whole field. The significance of the presence of the void is estimated to be 99%. This is consistent with the significant deficit of Ly emitters (LAEs) at z = 5.72 reported by Becker et al. and suggests that the paucity of LAEs is not purely due to the removal of the Ly emission by the high opacity but reflects a real coherent underdensity of galaxies across the entire redshift range of the trough. These observations are consistent with scenarios in which large optical depth fluctuations arise due to fluctuations in the galaxy-dominant UV background or due to residual neutral islands that are expected from reionization that is completed at redshifts as low as z 5.5.
Abstract
We present N/O abundance ratios, ionization parameters q
ion, and oxygen abundances O/H for a total of 41 galaxies (11 individual galaxies and a 30-galaxy stack) including Lyα emitters and ...Lyman break galaxies at z ∼ 2, and investigate galaxy evolution from z ∼ 0 to 2 in conjunction with 208529 local galaxies from the Sloan Digital Sky Survey (SDSS) and nine green pea galaxies (GPs). In contrast with most of the recent studies, we obtain the N/O ratio, q
ion, and O/H measurements by direct T
e methods using O iii λ4363 and O iii λ1665 lines. Based on these reliable measurements, we find that there are z ∼ 2 galaxies with excesses of N/O falling beyond the N/O–O/H relation of the local galaxies while the majority of the z ∼ 2 galaxies have N/O ratios that are nearly comparable with those of z ∼ 0 galaxies in the N/O–stellar mass relation. Our galaxies place the upper limit of the N/O ratio log(N/O) ≤ −1.26 on average, suggesting that the N/O ratio evolves, if at all, by <0.17 dex. Obtaining the reliable measurements free from the N/O–q
ion–O/H degeneracies, we demonstrate, for the first time, that z ∼ 2 galaxies with offsets in the Baldwin–Phillips–Terlevich (BPT) diagram show (1) only an N/O excess, (2) only a q
ion excess, or (3) both N/O and q
ion excesses. We argue that the BPT offsets at z ∼ 2 are not made by one of the (1)–(3) galaxy populations alone, but a composite of (1)–(3) populations. We confirm that these (1)–(3) populations also exist at z ∼ 0, such as GPs and SDSS low-mass and high-SFR galaxies (LMHSs).
Abstract
We present morphologies of galaxies at
z
≳ 9 resolved by JWST/NIRCam 2–5
μ
m imaging. Our sample consists of 22 galaxy candidates identified by stringent dropout and photo-
z
criteria in ...GLASS, CEERS, SMACS J0723, and Stephan’s Quintet flanking fields, one of which has been spectroscopically identified at
z
= 11.44. We perform surface brightness (SB) profile fitting with GALFIT for six bright galaxies with a signal-to-noise ratio = 10–40 on an individual basis and for stacked faint galaxies with secure point-spread functions (PSFs) of the NIRCam real data, carefully evaluating systematics by Monte Carlo simulations. We compare our results with those of previous JWST studies, and confirm that the effective radii
r
e
of our measurements are consistent with those of previous measurements at
z
∼ 9. We obtain
r
e
≃ 200–300 pc with the exponential-like profiles, Sérsic indexes of
n
≃ 1–1.5, for galaxies at
z
∼ 12–16, indicating that the relation of
r
e
∝ (1 +
z
)
s
for
s
=
−
1.22
−
0.16
+
0.17
explains cosmic evolution over
z
∼ 0–16 for
∼
L
z
=
3
*
galaxies. One bright (
M
UV
= −21 mag) galaxy at
z
∼ 12, GL-z12-1, has an extremely compact profile with
r
e
= 39 ± 11 pc that is surely extended over the PSF. Even in the case that the GL-z12-1 SB is fit by active galactic nuclei + galaxy composite profiles, the best-fit galaxy component is again compact,
r
e
=
48
−
15
+
38
pc, which is significantly (>5
σ
) smaller than the typical
r
e
value at
z
∼ 12. Compared with numerical simulations, we find that such a compact galaxy naturally forms at
z
≳ 10, and that frequent mergers at the early epoch produce more extended galaxies following the
r
e
∝ (1 +
z
)
s
relation.
