Evolution of Gas, and Star Formation from z = 0 to 5

TL;DR

This study uses ALMA data to analyze how gas content and star formation efficiencies have evolved from redshift 0 to 5, revealing that gas mass primarily drives early star formation, while efficiency influences starbursts.

Contribution

It provides new insights into the relative roles of gas mass and star formation efficiency in galaxy evolution from z=0 to 5, based on a large ALMA galaxy sample.

Findings

Gas mass increase accounts for 70% of SFR rise on the main sequence.

Starburst activity is mainly driven by enhanced star formation efficiency.

Interstellar gas peaks at z=2 and influences galaxy evolution down to z=1.2.

Abstract

ALMA observations of the long wavelength dust continuum are used to estimate the gas masses in a sample of 708 star-forming (SF) galaxies at z = 0.3 to 4.5. We determine the dependence of gas masses and star formation efficiencies (SFE=SFR per unit gass mass). We find that 70 percent of the increase in SFRs of the MS is due to the increased gas masses at earlier epochs while 30 percent is due to increased efficiency of SF. For galaxies above the MS this is reversed with 70 percent of the increased SFR relative to the MS being due to elevated SFEs. Thus, the major evolution of star formation activity at early epochs is driven by increased gas masses, while the starburst activity taking galaxies above the MS is due to enhanced triggering of star formation (likely due to galactic merging). The interstellar gas peaks at z = 2 and dominates the stellar mass down to z = 1.2. Accretion rates needed to maintain continuity of the MS evolution exceed 100 Msun per yr at z > 2. The galactic gas contents are likely the driving determinant for both the rise in SF and AGN activity from z = 5 to their peak at z = 2 and subsequent fall to lower z. We suggest that for self-gravitating clouds with supersonic turbulence, cloud collisions and the filamentary structure of the clouds regulate the star formation activity.