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.
Abstract
We construct a new catalog of extragalactic X-ray binaries (XRBs) by matching the latest Chandra source catalog with local galaxy catalogs. Our XRB catalog contains 4430 XRBs hosted by 237 ...galaxies within ∼130 Mpc. As XRBs dominate the X-ray activity in galaxies, the catalog enables us to study the correlations between the total X-ray luminosity of a galaxy LX,tot, star formation rate $\dot{\rho }_\star$, and stellar mass M⋆. As previously reported, LX,tot is correlated with $\dot{\rho }_\star$ and M⋆. In particular, we find that there is a fundamental plane in those three parameters; $\log L_{\rm X,tot}={38.80^{+0.09}_{-0.12}}+\log (\dot{\rho }_\star + \alpha M_\star )$, where α = (3.36 ± 1.40) × 10−11 yr−1. In order to investigate this relation, we construct a phenomenological binary population synthesis model. We find that the high-mass XRB and low-mass XRB fraction in formed compact object binary systems is $\sim\! 9\%$ and ${0.04}\%$, respectively. Utilizing the latest XMM-Newton and Swift X-ray source catalog data sets, additional XRB candidates are also found, resulting in a total of 5757 XRBs hosted by 311 galaxies.
We measure the redshift-space correlation function from a spectroscopic sample of 2783 emission line galaxies from the FastSound survey. The survey, which uses the Subaru Telescope and covers a ...redshift range of 1.19 < z < 1.55, is the first cosmological study at such high redshifts. We detect clear anisotropy due to redshift-space distortions (RSD) both in the correlation function as a function of separations parallel and perpendicular to the line of sight and its quadrupole moment. RSD has been extensively used to test general relativity on cosmological scales at z < 1. Adopting a ΛCDM cosmology with the fixed expansion history and no velocity dispersion (σv = 0), and using the RSD measurements on scales above 8 h−1 Mpc, we obtain the first constraint on the growth rate at the redshift, f (z)σ8(z) = 0.482 ± 0.116 at z ∼ 1.4 after marginalizing over the galaxy bias parameter b(z)σ8(z). This corresponds to 4.2 σ detection of RSD. Our constraint is consistent with the prediction of general relativity fσ8 ∼ 0.392 within the 1 σ confidence level. When we allow σv to vary and marginalize over it, the growth rate constraint becomes $f\sigma _8=0.494^{+0.126}_{-0.120}$. We also demonstrate that by combining with the low-z constraints on fσ8, high-z galaxy surveys like the FastSound can be useful to distinguish modified gravity models without relying on CMB anisotropy experiments.
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 report on the spectroscopic confirmation of a massive quiescent galaxy at z spec = 4.53 in the COSMOS field. The object was first identified as a galaxy with suppressed star formation at ...z phot ∼ 4.65 from the COSMOS2020 catalog. The follow-up spectroscopy with Keck/MOSFIRE in the K band reveals faint O ii emission and the Balmer break, indicative of evolved stellar populations. We fit the spectral energy distribution using photometry and a spectrum to infer physical properties. The obtained stellar mass is high ( M * ∼ 10 10.8 M ⊙ ) and the current star formation rate is more than 1 dex below that of main-sequence galaxies at z = 4.5. Its star formation history suggests that this galaxy experienced rapid quenching from z ∼ 5. The galaxy is among the youngest quiescent galaxies confirmed so far at z spec > 3 with z form ∼ 5.2 (200 Myr ago), which is the epoch when 50% of the total stellar mass was formed. A unique aspect of the galaxy is that it is in an extremely dense region; there are four massive star-forming galaxies at 4.4 < z phot < 4.7 located within 150 physical kpc from the galaxy. Interestingly, three of them have virial radii that strongly overlap with that of the central quiescent galaxy (∼70 kpc), suggesting that the overdensity region is likely the highest-redshift candidate of a dense group with a spectroscopically confirmed quiescent galaxy at the center. The group provides us with a unique opportunity to gain insights into the role of the group environment in quenching at z ∼ 5, which corresponds to the formation epoch of massive elliptical galaxies in the local Universe.
Abstract
Intrinsic alignments (IA), the coherent alignment of intrinsic galaxy orientations, can be a source of a systematic error of weak lensing surveys. The redshift evolution of IA also contains ...information about the physics of galaxy formation and evolution. This paper presents the first measurement of IA at high redshift, z ∼ 1.4, using the spectroscopic catalog of blue star-forming galaxies of the FastSound redshift survey, with the galaxy shape information from the Canada–Hawaii–France telescope lensing survey. The IA signal is consistent with zero with power-law amplitudes fitted to the projected correlation functions for density–shape and shape–shape correlation components, Aδ+ = −0.0071 ± 0.1340 and A++ = −0.0505 ± 0.0848, respectively. These results are consistent with those obtained from blue galaxies at lower redshifts (e.g., $A\,_{\delta +}=0.0035_{-0.0389}^{+0.0387}$ and $A_{++}=0.0045_{-0.0168}^{+0.0166}$ at z = 0.51 from the WiggleZ survey). The upper limit of the constrained IA amplitude corresponds to a few percent contamination to the weak-lensing shear power spectrum, resulting in systematic uncertainties on the cosmological parameter estimations by −0.052 < Δσ8 < 0.039 and −0.039 < ΔΩm < 0.030.
We study the statistical intrinsic shape of star-forming BzK galaxies (sBzK galaxies) at z ~ 2 in both rest-frame UV and rest-frame optical wavelengths. Of all 1028 galaxies in GOODS-S, 57% (583) ...show a single component in the Advanced Camera for Surveys/F850LP image. As Wide Field Camera (WFC3)/F160W images cover only part of GOODS-S and SXDS, 724/1028 and 2500/29835 sBzK galaxies in GOODS-S and SXDS, respectively, have WFC3 coverage. Of the sBzK galaxies in the WFC3/F160W images, 86% (626) and 82% (2044) appear as a single component in the GOODS-S and SXDS, respectively. A larger fraction of single-component objects in the F850LP images represents multiple star-forming regions in galaxies, while they are not so obvious in the F160W image which appears smoother. Most of the single-component sBzK galaxies show Sersic indices of n = 0.5-2.5, in agreement with those of local disk galaxies.
We present the results from a large near-infrared spectroscopic survey made with Subaru/FMOS (FastSound) consisting of ∼ 4000 galaxies at z ∼ 1.4 with significant Hα detection. We measure the ...gas-phase metallicity from the N iiλ6583/Hα emission line ratio of the composite spectra in various stellar mass and star-formation rate bins. The resulting mass–metallicity relation generally agrees with previous studies obtained in a similar redshift range to that of our sample. No clear dependence of the mass–metallicity relation on star-formation rate is found. Our result at z ∼ 1.4 is roughly in agreement with the fundamental metallicity relation at z ∼ 0.1 with a fiber aperture corrected star-formation rate. We detect significant S iiλλ6716,6731 emission lines from the composite spectra. The electron density estimated from the S iiλλ6716,6731 line ratio ranges from 10–500 cm−3, which generally agrees with that of local galaxies. On the other hand, the distribution of our sample on N iiλ6583/Hα vs. S iiλλ6716,6731/Hα is different to that found locally. We estimate the nitrogen-to-oxygen abundance ratio (N/O) from the N2S2 index, and find that the N/O in galaxies at z ∼ 1.4 is significantly higher than the local values at a fixed metallicity and stellar mass. The metallicity at z ∼ 1.4 recalculated with this N/O enhancement taken into account decreases by 0.1–0.2 dex. The resulting metallicity is lower than the local fundamental metallicity relation.
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.
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