Publications (47) View all
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Article: Subaru Weak-Lensing Survey of Dark Matter Subhalos in Coma Cluster : Subahlo Mass Function and Statistical Properties
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ABSTRACT: We present 4 square degree weak gravitational lensing survey of subhalos in the nearby Coma cluster using Subaru/Suprime-Cam. Thanks to large apparent size of cluster subhalos, we detected in a model-independent way 32 subhalos down to the order of 10^{-3} of the virial mass of the cluster. Weak-lensing mass measurement of shear-selected subhalos allows us to investigate subhalo properties and the correlation between subhalo masses and galaxy luminosities, for the first time. The mean distortion profiles stacked over subhalos show a sharply truncated feature which is well-fitted by Navarro Frenk & White (NFW) mass model with the truncation radius, as expected by the tidal destruction by the main cluster. We also found that subhalo masses, truncation radii and mass-to-light ratios decrease toward the cluster center. The subhalo mass function, dn/d \ln M_{sub}, in the range of two orders of magnitude in mass, is well described by a single power law or a Schechter function. Best-fit power indices of 1.11^{+0.45}_{-0.29} for the former model and 0.94_{-0.29}^{+0.46} for the latter one are in remarkable agreements with slopes of \sim0.9-1.0 predicted by the cold dark matter paradigm. The tangential distortion signals in the radial range of 0.02-2Mpc/h from the cluster center show a complex structure which is well described by a composition of three mass components of subhalos, NFW mass distribution as a smooth component of the main cluster, and lensing model from large scale structure behind the cluster. Although the lensing signals are one order lower than those for clusters at z\sim0.2, the total signal-to-noise ratio, S/N=13.3, is comparable to or higher because a large number of background source galaxies compensate low lensing efficiency of the nearby cluster.04/2013; -
Article: Assembly of Massive Galaxies in a High-z Protocluster
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ABSTRACT: We present the results of wide-field deep JHK imaging of the SSA22 field using MOIRCS instrument equipped with Subaru telescope. The observed field is 112 arcmin^2 in area, which covers the z=3.1 protocluster characterized by the overdensities of Ly Alpha emitters (LAEs) and Ly Alpha Blobs (LABs). The 5 sigma limiting magnitude is K_{AB} = 24.3. We extract the potential protocluster members from the K-selected sample by using the multi-band photometric-redshift selection as well as the simple color cut for distant red galaxies (DRGs; J-K_{AB}>1.4). The surface number density of DRGs in our observed fields shows clear excess compared with those in the blank fields, and the location of the densest area whose projected overdensity is twice the average coincides with the large-scale density peak of LAEs. We also found that K-band counterparts with z_{phot} = 3.1 are detected for 75% (15/20) of the LABs within their Ly Alpha halo, and the 40 % (8/20) of LABs have multiple components, which gives a direct evidence of the hierarchical multiple merging in galaxy formation. The stellar mass ofLABs correlates with their luminosity, isophotal area, and the Ly Alpha velocity widths, implying that the physical scale and the dynamical motion of Ly Alpha emission are closely related to their previous star-formation activities. Highly dust-obscured galaxies such as hyper extremely red objects (HEROs; J-K_{AB}>2.1) and plausible K-band counterparts of submillimeter sources are also populated in the high density region.03/2012; -
Article: Total to central luminosity ratios of quiescent galaxies in MODS as an indicator of size evolution
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ABSTRACT: Using the very deep Subaru images of the GOODS-N region, from the MOIRCS Deep Survey and images from the HST/ACS, we have measured the Luminosity Ratio (LR) of the outer to the central regions of massive (M>10^{10.5}M_{Sun}) galaxies at fixed radii in a single rest-frame for z<3.5 as a new approach to the problem of size evolution. We didn't observe any evolution in the median LR. Had a significant size growth occurred, the outer to central luminosity ratios would have demonstrated a corresponding increase with a decrease in redshift.02/2012; -
Article: A universal stellar-mass and size relation of galaxies in GOODS-N region
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ABSTRACT: We present scaling relations between stellar-mass (Mstar) and the size of galaxies at 0.3 < z < 3 for half- (R_50) and 90 percent-light (R_90) radii, using a deep K-band selected catalogue taken with the Subaru Telescope and MOIRCS in the GOODS-North region. The logarithmic slope R \propto Mstar^{0.1-0.2} is independent of redshift in a wide mass range of Mstar ~ 10^8-10^11 Msun, irrespective of galaxy populations (star-forming, quiescent). The offset change is < 50 percent. Provided that optical light in the rest frame traces the stellar mass of galaxies, the universal relation demonstrates that the stellar mass was built up in galaxies over their cosmic histories in a similar manner on average irrelevant to galaxy mass. The small offset in each stellar mass bin from the universal relation shows weak size evolution at a given mass. There is a moderate increase of 30-50 percent for R_50 and R_90 for less massive galaxies (Mstar < 10^10 Msun) from z~3 to z~1, while the sizes remains unchanged or slightly decrease towards z~0.3. For massive galaxies (Mstar > 10^11 Msun), the evolution is ~70-80 % increase in R_90 from z~3 to z~0.3, though that in R_50 is weaker. The evolution of compactness factor, R_50/R_90, which becomes smaller at lower redshift, is suggestive of minor merging effect in the outer envelope of massive galaxies.02/2012; -
Article: The Role of Galaxy Interaction in Environmental Dependence of the Star Formation Activity at z~1.2
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ABSTRACT: In order to understand environmental effects on star formation in high-redshift galaxies, we investigate the physical relationships between the star formation activity, stellar mass, and environment for z ~1.2 galaxies in the 2 deg^2 COSMOS field. We estimate star formation using the [OII] emission line and environment from the local galaxy density. Our analysis shows that for massive galaxies M_*>10^10 M_sun, the fraction of [OII] emitters in high-density environments is 1.7 times higher than in low-density environments, while the [OII] emitter fraction does not depend on environment for low-mass M_* < 10^10 M_sun galaxies. In order to understand what drives these trends, we investigate the role of companion galaxies in our sample. We find that the fraction of [OII] emitters in galaxies with companions is 2.4 times as high as that in galaxies without companions at M_* > 10^10 M_sun. In addition, massive galaxies are more likely to have companions in high-density environments. However, although the "number" of star forming galaxies increases for massive galaxies with close companions and in dense environments, the "average" star formation rate of star forming galaxies at a given mass is independent of environment and the presence/absence of a close companion. These results suggest that interactions and/or mergers in high-density environment could induce star formation in massive galaxies at z~1.2, increasing the fraction of star-forming galaxies with M_* > 10^10 M_sun.12/2011;
