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Halo Occupation of MgII Absorbers

Halo Occupation of MgII Absorbers. Jeremy Tinker Hsiao-Wen Chen University of Chicago. Binney & Tremaine. QSO. What are MgII Absorbers?. 2796, 2803. Dark matter halo, galaxy at center, cold gas probed by MgII in halo. Chuck Steidel. Visualizations of Sloan Data.

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Halo Occupation of MgII Absorbers

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

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

  3. Visualizations of Sloan Data courtesy of Mark Subbarao

  4. Visualizations of Sloan Data courtesy of Mark Subbarao

  5. 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.

  6. Clustering Bias of MgII Systems • 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.”

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

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

  9. Dekel & Birnboim 2006 Cold vs. Hot Halo Gas Dekel & Birnboim 2006 Low Mass = Cold Gas (T~104 K) High Mass = Hot Gas (T>106 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. Keres et al. 2005

  10. Results • -”Shock” Model: 8 free parameters. • fcold = 6% • 1011.0 transition mass • shock=0.8 (transition width of 1.25 dex in mass) Mass points are estimated by Bouche et al from b(w). Not used in model fitting.

  11. Impact Parameters • Points+bars are mean and dispersion for every ten data points. • Line+shade are mean and dispersion of model (note: these are model predictions). • 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.

  12. Conclusions • 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.

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