Two fossil groups of galaxies at zp 0.4 in the Cosmic Evolution Survey: accelerated stellar-mass build-up, different progenitors
Keywords
galaxies: evolution, galaxies: groups: general, galaxies: luminosity function, mass function, X-rays: galaxies: clusters
Abstract
We report on 2 fossil groups of galaxies at z=0.425 and 0.372 discovered in the Cosmic Evolution Survey (COSMOS) area. Selected as X-ray extended sources, they have total masses (M_200) of 1.9(_s16/-0.41)E13 and 9.5(_s16/-0.42)E13 M_sun, respectively, as obtained from a recent X-ray luminosity-mass scaling relation. The lower mass system appears isolated, whereas the other sits in a well-known large-scale structure (LSS) populated by 27 other X-ray emitting groups. The identification as fossil is based on the i-band photometry of all the galaxies with a photo-z consistent with that of the group at the 2-sigma confidence level and within a projected group-centric distance equal to 0.5R_200, and i_AB
