Concordance between the Dynamics of Satellite Galaxies in the 2dFGRS and Lambda-CDM

Abstract

We compute the velocity dispersion profile, \sigmav(r_p), for satellites of host galaxies in the Two Degree Field Galaxy Redshift Survey (2dFGRS) and in the Lambda-CDM GIF simulation. We find 1345 hosts in the 2dFGRS with luminosities in the range 0.5 L* < L < 5.5 L*, for which a total of 2475 satellite galaxies is obtained. The magnitudes of the galaxies in the GIF simulation are converted to the b_J band pass, and hosts and satellites are selected in the same manner as in the 2dFGRS. Of order 1200 hosts and 4100 satellites are found in the simulation. Overall, there is excellent agreement between \sigmav(r_p) for the satellites in the 2dFGRS and the GIF simulation. On large scales, \sigmav(r_p) decreases with projected radius, in good agreement with the expectations of a CDM universe. Further, there is a marked dependence of \sigmav(r_p) on both the host spectral type and the host luminosity. In particular, \sigmav(r_p) has a substantially higher amplitude and steeper slope for satellites of early-type hosts than it does for satellites of late-type hosts. In addition, both the amplitude and slope of \sigmav(r_p) increase with host luminosity. The velocity dispersion of satellites located within small projected radii (r_p < 120 kpc) is only marginally consistent with the local B-band Tully-Fisher relation, and is fitted best by a relationship of the form σ_v \propto L^{0.45 \pm 0.10}.