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Register a new userThe stellar halo of isolated central galaxies in the Hyper Suprime-Cam imaging survey
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We study the faint stellar halo of isolated central galaxies, by stacking galaxy images in the HSC survey and accounting for the residual sky background sampled with random points. The surface brightness profiles in HSC $r$-band are measured for a wide range of galaxy stellar masses ($9.2<log_{10}M_ast/M_odot<11.4$) and out to 120 kpc. Failing to account for the stellar halo below the noise level of individual images will lead to underestimates of the total luminosity by $leq 15%$. Splitting galaxies according to the concentration parameter of their light distributions, we find that the surface brightness profiles of low concentration galaxies drop faster between 20 and 100 kpc than those of high concentration galaxies. Albeit the large galaxy-to-galaxy scatter, we find a strong self-similarity of the stellar halo profiles. They show unified forms once the projected distance is scaled by the halo virial radius. The colour of galaxies is redder in the centre and bluer outside, with high concentration galaxies having redder and more flattened colour profiles. There are indications of a colour minimum, beyond which the colour of the outer stellar halo turns red again. This colour minimum, however, is very sensitive to the completeness in masking satellite galaxies. We also examine the effect of the extended PSF in the measurement of the stellar halo, which is particularly important for low mass or low concentration galaxies. The PSF-corrected surface brightness profile can be measured down to $sim$31 $mathrm{mag}/mathrm{arcsec}^2$ at 3-$sigma$ significance. PSF also slightly flattens the measured colour profiles.
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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 a catalog of extended low-surface-brightness galaxies (LSBGs) identified in the Wide layer of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). Using the first ${sim}$200 deg$^2$ of the survey, we have uncovered 781 LSBGs, spanning red ($g-igeq0.64$) and blue ($g-i<0.64$) colors and a wide range of morphologies. Since we focus on extended galaxies ($r_mathrm{eff}=2.5$-$14^{primeprime}$), our sample is likely dominated by low-redshift objects. We define LSBGs to have mean surface brightnesses $bar{mu}_mathrm{eff}(g)>24.3$ mag arcsec$^{-2}$, which allows nucleated galaxies into our sample. As a result, the central surface brightness distribution spans a wide range of $mu_0(g)=18$-$27.4$ mag arcsec$^{-2}$, with 50% and 95% of galaxies fainter than 24.3 and 22 mag arcsec$^{-2}$, respectively. Furthermore, the surface brightness distribution is a strong function of color, with the red distribution being much broader and generally fainter than that of the blue LSBGs, and this trend shows a clear correlation with galaxy morphology. Red LSBGs typically have smooth light profiles that are well-characterized by single-component S{e}rsic functions. In contrast, blue LSBGs tend to have irregular morphologies and show evidence for ongoing star formation. We crossmatch our sample with existing optical, HI, and ultraviolet catalogs to gain insight into the physical nature of the LSBGs. We find that our sample is diverse, ranging from dwarf spheroidals and ultra-diffuse galaxies in nearby groups to gas-rich irregulars to giant LSB spirals, demonstrating the potential of the HSC-SSP to provide a truly unprecedented view of the LSBG population.
