Halo Masses of MgII absorbers at z ~ 0.5 from SDSS DR7

Creators: Gauthier, Jean-René; Chen, Hsiao-Wen; Cooksey, Kathy L.; Simcoe, Robert A.; Seyffert, Eduardo N.; O'Meara, John M.

Abstract

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 MgII absorber sample and a new LRG sample from SDSS DR7. We present the clustering signal of absorbers on projected scales r_p = 0.3 - 35 h^(-1) Mpc in four W^(λ2796)_r bins spanning W^(λ2796)_r = 0.4 - 5.6Å. We found that on average Mg II absorbers reside in halos (log M_h) ≈ 12.1, similar to the halo mass of an L_* galaxy. We report that the weakest absorbers in our sample with W^(λ2796)_r = 0.4-1.1Å reside in relatively massive halos with (log M_h) ≈ 12.5^(+0.6)_(-1.3), while stronger absorbers reside in halos of similar or lower masses (log M_h) 11.6^(+0.9). We compared our bias data points, b, and the frequency distribution function of absorbers, f_W_r, with a simple model incorporating an isothermal density profile to mimic the distribution of absorbing gas in halos. We also compared the bias data points with Tinker & Chen (2008) who developed halo occupation distribution models of Mg II absorbers that are constrained by b and f_W_r. The simple isothermal model can be ruled at a ≈ 2.8σ level mostly because of its inability to reproduce f_W_r. However, b values are consistent with both models, including TC08. In addition, we show that the mean b of absorbers does not decrease beyond W^(λ2796)_r ≈ 1.6Å. The flat or potential upturn of b for W^(λ2796)-r ≳ 1.6Å absorbers suggests the presence of additional cool gas in massive halos.

Additional Information

It is a pleasure to thank Michael Rauch and Jeremy Tin- ker for helpful comments and discussions. JRG gratefully acknowledges the financial support of a Millikan Fellowship provided by Caltech. The SDSS MgII catalog (Seyffert et al. 2013) was funded largely by the National Science Foundation Astronomy & Astrophysics Postdoctoral Fellowship (AST-1003139) and in part by the MIT Undergraduate Research Opportunity Program (UROP) Direct Funding, from the Office of Undergraduate Advising and Academic Programming and the John Reed UROP Fund. We are grateful to the SDSS collaboration for producing and maintaining the SDSS public data archive. Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. The SDSS Web Site is http://www.sdss.org/. The SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions. The Participating Institutions are the American Museum of Natural History, Astrophysical Institute Potsdam, University of Basel, University of Cambridge, Case Western Reserve University, University of Chicago, Drexel University, Fermilab, the Institute for Advanced Study, the Japan Participation Group, Johns Hopkins University, the Joint Institute for Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences (LAMOST), Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, Ohio State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington.

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