Halo Occupation of MgII Absorbers Jeremy Tinker Hsiao-Wen Chen University of Chicago Binney & Tremaine

What are MgII Absorbers? Dark matter halo, galaxy at center, cold gas probed by MgII in halo. Chuck Steidel 2796, 2803

Visualizations of Sloan Data courtesy of Mark Subbarao

Visualizations of Sloan Data courtesy of Mark Subbarao

What do (we think) they mean? Small halo = lower column density, lower dispersion, weaker absorber (equivalent width W [A]) Big halo = lots of gas, large dispersion, stronger absorber.

Clustering Bias of MgII Systems Bouche et al (2006): bias relative to LRGs as a function of W: anti-correlation!Bouche et al (2006): bias relative to LRGs as a function of W: anti-correlation! Distribution of impact parameters: “strong absorbers preferentially at low impact parameters.”Distribution of impact parameters: “strong absorbers preferentially at low impact parameters.”

Halo-Based Model C g - covering fraction x incidence. A W -encompass MgII gas fraction and density-EW relation. core-isothermal density profile of MgII gas. Low-mass halo High-mass halo P(  b ) - PDF of impact parameters

Results Mass points are estimated by Bouche et al from b(w). Not used in model fitting. Data Used: -Frequency (number per unit distance) -Bias relative to LRGs. -Model: 6 free parameters. (47 data points) -  A =-0.13

Dekel & Birnboim 2006 Keres et al Low Mass = Cold Gas (T~10 4 K) High Mass = Hot Gas (T>10 6 K) no MgII Transition mass scale: shock heating occurs as an inside-out process. Simulations predict that this process occurs over 1-2 dex in halo mass. In the hot mode, some cold gas still exists. Cold vs. Hot Halo Gas

Results Mass points are estimated by Bouche et al from b(w). Not used in model fitting. -”Shock” Model: 8 free parameters. -f cold = 6% transition mass  shock =0.8 (transition width of 1.25 dex in mass)

Impact Parameters Points+bars are mean and dispersion for every ten data points.Points+bars are mean and dispersion for every ten data points. Line+shade are mean and dispersion of model (note: these are model predictions).Line+shade are mean and dispersion of model (note: these are model predictions). Dotted line = 99% upper bound on P(W|  b ).Dotted line = 99% upper bound on P(W|  b ). NB! - take these data with grain of salt: incomplete at low  b and possibly biased. Use for sanity check only.NB! - take these data with grain of salt: incomplete at low  b and possibly biased. Use for sanity check only.

Conclusions Proof of concept: Toward constraining the distribution of cold gas across the halo mass spectrum.Proof of concept: Toward constraining the distribution of cold gas across the halo mass spectrum. Models without a hot-cold transition cannot fit the data.Models without a hot-cold transition cannot fit the data.