1206.3566 (Cheng Li et al.)

Kinematics of groups of galaxies in the Sloan Digital Sky Survey data release 7    [PDF]

Cheng Li, Y. P. Jing, Shude Mao, Jiaxin Han, Qiuying Peng, Xiaohu Yang, H. J. Mo, Frank van den Bosch

(Abridged) We present measurements of the velocity dispersion profile (VDP) for different masses of galaxy groups, using ~16,000 groups selected from the final data release of the SDSS by Yang et al (2007). We divide the groups into subsamples according to the stellar mass of their central galaxy, and for each subsample we estimate the redshift-space cross-correlation function (CCF) with respect to a reference sample, xi(r_p,pi), as well as the projected CCF, w_p(r_p). An NFW profile plus a biased version of the linear mass autocorrelation function can well describe the observed w_p(r_p), providing an accurate determination of the real-space CCF xi(r). The one-dimensional VDP is extracted from the redshift distortion in xi(r_p,pi), by comparing xi(r_p,pi) with xi(r). We find that the velocity dispersion (VD) within the virial radius (R_200) shows a roughly flat profile, with a slight increase at <~ 0.3 R_200. The average VD within R_200, sigma_v, is a strongly increasing function of central galaxy mass, ranging from ~130km/s at M*~3x10^10 M_sun, up to ~650km/s at M*~5x10^11 M_sun. We extend our analysis to N-body simulations with the LCDM cosmology but different density fluctuation amplitudes, sigma_8. We apply the abundance matching model to assign a stellar mass to the central subhalos. We measure the VDP for the halos and compare the results to the data. We show that the sigma_v-M* relation provides stringent constraints on both sigma_8 and sigma_ms, the dispersion in log(M*) of central galaxies at fixed halo mass. Our data suggests sigma_8=0.86+/-0.03 and sigma_ms=0.16+/-0.03. The slightly higher sigma_8 compared to the WMAP7 result might be due to a smaller matter density parameter assumed in our simulations. Our sigma_v measurements also provide a direct measure of the halo masses, agreeing well with the results from the galaxy-galaxy lensing analysis by Mandelbaum et al. (2006).

View original: http://arxiv.org/abs/1206.3566