The clustering of Luminous Red Galaxies around Mg II absorbers

We study the cross-correlation between 212 Mg II quasar absorption systems and ∼ 20,000 Luminous Red Galaxies (LRGs) selected from the Sloan Digital Sky Survey Data Release 1 in the redshift range 0.46 z6 0.8. The Mg II systems were selected to have λλ2796 & 2803 rest-frame equivalent widths >1.0 Å and identifications confirmed by the Fe II λ2600 or Mg I λ2852 lines. Over comoving scales 0.05–13h Mpc, the Mg II–LRG cross-correlation has an amplitude 0.67 ± 0.09 times that of the LRG–LRG auto-correlation. Since LRGs have halomasses greater than 3.5 × 10 M⊙ for MR . −21, this relative amplitude implies that the absorber host-galaxies have halo-masses greater than ∼ 2–8× 10 M⊙. For 10 M⊙ LRGs, the absorber host-galaxies have halo-masses 0.5–2.5×10 M⊙. Our results appear consistent with those of Steidel et al. (1994) who found that Mg II absorbers with W r > 0.3 Å are associated with ∼0.7L B galaxies.