Browsing by Author "Tripp, Todd M."
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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 A deep search for faint galaxies associated with very low-redshift C iv absorbers: A case with cold-accretion characteristics(The American Astronomical Society, 2013) Burchett, Joseph N.; Tripp, Todd M.; Werk, Jessica K.; Howk, J. Christopher; Dave, Romeel; Prochaska, J. Xavier; Ford, Amanda BradyStudies of QSO absorber–galaxy connections are often hindered by inadequate information on whether faint/dwarf galaxies are located near the QSO sight lines. To investigate the contribution of faint galaxies to QSO absorber populations, we are conducting a deep galaxy redshift survey near low-z Civ absorbers. Here we report a blindly detected C iv absorption system (zabs = 0.00348) in the spectrum of PG1148+549 that appears to be associated either with an edge-on dwarf galaxy with an obvious disk (UGC 6894, zgal = 0.00283) at an impact parameter of ρ = 190 kpc or with a very faint dwarf irregular galaxy at ρ = 23 kpc, which is closer to the sightline but has a larger redshift difference (zgal = 0.00107, i.e., δv = 724 km s−1). We consider various gas/galaxy associations, including infall and outflows. Based on current theoretical models, we conclude that the absorber is most likely tracing (1) the remnants of an outflow from a previous epoch, a so-called “ancient outflow”, or (2) intergalactic gas accreting onto UGC 6894, “cold mode” accretion. The latter scenario is supported by Hi synthesis imaging data that shows the rotation curve of the disk being codirectional with the velocity offset between UGC 6894 and the absorber, which is located almost directly along the major axis of the edge-on disk.Item The high-ion content and kinematics of low-redshift lyman limit systems(The American Astronomical Society, 2013) Fox, Andrew J.; Lehner, Nicholas; Dave, Romeel; Tumlinson, Jason; Howk, J. Christopher; Tripp, Todd M.; Prochaska, J. Xavier; O'Meara, John M.; Werk, Jessica K.; Bordoloi, Rongmon; Katz, Neal; Oppenheimer, Benjamin D.We study the high-ion content and kinematics of the circumgalactic medium around low-redshift galaxies using a sample of 23 Lyman limit systems (LLSs) at 0.08 < z < 0.93 observed with the Cosmic Origins Spectrograph on board the Hubble Space Telescope. In Lehner et al., we recently showed that low-z LLSs have a bimodal metallicity distribution. Here we extend that analysis to search for differences between the high-ion and kinematic properties of the metal-poor and metal-rich branches. We find that metal-rich LLSs tend to show higher O VI columns and broader O VI profiles than metal-poor LLSs. The total H I line width (Δv 90 statistic) in LLSs is not correlated with metallicity, indicating that the H I kinematics alone cannot be used to distinguish inflow from outflow and gas recycling. Among the 17 LLSs with O VI detections, all but two show evidence of kinematic sub-structure, in the form of O VI-H I centroid offsets, multiple components, or both. Using various scenarios for how the metallicities in the high-ion and low-ion phases of each LLS compare, we constrain the ionized hydrogen column in the O VI phase to lie in the range log N(H II) ~ 17.6-20. The O VI phase of LLSs is a substantial baryon reservoir, with M(high-ion) ~ 108.5-10.9 (r/150 kpc)2 M ☉, similar to the mass in the low-ion phase. Accounting for the O VI phase approximately doubles the contribution of low-z LLSs to the cosmic baryon budget.