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

We study the cross-correlation between 716 Mg II quasar absorption systems and ∼ 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 Mg II systems were selected to have ΛΛ 2796 & 2803 rest-frame equivalent widths ≥ 1.0 Å and identifications confirmed by the feii Λ 2600 or MgI Λ 2852 lines. Over co-moving scales 0.2-13h^-1{ 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 10¹³ M_⊙, this strong cross-correlation signal implies that the absorber host-galaxies have halo-masses 1-2× 10¹² M_⊙.