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Title: THE COS-HALOS SURVEY: RATIONALE, DESIGN, AND A CENSUS OF CIRCUMGALACTIC NEUTRAL HYDROGEN

We present the design and methods of the COS-Halos survey, a systematic investigation of the gaseous halos of 44 z = 0.15-0.35 galaxies using background QSOs observed with the Cosmic Origins Spectrograph aboard the Hubble Space Telescope. This survey has yielded 39 spectra of z{sub em} ≅ 0.5 QSOs with S/N ∼10-15 per resolution element. The QSO sightlines pass within 150 physical kpc of the galaxies, which span early and late types over stellar mass log M{sub *}/M{sub ☉} = 9.5-11.5. We find that the circumgalactic medium exhibits strong H I, averaging ≅ 1 Å in Lyα equivalent width out to 150 kpc, with 100% covering fraction for star-forming galaxies and 75% covering for passive galaxies. We find good agreement in column densities between this survey and previous studies over similar range of impact parameter. There is weak evidence for a difference between early- and late-type galaxies in the strength and distribution of H I. Kinematics indicate that the detected material is bound to the host galaxy, such that ∼> 90% of the detected column density is confined within ±200 km s{sup –1} of the galaxies. This material generally exists well below the halo virial temperatures at T ∼< 10{supmore » 5} K. We evaluate a number of possible origin scenarios for the detected material, and in the end favor a simple model in which the bulk of the detected H I arises in a bound, cool, low-density photoionized diffuse medium that is generic to all L* galaxies and may harbor a total gaseous mass comparable to galactic stellar masses.« less
Authors:
; ;  [1] ; ;  [2] ; ; ;  [3] ;  [4] ;  [5] ;  [6] ;  [7] ;  [8] ;  [9]
  1. Space Telescope Science Institute, Baltimore, MD (United States)
  2. UCO/Lick Observatory, University of California, Santa Cruz, CA (United States)
  3. Department of Astronomy, University of Massachusetts, Amherst, MA (United States)
  4. University of the Western Cape, South African Astronomical Observatories, and African Institute for Mathematical Sciences, Cape Town (South Africa)
  5. Leiden Observatory, Leiden University, 2300 RA Leiden (Netherlands)
  6. Steward Observatory, University of Arizona, Tucson, AZ (United States)
  7. Department of Chemistry and Physics, Saint Michael's College, Colchester, VT (United States)
  8. Center for Galaxy Evolution, University of California Los Angeles, Los Angeles, CA (United States)
  9. Department of Astronomy, The Ohio State University, Columbus, OH (United States)
Publication Date:
OSTI Identifier:
22270628
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 777; 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; AMINO ACIDS; ASTRONOMY; ASTROPHYSICS; COMPARATIVE EVALUATIONS; DENSITY; GALAXIES; HYDROGEN; IMPACT PARAMETER; LYMAN LINES; MASS; PHOTOIONIZATION; QUASARS; RESOLUTION; STARS; TELESCOPES