THE CIRCUMGALACTIC MEDIUM OF MASSIVE GALAXIES ATz∼ 3: A TEST FOR STELLAR FEEDBACK, GALACTIC OUTFLOWS, AND COLD STREAMS

Abstract

We present new results on the kinematics, thermal and ionization state, and spatial distribution of metal-enriched gas in the circumgalactic medium (CGM) of massive galaxies at redshift ∼ 3, using the "Eris" suite of cosmological hydrodynamic "zoom-in" simulations. The reference run adopts a blastwave scheme for supernova feedback that produces large-scale galactic outflows, a star formation recipe based on a high gas density threshold, metal-dependent radiative cooling, and a model for the diffusion of metals and thermal energy. The effect of the local UV radiation field is added in postprocessing. The CGM (defined as all gas at R > 0.2R vir = 10 kpc, where R vir is the virial radius) contains multiple phases having a wide range of physical conditions, with more than half of its heavy elements locked in a warm-hot component at T > 10 5 K. Synthetic spectra, generated by drawing sightlines through the CGM, produce interstellar absorption line strengths of Lyα, C II, C IV, Si II, and Si IV as a function of galactocentric impact parameter (scaled to the virial radius) that are in broad agreement with those observed at high-redshift by Steidel et al. (2010). The covering factor of absorbing material declines less rapidly with impact parameter for Lyα and C IV compared to C II, Si IV, and Si II, with Lyα remaining strong (W Lyα > 300 mÅ) to ∼ > 5R vir = 250 kpc. Only about one third of all the gas within R vir is outflowing. The fraction of sightlines within one virial radius that intercept optically thick, N HI > 10 17.2 cm −2 material is 27%, in agreement with recent observations by Rudie et al. (2012). Such optically thick absorption is shown to trace inflowing "cold" streams that penetrate deep inside the virial radius. The streams, enriched to metallicities above 0.01 solar by previous episodes of star formation in the main host and in nearby dwarfs, give origin to strong (N CII > 10 13 cm −2 ) C II absorption with a covering factor of 22% within R vir and 10% within 2R vir . Galactic outflows do not cause any substantial suppression of the cold accretion mode. The central galaxy is surrounded by a large O VI halo, with a typical column density N OVI ∼ > 10 14 cm −2 and a near unity covering factor maintained all the way out to 150 kpc. This matches the trends recently observed in star-forming galaxies at low redshift by Tumlinson et al. (2011). Our zoom-in simulations of this single system appear then to reproduce quantitatively the complex baryonic processes that determine the exchange of matter, energy, and metals between galaxies and their surroundings.

EVIDENCE FOR UBIQUITOUS COLLIMATED GALACTIC-SCALE OUTFLOWS ALONG THE STAR-FORMING SEQUENCE ATz∼ 0.5

“…We speculate that this trend is driven in part by absorption from virialized CGM gas along the line of sight, the kinematics of which may be closely tied to the halo mass of the host galaxy. We emphasize that this hypothesis is not substantiated by the analysis presented here, and must be tested via empirical constraints on the spatial extent of outflows and in cosmological "zoom-in" simulations of galaxy formation in individual halos (e.g., Shen et al 2013;Stinson et al 2012). Martin et al (2012) also found a positive correlation between M * and the maximum negative velocity at which the Mg ii absorption profile meets the continuum, though the trend was only marginally significant (1.8σ ).…”

“…Comparison of observed cool gas kinematics with results from hydrodynamic simulations of individual galaxy halos which implement a wide range of wind prescriptions is a promising avenue for constraining the physics relevant to cool outflows, or alternatively for understanding the limitations of these data in establishing such constraints. Simulations tracking the enrichment of gaseous halos with hydrogen and metals have already been used to better understand feedback models via comparison of "observations" of the gas distribution along sightlines through the simulated halos with QSO absorption line studies (Fumagalli et al 2011;Shen et al 2013;Stinson et al 2012). Similar analysis of gas dynamics "down-the-barrel" toward simulated galaxies may be directly compared to the measurements described here, providing new insight into the origins, energetics, and fate of galactic outflows.…”

The Properties of the Circumgalactic Medium in Red and Blue Galaxies: Results From the Cos-Gass+cos-Halos Surveys

“…In any event, we believe the data we have presented here provide a valuable observational resource for ongoing and future numerical simulations that try to reproduce CGM properties such as Lyαand metal-line column density profiles, covering fraction, and dynamics, such as line-widths and velocity spreads (for example Hummels et al 2012;Stinson et al 2012;Ford et al 2013Ford et al , 2014Ford et al , 2016Shen et al 2013;Fielding et al 2016;Kauffmann et al 2016;Liang et al 2016, and references therein). The ultimate goal is understanding the role of the CGM in the evolution of galaxies.…”

Gas around galaxy haloes - III: hydrogen absorption signatures around galaxies and QSOs in the Sherwood simulation suite

“…This is consistent with the values found for the FIRE simulations . By contrast, the mass loading factor was less than unity for the galaxy in Shen et al (2013). Mass loading factors have not been published for the EAGLE simulations.…”