The circumgalactic medium of massive galaxies at z∼ 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 post-processing. The CGM (defined as all gas at R > 0.2 R 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 > 105 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 the galactocentric impact parameter (scaled to the virial radius) that are in broad agreement with those observed at high redshift by Steidel et al. 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 >~ 5 R 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 H I>1017.2 cm-2 material is 27%, in agreement with recent observations by Rudie et al. 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, are the origin of strong (N C II>1013 cm-2) C II absorption with a covering factor of 22% within R vir and 10% within 2 R 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 O VI >~ 1014 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. 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.