The Enrichment of the Intergalactic Medium with Adiabatic Feedback I: Metal Cooling and Metal Diffusion

TL;DR

This paper uses SPH simulations with metal cooling and diffusion to study how the intergalactic medium (IGM) gets enriched with metals, revealing the roles of galactic winds, halo mass, and metal diffusion in cosmic metal distribution.

Contribution

It introduces a novel simulation approach incorporating metal cooling and turbulent diffusion, providing new insights into IGM enrichment and galaxy feedback mechanisms.

Findings

IGM metals mainly reside in the WHIM across cosmic time.

Galactic winds enrich the IGM most effectively in halos of 10^{10}-10^{11} M_sun.

Metal diffusion increases low-metallicity gas and alters the density-metallicity relation.

Abstract

A study of the IGM metal enrichment using a series of SPH simulations is presented, employing metal cooling and turbulent diffusion of metals and thermal energy. An adiabatic feedback mechanism was adopted where gas cooling was prevented 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 $\sim$ 0.5, and a steady evolution of the universal neutral hydrogen fraction ($\Omega_{\rm H I}$). At z=0, about 40% of the baryons are in the warm-hot intergalactic medium (WHIM), but most metals (80%-90%) are locked in stars. At higher z the proportion of metals in the IGM is higher due to more efficient loss from galaxies. The IGM metals primarily reside in the WHIM throughout cosmic history. The metallicity evolution of the gas inside galaxies is broadly consistent with observations, but the diffuse IGM is under enriched at z $\sim$ 2.5. Galactic winds most efficiently enrich the IGM for halos in the intermediate mass range $10^{10}$M$_{\sun}$ - $10^{11}$ M$_{\sun}$. At the low mass end gas is prevented from accreting onto halos 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 in wind escape efficiency. Metals enhance cooling which allows WHIM gas to cool onto 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 halos and star forming gas. Diffusion significantly increases the amount of gas with low metallicities and changes the density-metallicity relation.