Top panel: gas fraction (fgas) and bottom panel: star formation efficiency (SFE) plotted as functions of distance from the MS in four bins of total stellar mass. Each point corresponds to a median value with a bootstrapped error estimate. The grey shaded area covers the range in ∆SFMS with 10% completeness in each bin.
During galactic transition towards quiescence 'it is not only the gas reservoir of a galaxy which decreases but also the efficiency with which the gas is turned into stars' - suggests a new study led by KICC researchers.
Galaxies in the observable Universe divide into two broad categories: blue, star-forming and red, quiescent. When observed across cosmic, time the distribution of galaxies shifts from the star-formation dominated to passive (quiescent) and hence these two states are interpreted as an evolutionary sequence.
Understanding the physical processes responsible for ceasing star formation is one of the long-standing questions in the area of galaxy evolution. Ultimately, galaxies may quench either due to a lack of fuel or a decrease in star formation efficiency (i.e. an increase in thedepletion time). In order to differentiate between the two possibilities one needs to measure the dense neutral gas within galaxies. However, observing the faint gas emission typically requires long exposure times on premier facilities, thus limiting the sample sizes to only a few hundred detections.
In this work led by Joanna Piotrowska, a PhD student at the Kavli, the KICC researchers use an indirect method to obtain gas mass estimates for ~62 000 local galaxies in the Sloan Digital Sky Survey which allows them to investigate the variation of gas fraction and star formation efficiency of objects on their path towards quiescence. They show that as galaxies deviate from the star-forming Main Sequence (a tight relation between the galaxy stellar mass and star formation rate) it is not only the gas reservoir of a galaxy which decreases but also the efficiency with which the gas is turned into stars as shown in the figure at the above of the page.
These results call for a better understanding of the physical processes driving the decrease in star formation efficiency, which has received relatively little attention in the theory of quenching until now.
You can freely access the article at this link or with a subscription in the MNRAS Letters here.
