The enrichment of the intergalactic medium with adiabatic feedback - I. Metal cooling and metal diffusion

Abstract

A study of metal enrichment of the intergalactic medium (IGM) using a series of smooth particle hydrodynamic (SPH) simulations is presented, employing models for metal cooling and the turbulent diffusion of metals and thermal energy. An adiabatic feedback mechanism was adopted where gas cooling was prevented on the time-scale of supernova bubble expansion to generate galactic winds without explicit wind particles. The simulations produced a cosmic star formation history (SFH) that is broadly consistent with observations until z ∼ 0.5, and a steady evolution of the universal neutral hydrogen fraction ( H I ) that compares reasonably well with observations. The evolution of the mass and metallicities in stars and various gas phases was investigated. At z = 0, about 40 per cent of the baryons are in the warm-hot intergalactic medium (WHIM), but most metals (80-90 per cent) are locked in stars. At higher redshifts the proportion of metals in the IGM is higher due to more efficient loss from galaxies. The results also indicate that IGM metals primarily reside in the WHIM throughout cosmic history, which differs from simulations with hydrodynamically decoupled explicit winds. The metallicity of the WHIM lies between 0.01 and 0.1 solar with a slight decrease at lower redshifts. The metallicity evolution of the gas inside galaxies is broadly consistent with observations, but the diffuse IGM is under enriched at z ∼ 2.5.Galactic winds most efficiently enrich the IGM for haloes in the intermediate mass range 10 10 -10 11 M . At the low-mass end gas is prevented from accreting on to haloes and has very low metallicities. At the high-mass end, the fraction of halo baryons escaped as winds declines along with the decline of stellar mass fraction of the galaxies. This is likely because of the decrease in star formation activity and decrease in wind escape efficiency. Metals enhance cooling which allows WHIM gas to cool on to galaxies and increases star formation. Metal diffusion allows winds to mix prior to escape, decreasing the IGM metal content in favour of gas within galactic haloes and star-forming gas. Diffusion significantly increases the amount of gas with low metallicities and changes the density-metallicity relation.The intergalactic medium (IGM) contains most of the baryons in the Universe, and provides the fuel for galaxies to form stars in which metals are produced. In turn, supernovae (SNe) and galactic winds enrich the IGM with metals, while stars and active galactic nuclei (AGN) emit UV photons. This interplay between the IGM and galaxies, mediated by metal cooling in the presence of UV, regulates the formation of stars in the Universe. The evolution and enrichment history of the IGM provides a record of this interplay.

In-N-Out: The Gas Cycle From Dwarfs to Spiral Galaxies

“…Additional cooling takes place via metal lines (Shen et al 2010). The metal-line cooling rates used in the code are tabulated based on the gas temperature, density, and metallicity and the cosmic UV background.…”

“…They are also injected by stellar winds using a model for mass loss that follows Weidemann (1987) and assumes that the metallicity is that of the stellar particle. Metals are further distributed throughout the gas by diffusion (Shen et al 2010). Star formation proceeds probabilistically, according to the gas density and H 2 fraction.…”

Rhapsody-G simulations I: the cool cores, hot gas and stellar content of massive galaxy clusters

“…We note that standard SPH does not include any mixing of metals (or any tracers, although explicit metal diffusion can be added, see e.g. Shen et al 2010). Planelles et al (2014) included a smoothed metallicity estimate when calculating cooling times and state that their unsmoothed metallicity field is very noisy.…”

NIHAO IX: the role of gas inflows and outflows in driving the contraction and expansion of cold dark matter haloes

“…MUGS and MaGICC use the original version, while NIHAO uses the version of gasoline from Keller et al (2014) that reduces the formation of blobs and improves mixing. Both versions of gasoline use the same treatment for cooling via hydrogen, helium, and various metal-lines in a uniform ultraviolet ionizing background as described in Shen et al (2010).…”