Star Formation Efficiency at Intermediate Redshift

TL;DR

This study investigates the evolution of star formation efficiency and gas content in ultra-luminous infrared galaxies between redshifts 0.2 and 1, revealing significant changes and a turning point around z=0.35, with implications for cosmic star formation history.

Contribution

It provides new observational evidence of the evolution of gas fraction and SFE in ULIRGs at intermediate redshifts, highlighting a turning point and comparing results with cosmic trends.

Findings

Gas fraction and SFE increase with redshift in ULIRGs.

A turning point in gas properties occurs around z=0.35.

ULIRGs at 0.2<z<1 have higher SFE and gas fraction than local counterparts.

Abstract

Star formation is evolving very fast in the second half of the Universe, and it is yet unclear whether this is due to evolving gas content, or evolving star formation efficiency (SFE). We have carried out a survey of ultra-luminous galaxies (ULIRG) between z=0.2 and 1, to check the gas fraction in this domain of redshift which is still poorly known. Our survey with the IRAM-30m detected 33 galaxies out of 69, and we derive a significant evolution of both the gas fraction and SFE of ULIRGs over the whole period, and in particular a turning point around z=0.35. The result is sensitive to the CO-to-H2, conversion factor adopted, and both gas fraction and SFE have comparable evolution, when we adopt the low starburst conversion factor of \alpha =0.8 Mo/(K km/s pc^2). Adopting a higher \alpha will increase the role of the gas fraction. Using \alpha =0.8, the SFE and the gas fraction for z=0.2-1.0 ULIRGs are found to be significantly higher, by a factor 3, than for local ULIRGs, and are comparable to high redshift ones. We compare this evolution to the expected cosmic H2 abundance and the cosmic star formation history.