THE GASEOUS ENVIRONMENT OF HIGH-z GALAXIES: PRECISION MEASUREMENTS OF NEUTRAL HYDROGEN IN THE CIRCUMGALACTIC MEDIUM OF z {approx} 2-3 GALAXIES IN THE KECK BARYONIC STRUCTURE SURVEY
- Cahill Center for Astronomy and Astrophysics, California Institute of Technology, MS 249-17, Pasadena, CA 91125 (United States)
- Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands)
- Astronomical Observatory, Volgina 7, 11060 Belgrade (Serbia)
- Institute of Astronomy, Madingley Road, Cambridge CB3 0HA (United Kingdom)
- National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States)
- Department of Astronomy, University of California, Los Angeles, 430 Portola Plaza, Los Angeles, CA 90024 (United States)
- Department of Physics, University of Wisconsin Milwaukee, Milwaukee, WI 53211 (United States)
We present results from the Keck Baryonic Structure Survey (KBSS), a unique spectroscopic survey of the distant universe designed to explore the details of the connection between galaxies and intergalactic baryons within the same survey volumes, focusing particularly on scales from {approx}50 kpc to a few Mpc. The KBSS is optimized for the redshift range z {approx} 2-3, combining S/N {approx}100 Keck/HIRES spectra of 15 of the brightest QSOs in the sky at z {approx_equal} 2.5-2.9 with very densely sampled galaxy redshift surveys within a few arcmin of each QSO sightline. In this paper, we present quantitative results on the distribution, column density, kinematics, and absorber line widths of neutral hydrogen (H I) surrounding a subset of 886 KBSS star-forming galaxies with 2.0 {approx}< z {approx}< 2.8 and with projected distances {<=}3 physical Mpc from a QSO sightline. Using Voigt profile decompositions of the full Ly{alpha} forest region of all 15 QSO spectra, we compiled a catalog of {approx}6000 individual absorbers in the redshift range of interest, with 12 {<=} log (N{sub HI}) {<=}21. These are used to measure H I absorption statistics near the redshifts of foreground galaxies as a function of projected galactocentric distance from the QSO sightline and for randomly chosen locations in the intergalactic medium (IGM) within the survey volume. We find that N{sub HI} and the multiplicity of velocity-associated H I components increase rapidly with decreasing galactocentric impact parameter and as the systemic redshift of the galaxy is approached. The strongest H I absorbers within {approx_equal} 100 physical kpc of galaxies have N{sub HI} {approx}3 orders of magnitude higher than those near random locations in the IGM. The circumgalactic zone of most significantly enhanced H I absorption is found within transverse distances of {approx}< 300 kpc and within {+-}300 km s{sup -1} of galaxy systemic redshifts. Taking this region as the defining bounds of the circumgalactic medium (CGM), nearly half of absorbers with log(N{sub HI}) > 15.5 are found within the CGM of galaxies meeting our photometric selection criteria, while their CGM occupy only 1.5% of the cosmic volume. The spatial covering fraction, multiplicity of absorption components, and characteristic N{sub HI} remain significantly elevated to transverse distances of {approx}2 physical Mpc from galaxies in our sample. Absorbers with N{sub HI} >10{sup 14.5} cm{sup -2} are tightly correlated with the positions of galaxies, while absorbers with lower N{sub HI} are correlated with galaxy positions only on {approx}>Mpc scales. Redshift anisotropies on these larger scales indicate coherent infall toward galaxy locations, while on scales of {approx}100 physical kpc peculiar velocities of {Delta}v {approx_equal} {+-}260 km s{sup -1} with respect to the galaxies are indicated. The median Doppler widths of individual absorbers within 1-3 r{sub vir} of galaxies are larger by {approx_equal} 50% than randomly chosen absorbers of the same N{sub HI}, suggesting higher gas temperatures and/or increased turbulence likely caused by some combination of accretion shocks and galactic winds around galaxies with M{sub halo} {approx_equal} 10{sup 12} M{sub Sun} at z {approx} 2-3.
- OSTI ID:
- 22034550
- Journal Information:
- Astrophysical Journal, Vol. 750, 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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