The bending of the star-forming main sequence traces the cold- to hot-accretion transition mass over 0<z<4

Abstract

We analyse measurements of the evolving stellar mass (M0) at which the bending of the star-forming main sequence (MS) occurs over 0 1.4 (for which we propose a revision in agreement with latest simulations). We hence argue that the MS bending is primarily due to the lessening of cold-accretion causing a reduction in available cold gas in galaxies and supports predictions of gas feeding theory. In particular, the rapidly rising M0 with redshift at z>1 is confirming evidence for the cold-streams scenario. In this picture, a progressive fueling reduction rather than its sudden suppression in halos more massive than Mshock/Mstream produces a nearly constant star-formation rate in galaxies with stellar masses larger than M0, and not their quenching, for which other physical processes are thus required. Compared to the knee M* in the stellar mass function of galaxies, M0 is significantly lower at z<1.5, and higher at z>2, suggesting that the imprint of gas deprivation on the distribution of galaxy masses happened at early times (z>1.5-2). The typical mass at which galaxies inside the MS become bulge-dominated evolves differently from M0, consistent with the idea that bulge-formation is a distinct process from the phasing-out of cold-accretion.