The COS-Halos Survey: Metallicities in the Low-redshift Circumgalactic Medium
- University of California, Santa Cruz, CA (United States)
- Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany)
- Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003-9305 (United States)
- Space Telescope Science Institute, Baltimore, MD 21218 (United States)
- Institute for Computational Cosmology and Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham, DH1 3LE (United Kingdom)
- Center of Astrophysics, Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States)
- Millennium Institute of Astrophysics, Santiago (Chile)
We analyze new far-ultraviolet spectra of 13 quasars from the z∼0.2 COS-Halos survey that cover the H i Lyman limit of 14 circumgalactic medium (CGM) systems. These data yield precise estimates or more constraining limits than previous COS-Halos measurements on the H i column densities N{sub HI}. We then apply a Monte-Carlo Markov chain approach on 32 systems from COS-Halos to estimate the metallicity of the cool (T∼10{sup 4} K) CGM gas that gives rise to low-ionization state metal lines, under the assumption of photoionization equilibrium with the extragalactic UV background. The principle results are: (1) the CGM of field L* galaxies exhibits a declining H i surface density with impact parameter R{sub ⊥} (at >99.5% confidence), (2) the transmission of ionizing radiation through CGM gas alone is 70 ± 7%; (3) the metallicity distribution function of the cool CGM is unimodal with a median of 10{sup −0.51} Z{sub ⊙} and a 95% interval ≈1/50 Z{sub ⊙} to >3 Z{sub ⊙}; the incidence of metal-poor (<1/100 Z{sub ⊙}) gas is low, implying any such gas discovered along quasar sightlines is typically unrelated to L* galaxies; (4) we find an unexpected increase in gas metallicity with declining N{sub HI} (at >99.9% confidence) and, therefore, also with increasing R{sub ⊥}; the high metallicity at large radii implies early enrichment; and (5) a non-parametric estimate of the cool CGM gas mass is M{sub CGM}{sup cool}=(9.2±4.3)×10{sup 10} M{sub ⊙}, which together with new mass estimates for the hot CGM may resolve the galactic missing baryons problem. Future analyses of halo gas should focus on the underlying astrophysics governing the CGM, rather than processes that simply expel the medium from the halo.
- OSTI ID:
- 22869217
- Journal Information:
- Astrophysical Journal, Vol. 837, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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