December 2014 • 2014ApJ...796..135K
Abstract • The molecular gas, H2, that fuels star formation in galaxies is difficult to observe directly. As such, the ratio of L IR to L_CO^\prime is an observational estimate of the star formation rate compared with the amount of molecular gas available to form stars, which is related to the star formation efficiency and the inverse of the gas consumption timescale. We test what effect an IR luminous active galactic nucleus (AGN) has on the ratio L_IR/L_CO^\prime in a sample of 24 intermediate redshift galaxies from the 5 mJy Unbiased Spitzer Extragalactic Survey (5MUSES). We obtain new CO(1-0) observations with the Redshift Search Receiver on the Large Millimeter Telescope. We diagnose the presence and strength of an AGN using Spitzer IRS spectroscopy. We find that removing the AGN contribution to L_IR^tot results in a mean L_IR^SF/L_CO^\prime for our entire sample consistent with the mean L_IR/L_CO^\prime derived for a large sample of star forming galaxies from z ~ 0-3. We also include in our comparison the relative amount of polycyclic aromatic hydrocarbon emission for our sample and a literature sample of local and high-redshift ultra luminous infrared galaxies and find a consistent trend between L6.2/L_IR^SF and L_IR^SF/L_CO^\prime, such that small dust grain emission decreases with increasing L_IR^SF/L_CO^\prime for both local and high-redshift dusty galaxies.