Browsing by Author "Weinberg, David H."
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Item The COS-Halos survey: Rationale, design and a census of circumgalactic neutral hydrogen(IOP Publishing, 2013) 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.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.Item The neutral hydrogen content of galaxies in cosmological hydrodynamic simulations(Oxford University Press, 2013) Dave, Romeel; Katz, Neal; Oppenheimer, Benjamin D.; Kollmeier, Juna A.; Weinberg, David H.We examine the global HI properties of galaxies in quarter billion particle cosmological simulations using GADGET-2, focusing on howgalactic outflows impactHI content.We consider four outflow models, including a new one (ezw) motivated by recent interstellar medium simulations in which the wind speed and mass loading factor scale as expected for momentumdriven outflows for larger galaxies and energy-driven outflows for dwarfs (σ <75 km s−1). To obtain predicted HI masses, we employ a simple but effective local correction for particle selfshielding and an observationally constrained transition from neutral to molecular hydrogen. Our ezw simulation produces an HI mass function whose faint-end slope of −1.3 agrees well with observations from the Arecibo Fast Legacy ALFA survey; other models agree less well. Satellite galaxies have a bimodal distribution in HI fraction versus halo mass, with smaller satellites and/or those in larger haloes more often being HI deficient. At a given stellar mass, HI content correlates with the star formation rate and inversely correlates with metallicity, as expected if driven by stochasticity in the accretion rate. To higher redshifts, massive HI galaxies disappear and the mass function steepens. The global cosmic HI density conspires to remain fairly constant from z ∼ 5→0, but the relative contribution from smaller galaxies increases with redshift.