We report on the global structure of the Milky Way (MW) stellar halo up to its outer boundary based on the analysis of blue-horizontal branch stars (BHBs). These halo tracers are extracted from the $(g,r,i,z)$ band multi-photometry in the internal data release of the on-going Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) surveyed over $sim550$~deg$^2$ area. In order to select most likely BHBs by removing blue straggler stars (BSs) and other contamination in a statistically significant manner, we have developed and applied an extensive Bayesian method, instead of the simple color cuts adopted in our previous work, where each of the template BHBs and non-BHBs obtained from the available catalogs is represented as a mixture of multiple Gaussian distributions in the color-color diagrams. We found from the candidate BHBs in the range of 18.5<g<23.5 mag that the radial density distribution over a Galactocentric radius of r=36-360 kpc can be approximated as a single power-law profile with an index of $alpha=3.74^{+0.21}_{-0.22}$ or a broken power-law profile with an index of $alpha_{rm in}=2.92^{+0.33}_{-0.33}$ at $r$ below a broken radius of $r_{rm b}=160^{+18}_{-19}$~kpc and a very steep slope of $alpha_{rm out}=15.0^{+3.7}_{-4.5}$ at $r>r_{rm b}$. The latter profile with a prolate shape having an axial ratio of $q=1.72^{+0.44}_{-0.28}$ is most likely and this halo may hold a rather sharp boundary at r=160kpc. The slopes of the halo density profiles are compared with those from the suite of hydrodynamical simulations for the formation of stellar halos. This comparison suggests that the MW stellar halo may consist of the two overlapping components: the in situ. inner halo as probed by RR Lyrae stars showing a relatively steep radial density profile and the ex situ. outer halo with a shallow profile probed by BHBs here, which is made by accretion of small stellar systems.
We perform a consistent comparison of the mass and mass profiles of massive ($M_star > 10^{11.4}M_{odot}$) central galaxies at z~0.4 from deep Hyper Suprime-Cam (HSC) observations and from the Illustris, TNG100, and Ponos simulations. Weak lensing measurements from HSC enable measurements at fixed halo mass and provide constraints on the strength and impact of feedback at different halo mass scales. We compare the stellar mass function (SMF) and the Stellar-to-Halo Mass Relation (SHMR) at various radii and show that the radius at which the comparison is performed is important. In general, Illustris and TNG100 display steeper values of $alpha$ where $M_{star}propto M_{rm vir}^{alpha}$. These differences are more pronounced for Illustris than for TNG100 and in the inner rather than outer regions of galaxies. Differences in the inner regions may suggest that TNG100 is too efficient at quenching in-situ star formation at $M_{rm vir}simeq10^{13} M_{odot}$ but not efficient enough at $M_{rm vir}simeq10^{14} M_{odot}$. The outer stellar masses are in excellent agreement with our observations at $M_{rm vir}simeq10^{13} M_{odot}$, but both Illustris and TNG100 display excess outer mass as $M_{rm vir}simeq10^{14} M_{odot}$ (by ~0.25 and ~0.12 dex, respectively). We argue that reducing stellar growth at early times in $M_star sim 10^{9-10} M_{odot}$ galaxies would help to prevent excess ex-situ growth at this mass scale. The Ponos simulations do not implement AGN feedback and display an excess mass of ~0.5 dex at $r<30$ kpc compared to HSC which is indicative of over-cooling and excess star formation in the central regions. Joint comparisons between weak lensing and galaxy stellar profiles are a direct test of whether simulations build and deposit galaxy mass in the correct dark matter halos and thereby provide powerful constraints on the physics of feedback and galaxy growth.
We present an overview of a deep transient survey of the COSMOS field with the Subaru Hyper Suprime-Cam (HSC). The survey was performed for the 1.77 deg$^2$ ultra-deep layer and 5.78 deg$^2$ deep layer in the Subaru Strategic Program over 6- and 4-month periods from 2016 to 2017, respectively. The ultra-deep layer shows a median depth per epoch of 26.4, 26.3, 26.0, 25.6, and 24.6 mag in $g$, $r$, $i$, $z$, and $y$ bands, respectively; the deep layer is $sim0.6$ mag shallower. In total, 1,824 supernova candidates were identified. Based on light curve fitting and derived light curve shape parameter, we classified 433 objects as Type Ia supernovae (SNe); among these candidates, 129 objects have spectroscopic or COSMOS2015 photometric redshifts and 58 objects are located at $z > 1$. Our unique dataset doubles the number of Type Ia SNe at $z > 1$ and enables various time-domain analyses of Type II SNe, high redshift superluminous SNe, variable stars, and active galactic nuclei.
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