330 research outputs found
First results on the cluster galaxy population from the Subaru Hyper Suprime-Cam survey. II. Faint end color-magnitude diagrams and radial profiles of red and blue galaxies at
We present a statistical study of the redshift evolution of the cluster
galaxy population over a wide redshift range from 0.1 to 1.1, using
optically-selected CAMIRA clusters from ~deg of the Hyper
Suprime-Cam (HSC) Wide S16A data. Our stacking technique with a statistical
background subtraction reveals color-magnitude diagrams of red-sequence and
blue cluster galaxies down to faint magnitudes of . We find that
the linear relation of red-sequence galaxies in the color-magnitude diagram
extends down to the faintest magnitudes we explore with a small intrinsic
scatter . The scatter does not evolve significantly
with redshift. The stacked color-magnitude diagrams are used to define red and
blue galaxies in clusters for studying their radial number density profiles
without resorting to photometric redshifts of individual galaxies. We find that
red galaxies are significantly more concentrated toward cluster centers and
blue galaxies dominate the outskirt of clusters. We explore the fraction of red
galaxies in clusters as a function of redshift, and find that the red fraction
decreases with increasing distances from cluster centers. The red fraction
exhibits a moderate decrease with increasing redshift. The radial number
density profiles of cluster member galaxies are also used to infer the location
of the steepest slope in the three dimensional galaxy density profiles. For a
fixed threshold in richness, we find little redshift evolution in this
location.Comment: 18pages, 10 figures, accepted as PASJ special issu
A New Milky Way Satellite Discovered In The Subaru/Hyper Suprime-Cam Survey
We report the discovery of a new ultra-faint dwarf satellite companion of the
Milky Way based on the early survey data from the Hyper Suprime-Cam Subaru
Strategic Program. This new satellite, Virgo I, which is located in the
constellation of Virgo, has been identified as a statistically significant (5.5
sigma) spatial overdensity of star-like objects with a well-defined main
sequence and red giant branch in their color-magnitude diagram. The
significance of this overdensity increases to 10.8 sigma when the relevant
isochrone filter is adopted for the search. Based on the distribution of the
stars around the likely main sequence turn-off at r ~ 24 mag, the distance to
Virgo I is estimated as 87 kpc, and its most likely absolute magnitude
calculated from a Monte Carlo analysis is M_V = -0.8 +/- 0.9 mag. This stellar
system has an extended spatial distribution with a half-light radius of 38
+12/-11 pc, which clearly distinguishes it from a globular cluster with
comparable luminosity. Thus, Virgo I is one of the faintest dwarf satellites
known and is located beyond the reach of the Sloan Digital Sky Survey. This
demonstrates the power of this survey program to identify very faint dwarf
satellites. This discovery of VirgoI is based only on about 100 square degrees
of data, thus a large number of faint dwarf satellites are likely to exist in
the outer halo of the Milky Way.Comment: typos are corrected, 6 pages, 4 figures, accepted for publication in
Ap
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