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
A proto-cluster core is the most massive dark matter halo (DMH) in a given proto-cluster. To reveal the galaxy formation in core regions, we search for proto-cluster cores at z ∼ 2 in ...${\sim}1.5\, \mathrm{deg}^{2}$ of the COSMOS field. Using pairs of massive galaxies log (M*/M⊙) ≥ 11 as tracers of cores, we find 75 candidate cores, among which 54 per cent are estimated to be real. A clustering analysis finds that these cores have an average DMH mass of $2.6_{-0.8}^{+0.9}\times 10^{13}\, \mathrm{M}_{\odot }$, or $4.0_{-1.5}^{+1.8}\, \times 10^{13} \, \mathrm{M}_{\odot }$ after contamination correction. The extended Press–Schechter model shows that their descendant mass at z = 0 is consistent with Fornax-like or Virgo-like clusters. Moreover, using the IllustrisTNG simulation, we confirm that pairs of massive galaxies are good tracers of DMHs massive enough to be regarded as proto-cluster cores. We then derive the stellar mass function (SMF) and the quiescent fraction for member galaxies of the 75 candidate cores. We find that the core galaxies have a more top-heavy SMF than field galaxies at the same redshift, showing an excess at log (M*/M⊙) ≳ 10.5. The quiescent fraction, $0.17_{-0.04}^{+0.04}$ in the mass range 9.0 ≤ log (M*/M⊙) ≤ 11.0, is about three times higher than that of field counterparts, giving an environmental quenching efficiency of $0.13_{-0.04}^{+0.04}$. These results suggest that stellar mass assembly and quenching are accelerated as early as z ∼ 2 in proto-cluster cores.
Abstract
We report a
z
= 2.30 galaxy protocluster (COSTCO-I) in the COSMOS field, where the Ly
α
forest as seen in the CLAMATO IGM tomography survey does not show significant absorption. This departs ...from the transmission–density relationship (often dubbed the fluctuating Gunn–Peterson approximation; FGPA) usually expected to hold at this epoch, which would lead one to predict strong Ly
α
absorption at the overdensity. For comparison, we generate mock Ly
α
forest maps by applying the FGPA to constrained simulations of the COSMOS density field and create mocks that incorporate the effects of finite sight-line sampling, pixel noise, and Wiener filtering. Averaged over
r
= 15
h
−1
Mpc around the protocluster, the observed Ly
α
forest is consistently more transparent in the real data than in the mocks, indicating a rejection of the null hypothesis that the gas in COSTCO-I follows the FGPA (
p
= 0.0026, or 2.79
σ
significance). It suggests that the large-scale gas associated with COSTCO-I is being heated above the expectations of the FGPA, which might be due to either large-scale AGN jet feedback or early gravitational shock heating. COSTCO-I is the first known large-scale region of the IGM that is observed to be transitioning from the optically thin photoionized regime at cosmic noon to eventually coalesce into an intracluster medium (ICM) by
z
= 0. Future observations of similar structures will shed light on the growth of the ICM and allow constraints on AGN feedback mechanisms.
We have conducted interferometric observations with the Combined Array for Research in Millimeter Astronomy (CARMA) and an on-the-fly mapping with the 45 m telescope at Nobeyama Radio Observatory ...(NRO45) in the CO (J = 1-0) emission line of the nearby spiral galaxy NGC 3521. Using the new combined CARMA + NRO45 data of NGC 3521, together with similar data for NGC 5194 (M51a) and archival SINGS H Delta *a, 24 Delta *mm THINGS H I, and Galaxy Evolution Explorer/Far-UV (FUV) data for these two galaxies, we investigate the empirical scaling law that connects the surface density of star formation rate (SFR) and cold gas (known as the Schmidt-Kennicutt law or S-K law) on a spatially resolved basis and find a super-linear slope for the S-K law when carefully subtracting the background emissions in the SFR image. We argue that plausibly deriving SFR maps of nearby galaxies requires the diffuse stellar and dust background emission to be subtracted carefully (especially in the mid-infrared and to a lesser extent in the FUV). Applying this approach, we perform a pixel-by-pixel analysis on both galaxies and quantitatively show that the controversial result whether the molecular S-K law (expressed as ) is super-linear or basically linear is a result of removing or preserving the local background. In both galaxies, the power index of the molecular S-K law is super-linear () at the highest available resolution (~230 pc) and decreases monotonically for decreasing resolution. We also find in both galaxies that the scatter of the molecular S-K law () monotonically increases as the resolution becomes higher, indicating a trend for which the S-K law breaks down below some scale. Both and are systematically larger in M51a than in NGC 3521, but when plotted against the de-projected scale ( Delta *ddp), both quantities become highly consistent for the two galaxies, tentatively suggesting that the sub-kpc molecular S-K law in spiral galaxies depends only on the scale being considered, without varying among spiral galaxies. A logarithmic function and a linear relation are obtained through fitting to the M51a data, which describes both galaxies impressively well on sub-kpc scales. A larger sample of galaxies with better sensitivity, resolution, and broader field of view are required to test the general applicability of these relations.
