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Register a new userFirst results on the cluster galaxy population from the Subaru Hyper Suprime-Cam survey. III. Brightest cluster galaxies, stellar mass distribution, and active galaxies
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The unprecedented depth and area surveyed by the Subaru Strategic Program with the Hyper Suprime-Cam (HSC-SSP) have enabled us to construct and publish the largest distant cluster sample out to $zsim 1$ to date. In this exploratory study of cluster galaxy evolution from $z=1$ to $z=0.3$, we investigate the stellar mass assembly history of brightest cluster galaxies (BCGs), evolution of stellar mass and luminosity distributions, stellar mass surface density profile, as well as the population of radio galaxies. Our analysis is the first high redshift application of the top N richest cluster selection, which is shown to allow us to trace the cluster galaxy evolution faithfully. Over the 230 deg$^2$ area of the current HSC-SSP footprint, selecting the top 100 clusters in each of the 4 redshift bins allows us to observe the buildup of galaxy population in descendants of clusters whose $zapprox 1$ mass is about $2times 10^{14},M_odot$. Our stellar mass is derived from a machine-learning algorithm, which is found to be unbiased and accurate with respect to the COSMOS data. We find very mild stellar mass growth in BCGs (about 35% between $z=1$ and 0.3), and no evidence for evolution in both the total stellar mass-cluster mass correlation and the shape of the stellar mass surface density profile. We also present the first measurement of the radio luminosity distribution in clusters out to $zsim 1$, and show hints of changes in the dominant accretion mode powering the cluster radio galaxies at $zsim 0.8$.
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We present the photometric properties of a sample of infrared (IR) bright dust obscured galaxies (DOGs). Combining wide and deep optical images obtained with the Hyper Suprime-Cam (HSC) on the Subaru Telescope and all-sky mid-IR (MIR) images taken with Wide-Field Infrared Survey Explorer (WISE), we discovered 48 DOGs with $i - K_mathrm{s} > 1.2$ and $i - [22] > 7.0$, where $i$, $K_mathrm{s}$, and [22] represent AB magnitude in the $i$-band, $K_mathrm{s}$-band, and 22 $mu$m, respectively, in the GAMA 14hr field ($sim$ 9 deg$^2$). Among these objects, 31 ($sim$ 65 %) show power-law spectral energy distributions (SEDs) in the near-IR (NIR) and MIR regime, while the remainder show a NIR bump in their SEDs. Assuming that the redshift distribution for our DOGs sample is Gaussian, with mean and sigma $z$ = 1.99 $pm$ 0.45, we calculated their total IR luminosity using an empirical relation between 22 $mu$m luminosity and total IR luminosity. The average value of the total IR luminosity is (3.5 $pm$ 1.1) $times$ $10^{13}$ L$_{odot}$, which classifies them as hyper-luminous infrared galaxies (HyLIRGs). We also derived the total IR luminosity function (LF) and IR luminosity density (LD) for a flux-limited subsample of 18 DOGs with 22 $mu$m flux greater than 3.0 mJy and with $i$-band magnitude brighter than 24 AB magnitude. The derived space density for this subsample is log $phi$ = -6.59 $pm$ 0.11 [Mpc$^{-3}$]. The IR LF for DOGs including data obtained from the literature is well fitted by a double-power law. The derived lower limit for the IR LD for our sample is $rho_{mathrm{IR}}$ $sim$ 3.8 $times$ 10$^7$ [L$_{odot}$ Mpc$^{-3}$] and its contributions to the total IR LD, IR LD of all ultra-luminous infrared galaxies (ULIRGs), and that of all DOGs are $>$ 3 %, $>$ 9 %, and $>$ 15 %, respectively.
Using photometric galaxies from the HSC survey, we measure the stellar mass density profiles for satellite galaxies as a function of the projected distance, $r_p$, to isolated central galaxies (ICGs) selected from SDSS/DR7 spectroscopic galaxies at $zsim0.1$. By stacking HSC images, we also measure the projected stellar mass density profiles for ICGs and their stellar halos. The total mass distributions are further measured from HSC weak lensing signals. ICGs dominate within $sim$0.15 times the halo virial radius ($0.15R_{200}$). The stellar mass versus total mass fractions drop with the increase in $r_p$ up to $sim0.15R_{200}$, beyond which they are less than 1% while stay almost constant, indicating the radial distribution of satellites trace dark matter. The total stellar mass in satellites is proportional to the virial mass of the host halo, $M_{200}$, for ICGs more massive than $10^{10.5}M_odot$, i.e., $M_{ast,mathrm{sat}} propto M_{200}$, whereas the relation between the stellar mass of ICGs $+$ stellar halos and $M_{200}$ is close to $M_{ast,mathrm{ICG+diffuse}}propto M_{200}^{1/2}$. Below $10^{10.5}M_odot$, the change in $M_{200}$ is much slower with the decrease in $M_{ast,mathrm{ICG+diffuse}}$. At fixed stellar mass, red ICGs are hosted by more massive dark matter halos and have more satellites. At $M_{200}sim10^{12.7}M_odot$, both $M_{ast,mathrm{sat}}$ and the fraction of stellar mass in satellites versus total stellar mass, $f_mathrm{sat}$, tend to be slightly higher around blue ICGs, perhaps implying the late formation of blue galaxies. $f_mathrm{sat}$ increases with the increase in both $M_{ast,mathrm{ICG+diffuse}}$ and $M_{200}$, and scales more linearly with $M_{200}$. We provide best-fitting formulas for these scaling relations and for red and blue ICGs separately.
