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.
Abstract
This paper systematically investigates the comoving megaparsec-scale intergalactic medium (IGM) environment around galaxies traced by the Ly
α
forest. Using our cosmological hydrodynamic ...simulations, we investigate the IGM–galaxy connection at
z
= 2 by two methods: (i) cross-correlation analysis between galaxies and the fluctuation of Ly
α
forest transmission (
δ
F
) and (ii) comparison of the overdensity of neutral hydrogen (H
i
) and galaxies. Our simulations reproduce observed cross-correlation functions (CCFs) between Ly
α
forest and Lyman-break galaxies. We further investigate the variation of the CCF using subsamples divided by dark matter halo mass (
M
DH
), galaxy stellar mass (
M
⋆
), and star formation rate (SFR) and find that the CCF signal becomes stronger with increasing
M
DH
,
M
⋆
, and SFR. The CCFs between galaxies and gas density fluctuation are also found to have similar trends. Therefore, the variation of
δ
F
–CCF depending on
M
DH
,
M
⋆
, and SFR is due to varying gas densities around galaxies. We find that the correlation between galaxies and the IGM H
i
distribution strongly depends on
M
DH
as expected from linear theory. Our results support the ΛCDM paradigm, confirming a spatial correlation between galaxies and IGM H
i
, with more massive galaxies being clustered in higher-density regions.
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.
Abstract
Deep Very Large Telescope/MUSE optical integral field spectroscopy has recently revealed an abundant population of ultra-faint galaxies (
M
UV
≈ −15; 0.01
L
⋆
) at
z
= 2.9−6.7 due to their ...strong Ly
α
emission with no detectable continuum. The implied Ly
α
equivalent widths can be in excess of 100–200 Å, challenging existing models of normal star formation and indicating extremely young ages, small stellar masses, and a very low amount of metal enrichment. We use JWST/NIRSpec’s microshutter array to follow up 45 of these galaxies (11 hr in G235M/F170LP and 7 hr in G395M/F290LP), as well as 45 lower-equivalent width Ly
α
emitters. Our spectroscopy covers the range 1.7−5.1 micron in order to target strong optical emission lines: H
α
, O
iii
, H
β
, and N II. Individual measurements as well as stacks reveal line ratios consistent with a metal-poor nature (2%−40%
Z
⊙
, depending on the calibration). The galaxies with the highest equivalent widths of Ly
α
, in excess of 90 Å, have lower N II/H
α
(1.9
σ
) and O
iii
/H
β
(2.2
σ
) ratios than those with lower equivalent widths, implying lower gas-phase metallicities at a combined significance of 2.4
σ
. This implies a selection based on Ly
α
equivalent width is an efficient technique for identifying younger, less chemically enriched systems.
Abstract
We present the morphology and stellar population of 27 extremely metal-poor galaxies (EMPGs) at
z
∼ 0 with metallicities of 0.01–0.1
Z
⊙
. We conduct multicomponent surface brightness (SB) ...profile fitting for the deep Subaru/Hyper Suprime-Cam
i
-band images of the EMPGs with the
Galfit
software, carefully removing the SB contributions of tails. We find that the EMPGs with a median stellar mass of
log
(
M
*
/
M
⊙
)
=
6.0
have a median Sérsic index of
n
= 1.1 and a median effective radius of
r
e
= 200 pc, suggesting that typical EMPGs have a very compact disk. We compare the EMPGs with
z
∼ 6 galaxies and local galaxies on the size–mass (
r
e
–
M
*
) diagram, and identify that the majority of the EMPGs have an
r
e
–
M
*
relation similar to
z
∼ 0 star-forming galaxies rather than
z
∼ 6 galaxies. Not every EMPG is a local analog of high-
z
young galaxies in the
r
e
–
M
*
relation. A spectrum of one pair of EMPG and tail, so far available, indicates that the tail is dynamically related to the EMPG with a median velocity difference of Δ
V
= 101 ± 32 km s
−1
. This moderately large Δ
V
cannot be explained by the dynamics of the tail, but likely by the infall on the tail. For the first time, we may identify the metal-poor star-forming system just now infalling into the tail.
Abstract
We present average stellar population properties and dark matter halo masses of z ∼ 2 Lyα emitters (LAEs) from spectral energy distribution fitting and clustering analysis, respectively, ...using ≃ 1250 objects ($\mathit {NB387}\le 25.5$) in four separate fields of ≃ 1 deg2 in total. With an average stellar mass of 10.2 ± 1.8 × 108 M⊙ and star formation rate of 3.4 ± 0.4 M⊙ yr−1, the LAEs lie on an extrapolation of the star-formation main sequence (MS) to low stellar mass. Their effective dark matter halo mass is estimated to be $4.0_{-2.9}^{+5.1} \times 10^{10}{\,\,}M_{\odot }$ with an effective bias of $1.22^{+0.16}_{-0.18}$, which is lower than that of z ∼ 2 LAEs (1.8 ± 0.3) obtained by a previous study based on a three times smaller survey area, with a probability of 96%. However, the difference in the bias values can be explained if cosmic variance is taken into account. If such a low halo mass implies a low H i gas mass, this result appears to be consistent with the observations of a high Lyα escape fraction. With the low halo masses and ongoing star formation, our LAEs have a relatively high stellar-to-halo mass ratio (SHMR) and a high efficiency of converting baryons into stars. The extended Press–Schechter formalism predicts that at z = 0 our LAEs are typically embedded in halos with masses similar to that of the Large Magellanic Cloud (LMC); they will also have similar SHMRs to the LMC, if their star formation rates are largely suppressed after z ∼ 2 as some previous studies have reported for the LMC itself.