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
Star-forming galaxies display a close relation among stellar mass, metallicity, and star formation rate (or molecular-gas mass). This is known as the fundamental metallicity relation (FMR) ...(or molecular-gas FMR), and it has a profound implication on models of galaxy evolution. However, there still remains a significant residual scatter around the FMR. We show here that a fourth parameter, the surface density of stellar mass, reduces the dispersion around the molecular-gas FMR. In a principal component analysis of 29 physical parameters of 41 338 star-forming galaxies, the surface density of stellar mass is found to be the fourth most important parameter. The new 4D fundamental relation forms a tighter hypersurface that reduces the metallicity dispersion to 50 per cent of that of the molecular-gas FMR. We suggest that future analyses and models of galaxy evolution should consider the FMR in a 4D space that includes surface density. The dilution time-scale of gas inflow and the star-formation efficiency could explain the observational dependence on surface density of stellar mass.
Abstract
We present UV and Ly
α
radial surface brightness (SB) profiles of Ly
α
emitters (LAEs) at
z
= 2.84 detected with the Hyper Suprime-Cam on the Subaru Telescope. The depth of our data, ...together with the wide-field coverage including a protocluster, enable us to study the dependence of Ly
α
halos (LAHs) on various galaxy properties, including Mpc scale environments. UV and Ly
α
images of 3490 LAEs are extracted, and stacking the images yields SB sensitivity of
∼
1
×
10
−
20
erg
s
−
1
cm
−
2
arcsec
−
2
in Ly
α
, reaching the expected level of optically thick gas illuminated by the UV background at
z
∼ 3. Fitting of the two-component exponential function gives the scale-lengths of 1.56 ± 0.01 and 10.4 ± 0.3 pkpc. Dividing the sample according to their photometric properties, we find that, while the dependence of halo scale-length on environment outside of the protocluster core is not clear, LAEs in the central regions of protoclusters appear to have very large LAHs, which could be caused by combined effects of source overlapping and diffuse Ly
α
emission from cool intergalactic gas permeating the forming protocluster core irradiated by active members. For the first time, we identify
UV halos
around bright LAEs that are probably due to a few lower-mass satellite galaxies. Through comparison with recent numerical simulations, we conclude that, while scattered Ly
α
photons from the host galaxies are dominant, star formation in satellites evidently contributes to LAHs, and that fluorescent Ly
α
emission may be boosted within protocluster cores at cosmic noon and/or near bright QSOs.
ABSTRACT
We present a five-broad-band (grizy) photometric catalogue of Subaru/Hyper Suprime-Cam (HSC) optical imaging observations at around the North Ecliptic Pole (NEP) where the AKARI infrared ...(IR) satellite conducted a large survey (NEP-Wide survey). The observations cover almost all the NEP-Wide survey field down to the depth of 28.1, 26.8, 26.3, 25.5, and 25.0 mag (5σ) at grizy, respectively. The five-band HSC catalogue contains about 2.6 million objects, and 70 959 AKARI NEP-Wide counterpart sources are identified in the catalogue. We added existing supplementary catalogues from the u band to the far-IR band, and estimated photo-z for the AKARI-HSC sources. We achieved σΔz/(1 + zs) = 0.06 and an outlier rate of 13.4 per cent at z = 0.2–1.5. Using the spectral energy distribution (SED) template fitting, we classified the AKARI-HSC galaxies into four categories, namely quiescent, star-forming, Type1 active galactic nucleus (AGN), and Type2 AGN, in each redshift bin. At z > 1, the mean SED of star-forming galaxies in mid-IR (3–10 μm) range is significantly different from that of spiral galaxies in the nearby Universe, indicating that many of star-forming galaxies at z > 1 contain a heat source capable of heating dust to temperatures that radiate thermal emission in the mid-IR range. Furthermore, we estimated the number fraction of AGNs (fAGN) in each bin of redshift and IR luminosity (LIR), and examined the dependence of redshift and LIR. In log(LIR/L⊙) = 11.0–14.0, the fAGN shows a significant increase with increasing redshift, regardless of the LIR bins. In contrast, the fAGN shows a slight increase against LIR at z < 1 and no increase with increasing LIR at z > 1.
We resolve 182 individual giant molecular clouds (GMCs) larger than 2.5 x 10 super(5) M sub(middot in circle) in the inner disks of 5 large nearby spiral galaxies (NGC 2403, NGC 3031, NGC 4736, NGC ...4826, and NGC 6946) to create the largest such sample of extragalactic GMCs within galaxies analogous to the Milky Way. Using a conservatively chosen sample of GMCs most likely to adhere to the virial assumption, we measure cloud sizes, velocity dispersions, and super(12)CO (J = 1-0) luminosities and calculate cloud virial masses. The average conversion factor from CO flux to H sub(2) mass (or X sub(CO)) for each galaxy is 1-2 x 10 super(20) cm super(-2) (K km s super(-1)) super(-1), all within a factor of two of the Milky Way disk value (~2 x 10 super(20) cm super(-2) (K km s super(-1)) super(-1)). We find GMCs to be generally consistent within our errors between the galaxies and with Milky Way disk GMCs; the intrinsic scatter between clouds is of order a factor of two. Consistent with previous studies in the Local Group, we find a linear relationship between cloud virial mass and CO luminosity, supporting the assumption that the clouds in this GMC sample are gravitationally bound. We do not detect a significant population of GMCs with elevated velocity dispersions for their sizes, as has been detected in the Galactic center. Though the range of metallicities probed in this study is narrow, the average conversion factors of these galaxies will serve to anchor the high metallicity end of metallicity-X sub(CO) trends measured using conversion factors in resolved clouds; this has been previously possible primarily with Milky Way measurements.
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