We present the first results of the Subaru/Hyper Suprime-Cam (HSC) survey of the interacting galaxy system, NGC4631 and NGC4656. From the maps of resolved stellar populations, we identify 11 dwarf galaxies (including already-known dwarfs) in the outer region of NGC4631 and the two tidal stellar streams around NGC4631, named Stream SE and Stream NW, respectively. This paper describes the fundamental properties of these tidal streams. Based on the tip of red giant branch method and the Bayesian statistics, we find that StreamSE (7.10 Mpc in Expected a posteriori, EAP, with the 90% credible intervals of [6.22, 7.29] Mpc) and StreamNW (7.91 Mpc in EAP with the 90% credible intervals of [6.44, 7.97] Mpc) are located in front of and behind NGC4631, respectively. We also calculate the metallicity distribution of stellar streams by comparing the member stars with theoretical isochrones on the color-magnitude diagram. We find that both streams have the same stellar population based on the Bayesian model selection method, suggesting that they originated from a tidal interaction between NGC4631 and a single dwarf satellite. The expected progenitor has a positively skewed metallicity distribution function with [M/H]_EAP=-0.92 with the 90% credible intervals of [-1.46, -0.51]. The stellar mass of the progenitor is estimated as 3.7 x 10e+8 Msun with the 90% credible intervals of [5.8 x 10e+6, 8.6 x 10e+9] Msun based on the mass-metallicity relation for Local group dwarf galaxies. This is in good agreement with an initial stellar mass of the progenitor presumed in the previous N-body simulation.
We present a photometric survey of the stellar halo of the Andromeda galaxy, using Suprime-Cam on the Subaru Telescope. A detailed analysis of VI color-magnitude diagrams of the resolved stellar population is used to measure properties such as line-of-sight distance, surface brightness, metallicity, and age, and these are used to isolate and characterize different components of the M31 halo: (1) several substructures, and (2) the smooth halo. First, we study M31s halo substructure along the north-west/south-east minor axis out to R ~ 100 kpc and the south-west major axis region at R ~ 60 kpc. We confirm two substructures in the south-east halo reported by Ibata et al. (2007) and discover two overdense substructures in the north-west halo. We investigate the properties of these four substructures as well as other structures including the western shelf and find that differences in stellar populations among these systems, thereby suggesting each has a different origin. Our statistical analysis implies that the M31 halo as a whole may contain at least 16 substructures, each with a different origin. Second, we investigate the properties of an underlying, smooth and extended halo component out to R > 100 kpc. We find that the surface density of this smooth halo can be fitted to a Hernquist model of scale radius ~ 17 kpc or a power-law profile with ~ R^{-2.17 +/- 0.15}. In contrast to the relative smoothness of the halo density profile, its metallicity distribution appears to be spatially non-uniform with non-monotonic variations with radius, suggesting that the halo population has not had sufficient time to dynamically homogenize the accreted populations. Further implications for the formation of the M31 halo are discussed.
As part of our survey of galactic stellar halos, we investigate the structure and stellar populations of the northern outer part of the stellar halo in NGC55, a member galaxy of the Sculptor Group, using deep and wide-field V- and I-band images taken with Subaru/Suprime-Cam. Based on the analysis of the color-magnitude diagrams (CMDs) for red-giant-branch (RGB) stars, we derive a tip of RGB (TRGB)-based distance modulus to the galaxy of (m-M)_0 = 26.58 +/- 0.11 (d = 2.1 +/- 0.1 Mpc). From the stellar density maps, we detect the asymmetrically disturbed, thick disk structure and two metal-poor overdense substructures in the north region of NGC55, which may correspond to merger remnants associated with hierarchical formation of NGC55s halo. In addition, we identify a diffuse metal-poor halo extended out to at least z ~ 16 kpc from the galactic plane. The surface-brightness profiles toward the z-direction perpendicular to the galactic plane suggest that the stellar density distribution in the northern outer part of NGC55 is described by a locally isothermal disk at z <~ 6 kpc and a likely diffuse metal-poor halo with V-band surface brightness of mu_V >~ 32 mag arcsec^{-2}, where old RGB stars dominate. We derive the metallicity distributions (MDs) of these structures on the basis of the photometric comparison of RGB stars with the theoretical stellar evolutionary models. The MDs of the thick disk structures show the peak and mean metallicity of [Fe/H]peak ~ -1.4 and [Fe/H]mean ~ -1.7, respectively, while the outer substructures show more metal-poor features than the thick disk structure. Combined with the current results with our previous study for M31s halo, we discuss the possible difference in the formation process of stellar halos among different Hubble types.
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