A redshift survey of the Coma Cluster (A1656): understanding the nature of subhalos in the weak-lensing map

We study the physical properties of weak-lensing subhalos in the Coma cluster of galaxies using data from galaxy redshift surveys. The data include 12,989 galaxies with measured spectroscopic redshifts (2184 from our MMT/Hectospec observations and 10,807 from the literature). The r-band magnitude limit at which the differential spectroscopic completeness drops below 50% is 20.2 mag, which is spatially uniform in a region of 4.5 deg² where the weak-lensing map of N. Okabe et al. exists. We identify 1337 member galaxies in this field and use them to understand the nature of 32 subhalos detected in a weak-lensing analysis. We use Gaussian mixture modeling (GMM) in the line-of-sight velocity domain to measure the mean velocity, the velocity dispersion, and the number of subhalo galaxies by mitigating contamination from interloping galaxies. Using subhalo properties calculated with the GMM, we find no significant difference in the redshift space distribution between the cluster member galaxies and subhalos. We find that the weak-lensing mass shows strong correlations with the number of subhalo member galaxies, velocity dispersion, and dynamical mass of subhalos with power-law slopes of 0.54_-0.15^+0.16 , 0.93_-0.32^+0.35 , and 0.50_-0.18^+0.31 , respectively. The slope of the mass-velocity dispersion relation of the weak-lensing subhalos appears shallower than that of galaxy clusters, galaxy groups, and individual galaxies. These results suggest that the combination of redshift surveys with weak-lensing maps can be a powerful tool for better understanding the nature of subhalos in clusters.