Abstract
We present a new catalog of 9318 Ly
α
emitter (LAE) candidates at
z
= 2.2, 3.3, 4.9, 5.7, 6.6, and 7.0 that are photometrically selected by the SILVERRUSH program with a machine learning ...technique from large area (up to 25.0 deg
2
) imaging data with six narrowband filters taken by the Subaru Strategic Program with Hyper Suprime-Cam and a Subaru intensive program, Cosmic HydrOgen Reionization Unveiled with Subaru. We construct a convolutional neural network that distinguishes between real LAEs and contaminants with a completeness of 94% and a contamination rate of 1%, enabling us to efficiently remove contaminants from the photometrically selected LAE candidates. We confirm that our LAE catalogs include 177 LAEs that have been spectroscopically identified in our SILVERRUSH programs and previous studies, ensuring the validity of our machine learning selection. In addition, we find that the object-matching rates between our LAE catalogs and our previous results are ≃80%–100% at bright NB magnitudes of ≲24 mag. We also confirm that the surface number densities of our LAE candidates are consistent with previous results. Our LAE catalogs will be made public on our project webpage.
Abstract
We present 20,567 Ly
α
emitters (LAEs) at
z
= 2.2 − 7.3 that are photometrically identified by the SILVERRUSH program in a large survey area up to 25 deg
2
with deep images of five broadband ...filters (
grizy
) and seven narrowband filters targeting Ly
α
lines at
z
= 2.2, 3.3, 4.9, 5.7, 6.6, 7.0, and 7.3 taken by the Hyper Suprime-Cam Subaru Strategic Program and the Cosmic HydrOgen Reionization Unveiled with Subaru survey. We select secure >5
σ
sources showing narrowband color excesses via Ly
α
break screening, taking into account the spatial inhomogeneity of limiting magnitudes. After removing spurious sources by careful masking and visual inspection of coadded and multiepoch images obtained over the 7 yr of the surveys, we construct LAE samples consisting of 6995, 4641, 726, 6124, 2058, 18, and 5 LAEs at
z
= 2.2, 3.3, 4.9, 5.7, 6.6, 7.0, and 7.3, respectively, although the
z
= 7.3 candidates are tentative. Our LAE catalogs contain 289 spectroscopically confirmed LAEs at the expected redshifts from previous work. We demonstrate that the number counts of our LAEs are consistent with previous studies with similar LAE selection criteria. The LAE catalogs will be made public on our project webpage with detailed descriptions of the content and ancillary information about the masks and limiting magnitudes.
ABSTRACT
Subaru Strategic Program with the Hyper-Suprime Cam (HSC-SSP) has proven to be successful with its extremely wide area coverage in past years. Taking advantages of this feature, we report ...initial results from exploration and research of expansive over- and underdense structures at z = 0.3–1 based on the second Public Data Release where optical 5-band photometric data for ∼ eight million sources with i < 23 mag are available over ∼360 deg2. We not only confirm known superclusters but also find candidates of titanic over- and underdense regions out to z = 1. The mock data analysis suggests that the density peaks would involve one or more massive dark matter haloes (>1014 M⊙) of the redshift, and the density troughs tend to be empty of massive haloes over >10 comoving Mpc. Besides, the density peaks and troughs at z ≲ 0.6 are in part identified as positive and negative weak lensing signals respectively, in mean tangential shear profiles, showing a good agreement with those inferred from the full-sky weak lensing simulation. The coming extensive spectroscopic surveys will be able to resolve these colossal structures in 3D space. The number density information over the entire survey field is available as grid-point data on the website of the HSC-SSP data release (https://hsc.mtk.nao.ac.jp/ssp/data-release/).
Abstract
We present the demography of the dynamics and gas mass fraction of 33 extremely metal-poor galaxies (EMPGs) with metallicities of 0.015–0.195
Z
⊙
and low stellar masses of 10
4
–10
8
M
⊙
in ...the local universe. We conduct deep optical integral field spectroscopy (IFS) for the low-mass EMPGs with the medium-high resolution (
R
= 7500) grism of the 8 m Subaru FOCAS IFU instrument by the EMPRESS 3D survey, and investigate the H
α
emission of the EMPGs. Exploiting the resolution high enough for the low-mass galaxies, we derive gas dynamics with the H
α
lines by the fitting of three-dimensional disk models. We obtain an average maximum rotation velocity (
v
rot
) of 15 ± 3 km s
−1
and an average intrinsic velocity dispersion (
σ
0
) of 27 ± 10 km s
−1
for 15 spatially resolved EMPGs out of 33 EMPGs, and find that all 15 EMPGs have
v
rot
/
σ
0
< 1 suggesting dispersion-dominated systems. There is a clear decreasing trend of
v
rot
/
σ
0
with the decreasing stellar mass and metallicity. We derive the gas mass fraction (
f
gas
) for all 33 EMPGs, and find no clear dependence on stellar mass and metallicity. These
v
rot
/
σ
0
and
f
gas
trends should be compared with young high-
z
galaxies observed by the forthcoming JWST IFS programs to understand the physical origins of the EMPGs in the local universe.
PDF
