The HectoMAP Cluster Survey - I. redMaPPer Clusters

We use the dense HectoMAP redshift survey to explore the properties of 104 redMaPPer cluster candidates. The redMaPPer systems in HectoMAP cover the full range of richness and redshift (0.08 $< z <$ 0.60). Fifteen systems included in the Subaru/Hyper Suprime-Cam public data release are bona fide clusters. The median number of spectroscopic members per cluster is $\sim20$. We include redshifts of 3547 member candidates listed in the redMaPPer catalog whether they are cluster members or not. We evaluate the redMaPPer membership probability spectroscopically. The scaled richness ({\lambda}rich/S) provided by redMaPPer correlates tightly with the spectroscopic richness regardless of the cluster redshift and appears to be a better mass proxy than the original richness, {\lambda}rich. The purity (number of real systems) in redMaPPer exceeds 90% even at the lowest richness; however, there is some incompleteness. Five massive galaxy clusters (M $\gtrsim 2 \times 10^{13}$ M$_{\odot}$) associated with X-ray emission in the HectoMAP region are missing from the catalog.Comment: submitted to ApJ, a revised version in response to the referee's comments, 15 pages, 14 figures, 3 tables; data will be available when the paper is accepte

Size and Spectroscopic Evolution of HectoMAP Quiescent Galaxies

The HectoMAP survey provides a complete, mass-limited sample of 30,231 quiescent galaxies with $i-$band Hyper Suprime-Cam Subaru Strategic Program (HSC SSP) imaging that spans the redshift range $0.2 <z < 0.6$. We combine half-light radii based on HSC SSP imaging with redshifts and D$_n4000$ to explore the size - mass relation, $R_{e} = A \times M_{*}^{\alpha}$, and its evolution for the entire HectoMAP quiescent population and for two subsets of the data. Newcomers with $1.5 < \mathrm{D}_n4000 < 1.6$ at each redshift show a steeper increase in $A$ as the universe ages than the population that descends from galaxies that are already quiescent at the survey limit, $z \sim 0.6$ (the resident population). In broad agreement with previous studies, evolution in the size - mass relation both for the entire HectoMAP sample and for the resident population (but not for the newcomers alone) is consistent with minor merger driven growth. For the resident population, the evolution in the size - mass relation is independent of the population age at $z \sim 0.6$. The contrast between the sample of newcomers and the resident population provides insight into the role of commonly termed "progenitor bias" on the evolution of the size - mass relation.Comment: 25 pages, 13 figures, submitted to the Astrophysical Journal. Comments are welcome

A Gunn-Peterson test with a QSO at z=6.4

Understanding the cosmic re-ionization is one of the key goals of the modern observational cosmology. High redshift QSO spectra can be used as background light sources to measure absorption by intervening neutral hydrogen. We investigate neutral hydrogen absorption in a deep, moderate-resolution Keck/Deimos spectrum of QSO CFHQSJ2329-0301 at z=6.4. This QSO is one of the highest redshift QSOs presently known at z=6.4 but is 2.5 mag fainter than a previously well-studied QSO SDSSJ1148+5251 at z=6.4. Therefore, it has a smaller Stromgren sphere, and allows us to probe the highest redshift hydrogen absorption to date. The average transmitted flux at 5.915<z_abs<6.365 (200 comoving Mpc) is consistent with zero, in Ly_alpha, Ly_beta, and Ly_gamma absorption measurements. This corresponds to the lower limit of optical depth, tau_eff>4.9. These results are consistent with strong evolution of the optical depth at z>5.7.Comment: 5 pages, 4 figures. Accepted for publication in MNRA