CONSTRAINING THE LOW-MASS SLOPE OF THE STAR FORMATION SEQUENCE AT 0.5 &lt;<i>z</i>&lt; 2.5

Abstract

We constrain the slope of the star formation rate ($\\log\\Psi$) to stellar\nmass ($\\log\\mathrm{M_{\\star}}$) relation down to\n$\\log(\\mathrm{M_{\\star}/M_{\\odot}})=8.4$\n($\\log(\\mathrm{M_{\\star}/M_{\\odot}})=9.2$) at $z=0.5$ ($z=2.5$) with a\nmass-complete sample of 39,106 star-forming galaxies selected from the 3D-HST\nphotometric catalogs, using deep photometry in the CANDELS fields. For the\nfirst time, we find that the slope is dependent on stellar mass, such that it\nis steeper at low masses ($\\log\\mathrm{\\Psi}\\propto\\log\\mathrm{M_{\\star}}$)\nthan at high masses\n($\\log\\mathrm{\\Psi}\\propto(0.3-0.6)\\log\\mathrm{M_{\\star}}$). These steeper low\nmass slopes are found for three different star formation indicators: the\ncombination of the ultraviolet (UV) and infrared (IR), calibrated from a\nstacking analysis of Spitzer/MIPS 24$\\mu$m imaging; $\\beta$-corrected UV SFRs;\nand H$\\alpha$ SFRs. The normalization of the sequence evolves differently in\ndistinct mass regimes as well: for galaxies less massive than\n$\\log(\\mathrm{M_{\\star}/M_{\\odot}})&lt;10$ the specific SFR\n($\\Psi/\\mathrm{M_{\\star}}$) is observed to be roughly self-similar with\n$\\Psi/\\mathrm{M_{\\star}}\\propto(1+z)^{1.9}$, whereas more massive galaxies show\na stronger evolution with $\\Psi/\\mathrm{M_{\\star}}\\propto(1+z)^{2.2-3.5}$ for\n$\\log(\\mathrm{M_{\\star}/M_{\\odot}})=10.2-11.2$. The fact that we find a steep\nslope of the star formation sequence for the lower mass galaxies will help\nreconcile theoretical galaxy formation models with the observations. The\nresults of this study support the analytical conclusions of Leja et al. (2014).\n