THE COS-HALOS SURVEY: RATIONALE, DESIGN, AND A CENSUS OF CIRCUMGALACTIC NEUTRAL HYDROGEN
- Space Telescope Science Institute, Baltimore, MD (United States)
- UCO/Lick Observatory, University of California, Santa Cruz, CA (United States)
- Department of Astronomy, University of Massachusetts, Amherst, MA (United States)
- University of the Western Cape, South African Astronomical Observatories, and African Institute for Mathematical Sciences, Cape Town (South Africa)
- Leiden Observatory, Leiden University, 2300 RA Leiden (Netherlands)
- Steward Observatory, University of Arizona, Tucson, AZ (United States)
- Department of Chemistry and Physics, Saint Michael's College, Colchester, VT (United States)
- Center for Galaxy Evolution, University of California Los Angeles, Los Angeles, CA (United States)
- Department of Astronomy, The Ohio State University, Columbus, OH (United States)
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{sup 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.
- OSTI ID:
- 22270628
- Journal Information:
- Astrophysical Journal, Vol. 777, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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