The COS-Halos survey: Rationale, design and a census of circumgalactic neutral hydrogen
Date
2013Author
Tumlinson, Jason
Thom, Christopher
Dave, Romeel
Werk, Jessica K.
Prochaska, J. Xavier
Tripp, Todd M.
Katz, Neal
Oppenheimer, Benjamin D.
Meiring, Joseph D.
Ford, Amanda Brady
O'Meara, John M.
Peeples, Molly S.
Sembach, Kenneth R.
Weinberg, David H.
Metadata
Show full item recordAbstract
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.