The COS-Halos survey: Rationale, design and a census of circumgalactic neutral hydrogen
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Date
2013
Journal Title
Journal ISSN
Volume Title
Publisher
IOP Publishing
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 zem 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 logM∗/M = 9.5–11.5. We find that the circumgalactic medium exhibits strong Hi, averaging 1Å
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 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 105 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.
Description
Keywords
Galaxies, Formation – galaxies, Halos – intergalactic medium – quasars, Absorption lines
Citation
Tumlinson, J. et al. (2013). The COS-Halos survey: Rationale, design and a census of circumgalactic neutral hydrogen. The Astrophysical Journal , 777 (59): 1-33