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arXiv · 1309.6317

The COS-Halos Survey: Rationale, Design, and A Census of Circumgalactic Neutral Hydrogen

Jason Tumlinson·Christopher Thom·Jessica Werk·J. Xavier Prochaska·Todd Tripp·Neal Katz·Romeel Dave·Benjamin D. Oppenheimer·Joseph Meiring·Amanda Brady Ford·John O'Meara·Molly Peeples·Ken Sembach·David Weinberg
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Abstract

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_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* / Msun= 9.5 - 11.5. We find that the CGM exhibits strong HI, averaging 1 Ang in Lya 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 HI. 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^-1 of the galaxies. This material generally exists well below the halo virial temperatures at T<~ 10^5 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 HI 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.

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Jason Tumlinson, Christopher Thom, Jessica Werk, J. Xavier Prochaska, Todd Tripp, Neal Katz, Romeel Dave, Benjamin D. Oppenheimer, Joseph Meiring, Amanda Brady Ford, John O'Meara, Molly Peeples, Ken Sembach, David Weinberg. 2013-09-24. The COS-Halos Survey: Rationale, Design, and A Census of Circumgalactic Neutral Hydrogen. https://doi.org/10.1088/0004-637x%2F777%2F1%2F59

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