REVISITING THE FOSSIL GROUP CANDIDATES UGC 842 AND NGC 6034

摘要

We present a new insight on NGC 6034 and UGC 842, two groups of galaxies previously reported in the literatureas being fossil groups. The study is based on optical photometry and spectroscopy obtained with the CTIOBlanco telescope and Sloan Digital Sky Survey archival data. We find that NGC 6034 is embedded in a largestructure, dominated by three rich clusters and other small groups. Its first and next four ranked galaxies havemagnitude differences in the r band and projected distances which violate the optical criteria to classify it as afossil group. We confirm that the UGC 842 group is a fossil group, but with about half the velocity dispersionthat is reported in previous works. The velocity distribution of its galaxies reveals the existence of two structuresin its line of sight, one with σ_v~ 223 km s~(-1)and another with σ_v~ 235 km s~(-1),with a difference in velocityof ~820 km s~(-1).The main structure is dominated by passive galaxies, while these represent -60 of the