We report fourteen and twenty-eight protocluster candidates at z = 5.7 and 6.6 over 14 and 19 deg2 areas, respectively, selected from 2,230 Lyα emitters (LAEs) photometrically identified with Subaru/Hyper Suprime-Cam (HSC) deep images. Six out of the 42 protocluster candidates include at least 1 spectroscopically confirmed LAEs at redshifts up to z = 6.574. By the comparisons with the cosmological Lyα radiative transfer (RT) model reproducing LAEs with the reionization effects, we find that more than a half of these protocluster candidates might be progenitors of the present-day clusters with a mass of ≳ 1014M⊙. We also investigate the correlation between LAE overdensity and Lya rest-frame equivalent width (EW), because the cosmological Lyα RT model suggests that a slope of EW-overdensity relation is steepened towards the epoch of cosmic reionization (EoR), due to the existence of the ionized bubbles around galaxy overdensities easing the escape of Lyα emission from the partly neutral intergalactic medium. The available HSC data suggest that the slope of the EW-overdensity correlation does not evolve from the post-reionization epoch z = 5.7 to the EoR z = 6.6 beyond the moderately large statistical errors.

We have carried out a wide and deep imaging survey for the Local Group dwarf spheroidal galaxy Ursa Minor (UMi) using Hyper Suprime-Cam (HSC). The data cover out beyond the nominal tidal radius down to ~25 mag in i band, which is ~2 mag below the main sequence turn-off point. The structural parameters of UMi are derived using red giant branch (RGB) stars and sub-giant branch (SGB) stars, and the tidal radius is suggested to be larger than those estimated by the previous studies. It is also found that the distribution of bluer RGB/SGB stars is more extended than that of redder RGB/SGB stars. The fraction of binary systems is estimated to be ~0.4 from the morphology of the main sequences.

We have carried out an imaging survey for Local Group dwarf spheroidal galaxy Ursa Minor (UMi) using Hyper Suprime-Cam (HSC) on the 8.2m Subaru Telescope. Wide and deep data obtained by HSC enable us to investigate the extent of UMi which is revealed to extend out to twice the nominal tidal radius. The fraction of binary systems is also investigated from the morphology of the main sequence and estimated to be ~0.4.

Local Group galaxies are important targets since their stellar populations can be resolved, and their properties can be investigated in detail with the help of stellar evolutionary models. The newly-built instrument for the 8.2m Subaru Telescope, Hyper Suprime-Cam (HSC), which has a 1 Giga pixel CCD camera with 1.5 degrees field of view, is the best instrument for observing Local Group galaxies. We have carried out a survey for Local Group dwarf galaxies using HSC aiming to shed light on the outskirts of these galaxies. The survey covers target galaxies out beyond the tidal radii down to a depth unexplored by previous surveys. Thanks to the high spatial resolution and high sensitivity provided by the Subaru Telescope, we are able to investigate properties such as spatial distribution and stellar population from the very center of galaxies to the outskirts. In this article, I will show results for the dwarf irregular galaxy NGC 6822 and the dwarf spheroidal galaxy Ursa Minor.

We report on the first results from our pilot observation of nearby galaxies with Hyper Suprime-Cam. We have observed two galaxies with mass similar to that of the Milky Way Galaxy and measured the abundance of their satellite galaxies in order to address the missing satellite problem outside of the Local Group. We find that (1) the abundance of dwarf galaxies is smaller by a factor of two than the prediction from one of the current hydro-dynamical simulations and (2) there is a large halo to halo scatter. Our results highlight the importance of a statistical sample of nearby galaxies to address the missing satellite problem.

We present a progress report on our deep and wide-field imaging survey of the Andromeda halo with Hyper Suprime Cam (HSC) mounted on Subaru. HSC is the upgraded prime focus camera after Suprime-Cam, having a field of view of 1.77 square degree (1.5 degree in diameter), namely about 10 times larger than that of Suprime-Cam. This camera will thus offer us great opportunities to explore unique and legacy surveys for the Andromeda halo, as well as for other Galactic Archaeology science cases.

We have observed on-going interacting galaxies (NGC4631 and NGC4656) using Subaru/Hyper Suprime-Cam and reduced the data using HSC pipeline and conducted photometry based on DAOphot. Then, we have detected 8 new dwarf galaxy candidates in the outer region of NGC4631 and confirmed the three candidates previously reported by Karachentsev et al. 2014. The 3 or 4 candidates detected in this study may be a star-forming dwarf irregular galaxy and the other 7 candidates may be an old dwarf spheroidal galaxy based on these stellar populations. It looks like that the effective radius - absolute magnitude relation of dwarf galaxies in NGC4631 group is similar to the relation of the Local Group and the other galaxy systems.

We report the discovery of a probable large-scale structure composed of many galaxy clumps around the known twin clusters at $z=1.26$ and $z=1.27$ in the Lynx region. Our analysis is based on deep, panoramic, and multi-colour imaging with the Suprime-Cam on the 8.2 m Subaru telescope. We apply a photometric redshift technique to extract plausible cluster members at $z\sim1.27$ down to $\sim M^\ast+2.5$. From the 2-D distribution of these photometrically selected galaxies, we newly identify seven candidates of galaxy groups or clusters where the surface density of red galaxies is significantly high ($>$5$\sigma$), in addition to the two known clusters, comprising the largest most distant supercluster ever identified.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Photometric properties (effective surface brightness, effective radius, radial profile index, axis ratio, color, color gradient) of 328 galaxies in the Coma cluster fainter than $R=15$ mag are examined as a function of the distance from the cluster center. No significant gradient is found for the effective surface brightness, effective radius and radial profile index. The distribution of axis ratios shows a concentration of round galaxies at the cluster center in the magnitude range $16.5 \lt R \lt 18$; most of these are found to be old and to have intermediate metal abundance, suggesting that they are nucleated dwarf ellipticals. On the other hand, we find a significant gradient in color, in the sense that galaxy colours become bluer with increasing distance from the cluster center. We conclude that this color gradient represents a metallicity gradient.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A surprising result of our recent spectroscopic survey of galaxies in the Coma cluster has been the discovery of a possible bimodal distribution in the metallicities of faint galaxies at MB > −17. We identified a group of dwarfs with luminosity-weighted metallicities around solar and a group with [M/H] around −1.5. A metallicity bimodality among galaxies of similar luminosities is unexpected and suggests that faint cluster galaxies could be an heterogeneous population that formed through more than one evolutionary path, possibly as a consequence of the cluster environment.

Fine features of the dust distribution in the central region of NGC 4151 have been studied from high resolution images obtained by the Subaru Telescope. The two dust lanes lying along a circum-nuclear ellipse of 40“ ×20” have been recognized to consist of a number of fine filaments and knots. In the inner region, there has been found dust distributed in a bipolar cone region extending to 5” from the nucleus. This cone is exactly complementary to the well-known bipolar ionized gaseous region. A dense knot is seen at 2” SE from the nucleus, but no torus-like feature is recognized. The masses of neutral gas in the outer lanes and in the inner region are estimated as 106M⊙ and 105M⊙ respectively. These observational results are compared with results of numerical simulations of gas dynamics.