Optical Morphology Evolution of Infrared Luminous Galaxies in Goods-n

We combine optical morphologies and photometry from HST, redshifts from Keck, and mid-infrared luminosities from Spitzer for an optically selected sample of ∼ 800 galaxies in GOODS-N to track morphology evolution of infrared luminous galaxies (LIRGs) since redshift z = 1. We find a 50% decline in the number of LIRGs from z ∼ 1 to lower redshift, in agreement with previous studies. In addition, there is evidence for a morphological evolution of the populations of LIRGs. Above z = 0.5, roughly half of all LIRGs are spiral, the peculiar/irregular to spiral ratio is ∼ 0.7, and both classes span a similar range of LIR and MB. At low-z, spirals account for one-third of LIRGs, the peculiar to spiral fraction rises to 1.3, and for a given MB spirals tend to have lower IR luminosity than peculiars. Only a few percent of LIRGs at any redshift are red early-type galaxies. For blue galaxies (U − B < 0.2), MB is well correlated with log(LIR) with an RMS scatter (about a bivariate linear fit) of ∼ 0.25 dex in IR luminosity. Among blue galaxies that are brighter than MB = −21, 75% are LIRGs, regardless of redshift. These results can be explained by a scenario in which at high-z, most large spirals experience an elevated star formation rate as LIRGs. Gas consumption results in a decline of LIRGs, especially in spirals, to lower redshifts. Subject headings: galaxies: evolution – infrared: galaxies