Halo masses of Mg II absorbers at z ∼ 0.5 from Sloan Digital Sky Survey Data Release 7

We present the cross-correlation function of MgII absorbers with respect to a volume-limited sample of luminous red galaxies (LRGs) at z = 0.45-0.60 using the largest Mg II absorber sample and a new LRG sample from Sloan Digital Sky Survey Data Release 7. We present the clustering signal of absorbers on projected scales r(p) = 0.3-35 h(-1)Mpc in four W-r(lambda 2796) bins spanning W-r(lambda 2796) = 0.4-5.6 angstrom. We found that on average MgII absorbers reside in haloes < log M-h > approximate to 12.1, similar to the halomass of an L-* galaxy. We report that the weakest absorbers in our sample with W-r(lambda 2796) = 0.4-1.1 angstrom reside in relatively massive haloes with < log M-h > approximate to 12.5(-1.3)(+0.6), while stronger absorbers reside in haloes of similar or lower masses < log M-h > approximate to 11.6(+0.9). We compared our bias data points, b, and the frequency distribution function of absorbers, f(Wr), with a simple model incorporating an isothermal density profile to mimic the distribution of absorbing gas in haloes. We also compared the bias data points with Tinker & Chen who developed halo occupation distribution models of Mg II absorbers that are constrained by b and f(Wr). The simple isothermal model can be ruled at a approximate to 2.8 sigma level mostly because of its inability to reproduce f(Wr). However, b values are consistent with both models, including Tinker & Chen. In addition, we show that the mean b of absorbers does not decrease beyond W-r(lambda 2796) approximate to 1.6 angstrom. The flat or potential upturn of b for W-r(lambda 2796) greater than or similar to 1.6 angstrom absorbers suggests the presence of additional cool gas in massive haloes.