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Title: The COS-Halos survey: physical conditions and baryonic mass in the low-redshift circumgalactic medium

We analyze the physical conditions of the cool, photoionized (T ∼10{sup 4} K) circumgalactic medium (CGM) using the COS-Halos suite of gas column density measurements for 44 gaseous halos within 160 kpc of L ∼ L* galaxies at z ∼ 0.2. These data are well described by simple photoionization models, with the gas highly ionized (n {sub H} {sub II}/n {sub H} ≳ 99%) by the extragalactic ultraviolet background. Scaling by estimates for the virial radius, R {sub vir}, we show that the ionization state (tracked by the dimensionless ionization parameter, U) increases with distance from the host galaxy. The ionization parameters imply a decreasing volume density profile n {sub H} = (10{sup –4.2±0.25})(R/R {sub vir}){sup –0.8±0.3}. Our derived gas volume densities are several orders of magnitude lower than predictions from standard two-phase models with a cool medium in pressure equilibrium with a hot, coronal medium expected in virialized halos at this mass scale. Applying the ionization corrections to the H I column densities, we estimate a lower limit to the cool gas mass M{sub CGM}{sup cool}>6.5×10{sup 10} M {sub ☉} for the volume within R < R {sub vir}. Allowing for an additional warm-hot, O VI-traced phase, the CGMmore » accounts for at least half of the baryons purported to be missing from dark matter halos at the 10{sup 12} M {sub ☉} scale.« less
Authors:
; ;  [1] ; ; ; ; ;  [2] ; ;  [3] ;  [4] ;  [5] ;  [6] ;  [7] ;  [8] ;  [9]
  1. UCO/Lick Observatory, University of California, Santa Cruz, CA (United States)
  2. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD (United States)
  3. Department of Astronomy, University of Massachusetts, Amherst, MA (United States)
  4. Department of Physics and Astronomy, University of Notre Dame, South Bend, IN (United States)
  5. Department of Chemistry and Physics, Saint Michael's College, Colchester, VT (United States)
  6. Astronomy Department, University of Arizona, Tucson, AZ 85721 (United States)
  7. Leiden Observatory, Leiden University, NL-2300 RA Leiden (Netherlands)
  8. University of the Western Cape, Bellville, Cape Town 7535 (South Africa)
  9. Department of Astronomy, The Ohio State University, Columbus, OH (United States)
Publication Date:
OSTI Identifier:
22365244
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 792; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; CORRECTIONS; DENSITY; EQUILIBRIUM; FORECASTING; GALAXIES; MASS; NONLUMINOUS MATTER; PHOTOIONIZATION; QUASARS; RED SHIFT; ULTRAVIOLET RADIATION