Star formation sustained by gas accretion

TL;DR

This paper reviews how cosmic gas accretion influences star formation, summarizing physical properties, observational evidence, and the significance of gas inflow especially at high redshift, to explain galaxy evolution.

Contribution

It compiles and analyzes observational and theoretical evidence for gas accretion's role in sustaining star formation and explains related galaxy properties.

Findings

Gas accretion explains the fundamental metallicity relationship.

Evidence from neutral and ionized hydrogen supports ongoing gas inflow.

High-redshift observations indicate gas accretion's importance in early universe star formation.

Abstract

This paper discusses how cosmic gas accretion controls star formation, and summarizes the physical properties expected for the cosmic gas accreted by galaxies. The paper also collects observational evidence for gas accretion sustaining star formation. It reviews evidence inferred from neutral and ionized hydrogen, as well as from stars. A number of properties characterizing large samples of star-forming galaxies can be explained by metal-poor gas accretion, in particular, the relationship between stellar mass, metallicity, and star formation rate (the so-called fundamental metallicity relationship). They are put forward and analyzed. Theory predicts gas accretion to be particularly important at high redshift, so indications based on distant objects are reviewed, including the global star formation history of the universe, and the gas around galaxies as inferred from absorption features in the spectra of background sources.