We report 14 and 26 protocluster candidates at z = 5.7 and 6.6 over 14 and 16 deg2 areas, respectively, selected from 2230 (259) Ly emitters (LAEs) photometrically (spectroscopically) identified ...using Subaru/Hyper Suprime-Cam (HSC) deep images (Keck, Subaru, and Magellan spectra, and literature data). Six out of the 40 protocluster candidates include one to 13 spectroscopically confirmed LAEs. We conduct Monte Carlo simulations to estimate how many protocluster candidates are found by chance for randomly distributed sources, and find that the effective number of protocluster candidates at z = 5.7 (6.6) is six (five). By comparing with the cosmological Ly radiative transfer (RT) model reproducing the LAEs with reionization effects, we find that more than half of these protocluster candidates are progenitors of present-day clusters with mass of . We then investigate the correlation between the LAE overdensity δ and the Ly rest-frame equivalent width , because the cosmological Ly RT model suggests that the slope of the -δ relation steepens toward the epoch of cosmic reionization (EoR), due to the existence of ionized bubbles around galaxy overdensities easing the escape of Ly emission from the partly neutral intergalactic medium. The available HSC data suggest that the slope of the -δ correlation does not evolve from the post-reionization epoch, z = 5.7, to the EoR, z = 6.6, beyond the moderately large statistical errors. There is a possibility that we could detect the evolution of the -δ relation from z = 5.7 to 7.3 using the upcoming HSC observations that will provide large samples of LAEs at z = 6.6-7.3.
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 deep Keck/MOSFIRE near-infrared spectroscopy of a strong Ly
α
emitting source at
z
= 6.1292, HSC J142331.71−001809.1, which was discovered by the SHELLQS program from imaging data ...of the Subaru Hyper Suprime-Cam (HSC) survey. This source is one of five objects that show narrow (FWHM < 500 km s
−1
) and prominent (
L
Ly
α
> 10
44
erg s
−1
) Ly
α
emission lines at absolute 1450 Å continuum magnitudes of
M
1450
∼ −22 mag. Its rest-frame Ly
α
equivalent width (EW) is 370 ± 30 Å. In the 2 hr Keck/MOSFIRE spectrum in
Y
band, the high-ionization C
iv
λλ
1548,1550 doublet emission line was clearly detected with
FWHM
=
120
−
20
+
20
km s
−1
and a total rest-frame EW of
37
−
5
+
6
Å. We also report the detection of weak continuum emission, and the tentative detection of O
iii
λλ
1661,1666 in the 4 hr
J
-band spectrum. Judging from the UV magnitude, line widths, luminosities, and EWs of Ly
α
and C
iv
, we suggest that this source is a reionization-era analog of classical type-II AGNs, although there is a possibility that it represents a new population of AGN/galaxy composite objects in the early universe. We compare the properties of J1423−0018 to intermediate-redshift type-II AGNs and C
iv
emitters seen in
z
= 6–7 galaxy samples. Further observations of other metal emission lines in the rest-frame UV or optical, along with X-ray follow-up observations of the
z
= 6–7 narrow-line quasars, are needed for more robust diagnostics and to determine their nature.
We report the rest-frame ultraviolet luminosity function of g-dropout galaxies in 177 protocluster candidates (PC UVLF) at z ∼ 4 selected in the Hyper Suprime-Cam Subaru Strategic Program. Comparing ...it with the UVLF of field galaxies at the same redshift, we find that the PC UVLF shows a significant excess toward the bright end. This excess cannot be explained by the contribution of only active galactic nuclei, and we also find that this excess is more significant in higher density regions. Assuming that all protocluster members are located on the star formation main sequence, the PC UVLF can be converted into a stellar mass function. Consequently, our protocluster members are inferred to have a 2.8 times more massive characteristic stellar mass than that of the field Lyman break galaxies at the same redshift. This study, for the first time, clearly shows that the enhancement in star formation or stellar mass in overdense regions can generally be seen as early as at z ∼ 4. We also estimate the star formation rate density (SFRD) in protocluster regions as 6%-20% of the cosmic SFRD, based on the measured PC UVLF after correction for the selection incompleteness in our protocluster sample. This high value suggests that protoclusters make a nonnegligible contribution to the cosmic SFRD at z ∼ 4, as previously suggested by simulations. Our results suggest that protoclusters are essential components for galaxy evolution at z ∼ 4.
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