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 0.4 ≤z≤ 0.8 . The Mg ii systems were selected to have λλ 2796 and 2803 rest-frame equivalent widths ≥1.0 Å and identifications confirmed by the Fe iiλ2600 or Mg iλ2852 lines. Over comoving scales 0.05–13 h−1 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 halo masses greater than 3.5 × 1012 M⊙ for MR≲−21 , this relative amplitude implies that the absorber host galaxies have halo masses greater than ∼2–8 × 1011 M⊙ . For 1013-M⊙ LRGs, the absorber host galaxies have halo masses ∼0.5–2.5 × 1012 M⊙ . Our results appear consistent with those of Steidel, Dickinson & Persson (1994) who found that Mg ii absorbers with WMg IIr≥ 0.3 Å are associated with ∼ 0.7L*B galaxies.