A far-infrared characterization of 24 μm selected galaxies at 0 < z < 2.5 using stacking at 70 μm and 160 μm in the cosmos field

Abstract

We present a study of the average properties of luminous infrared galaxies detected directly at 24 μm in the COSMOS field using a median stacking analysis at 70 μm and 160 μm. Over 35,000 sources spanning 0 ≤ z ≤ 3 and 0.06mJy ≤S 24 ≤ 3.0mJy are stacked, divided into bins of both photometric redshift and 24 μm flux. We find no correlation of S 70/S 24 flux density ratio with S 24, but find that galaxies with higher S 24 have a lower S 160/S 24 flux density ratio. These observed ratios suggest that 24 μm selected galaxies have warmer spectral energy distributions (SEDs) at higher mid-IR fluxes, and therefore have a possible higher fraction of active galactic nuclei. Comparisons of the average S 70/S 24 and S 160/S 24 colors with various empirical templates and theoretical models show that the galaxies detected at 24 μm are consistent with "normal" star-forming galaxies and warm mid-IR galaxies such as Mrk 231, but inconsistent with heavily obscured galaxies such as Arp 220. We perform a χ2 analysis to determine best-fit galactic model SEDs and total IR luminosities for each of our bins. We compare our results to previous methods of estimating L IR and find that previous methods show considerable agreement over the full redshift range, except for the brightest S 24 sources, where they overpredict the bolometric IR luminosity at high redshift, most likely due to their warmer dust SED. We present a table that can be used as a more accurate and robust method for estimating bolometric infrared luminosity from 24 μm flux densities. © 2010. The American Astronomical Society. All rights reserved..