Galaxy Groups at Intermediate Redshift

Galaxy groups likely to be virialized are identified within the CNOC2intermediate redshift galaxy survey using an iterative method. Thenumber-velocity dispersion relation is in agreement with the low-massextrapolation of the cluster normalized Press-Schechter function. The two-pointgroup-group correlation function has r_0=6.8+/- 0.3 Mpc, which is larger thanthe correlations of individual galaxies at the level predicted from n-bodycalibrated halo clustering. The groups are stacked in velocity and position to create a sample largeenough for measurement of a density and velocity dispersion profile. Thestacked mean galaxy density profile falls nearly as a power law with r^{-2.5}and has no well-defined core. The projected velocity dispersion is examined fora variety of samples with different methods and found to be either flat orslowly rising outwards. The combination of a steeper-than-isothermal densityprofile and the outward rising velocity dispersion implies that themass-to-light ratio of groups rises with radius. The M/L can be kept nearlyconstant if the galaxy orbits are nearly circular, although such strongtangential anisotropy is not supported by other evidence. The segregation ofmass and light is not dependent on galaxy luminosity but is far more prominentin the red galaxies than the blue. The M/L gradient could arise from orbital``sloshing'' of the galaxies in the group halos, dynamical friction acting onthe galaxies in a background of ``classical'' collisionless dark matter, or,more speculatively, the dark matter may have a true core.Comment: 50 pages, 24 figures, submitted to Ap