Measuring the halo mass of Mg II absorbers from their cross-correlation with Luminous Red Galaxies

We study the cross-correlation between 716 MgII quasar absorption systems and about 100,000 Luminous Red Galaxies (LRGs) selected from the Sloan Digital Sky Survey Data Release 3 in the redshift range 0.4 < z < 0.8. The MgII systems were selected to have 2796 & 2803 rest-frame equivalent widths greater than 1.0 AA and identifications confirmed by the FeII 2600 or MgI 2852 lines. Over co-moving scales 0.2--13/h Mpc, the MgII--LRG cross-correlation has an amplitude 0.69+/-0.09 times that of the LRG--LRG auto-correlation. Since LRGs have halo-masses of 10^{13} msun, this strong cross-correlation implies that the absorber host-galaxies have halo-masses 1--2 times 10^{12} msun.