Massive Dark Matter Halos around Bright Isolated Galaxies in the 2dFGRS

TL;DR

This study uses the 2dFGRS to analyze the dark matter halos around isolated bright galaxies by examining satellite dynamics, revealing massive halos that vary with galaxy type and luminosity.

Contribution

It introduces a robust method for estimating galaxy halo masses from satellite velocities, validated with simulations, and applies it to derive halo masses for different galaxy types.

Findings

Massive dark matter halos are associated with bright isolated galaxies.

Halo mass estimates depend on galaxy morphology and luminosity.

The method provides unbiased velocity dispersion estimates when isolation criteria are strict.

Abstract

We identify a large sample of isolated bright galaxies and their fainter satellites in the 2dF Galaxy Redshift Survey (2dFGRS). We analyse the dynamics of ensembles of these galaxies selected according to luminosity and morphological type by stacking the positions of their satellites and estimating the velocity dispersion of the combined set. We test our methodology using realistic mock catalogues constructed from cosmological simulations. The method returns an unbiased estimate of the velocity dispersion provided that the isolation criterion is strict enough to avoid contamination and that the scatter in halo mass at fixed primary luminosity is small. Using a maximum likelihood estimator that accounts for interlopers, we determine the satellite velocity dispersion within a projected radius of 175 kpc/h. The dispersion increases with the luminosity of the primary and is larger for elliptical galaxies than for spiral galaxies of similar bJ luminosity. Calibrating the mass-velocity dispersion relation using our mock catalogues, we find a dynamical mass within 175 kpc/h of M_175 ~ 4.0^{+2.3}_{-1.5} 10^12 (L_bJ/L_*) M_sol/h for elliptical galaxies and M_175 ~ 6.3^{+6.3}_{-3.1} 10^11 (L_bJ/L_*)^1.6 Msol/h for spiral galaxies. Finally, we compare our results with recent studies and investigate their limitations using our mock catalogues.