Browsing by Author "Katz, Neal"
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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 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.Item The impact of wind scalings on stellar growth and the baryon cycle in cosmological simulations(Oxford University Press, 2020) Dave´, Romeel; Huang, Shuiyao; Katz, NealMany phenomenologically successful cosmological simulations employ kinetic winds to model galactic outflows. Yet systematic studies of how variations in kinetic wind scalings might alter observable galaxy properties are rare. Here we employ GADGET-3 simulations to study how the baryon cycle, stellar mass function, and other galaxy and CGM predictions vary as a function of the assumed outflow speed and the scaling of the mass-loading factor with velocity dispersion. We design our fiducial model to reproduce the measured wind properties at 25 per cent of the virial radius from the Feedback In Realistic Environments simulations.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.Item A New Model For Including Galactic Winds in Simulations of Galaxy Formation II: Implementation of PhEW in Cosmological Simulations(Monthly Notices of the Royal Astronomical Society, 2021) Huang, Shuiyao; Katz, Neal; Dave, RomeelAlthough galactic winds play a critical role in regulating galaxy formation, hydrodynamic cosmological simulations do not resolve the scales that govern the interaction between winds and the ambient circumgalactic medium (CGM). We implement the Physically Evolved Wind (PhEW) model of Huang et al. (2020) in the GIZMO hydrodynamics code and perform test cosmological simulations with different choices of model parameters and numerical resolution. PhEW adopts an explicit subgrid model that treats each wind particle as a collection of clouds that exchange mass, metals, and momentum with their surroundings and evaporate by conduction and hydrodynamic instabilities as calibrated on much higher resolution cloud scale simulations. In contrast to a conventional wind algorithm, we find that PhEW results are robust to numerical resolution and implementation details because the small scale interactions are defined by the model itself. Compared to conventional wind simulations with the same resolution, our PhEW simulations produce similar galaxy stellar mass functions at z ≥ 1 but are in better agreement with low-redshift observations at M∗ < 1011M⊙ because PhEW particles shed mass to the CGM before escaping low mass halos. PhEW radically alters the CGM metal distribution because PhEW particles disperse metals to the ambient medium as their clouds dissipate, producing a CGM metallicity distribution that is skewed but unimodal and is similar between cold and hot gas. While the temperature distributions and radial profiles of gaseous halos are similar in simulations with PhEW and conventional winds, these changes in metal distribution will affect their predicted UV/X-ray properties in absorption and emission.Item A new model for including galactic winds in simulations of galaxy formation – I. Introducing the Physically Evolved Winds (PhEW) model(Oxford University Press, 2020-07-08) Dave, Romeel; Huang, Shuiyao; Katz, NealThe propagation and evolution of cold galactic winds in galactic haloes is crucial to galaxy formation models. However, modelling of this process in hydrodynamic simulations of galaxy formation is oversimplified owing to a lack of numerical resolution and often neglects critical physical processes such as hydrodynamic instabilities and thermal conduction. We propose an analytic model, Physically Evolved Winds, that calculates the evolution of individual clouds moving supersonically through a uniform ambient medium. Our model reproduces predictions from very high resolution cloud-crushing simulations that include isotropic thermal conduction over a wide range of physical conditions. We discuss the implementation of this model into cosmological hydrodynamic simulations of galaxy formation as a subgrid prescription to model galactic winds more robustly both physically and numerically.