The role of galaxy interactions and mergers in star formation at z ≤ 1.3:: Mid-infrared properties in the Spitzer First Look Survey

By combining the 0.12 deg(2) F814W Hubble Space Telescope (HST) and Spitzer MIPS 24 mu m imaging in the First Look Survey (FLS), we investigate the properties of interacting and merging mid-infrared bright and faint sources at 0.2 <= z <= 1.3. We find a marginally significant increase in the pair fraction for MIPS 24 mu m detected, optically selected close pairs, with a pair fraction of 0.25 +/- 0.10 at z similar to 1, in contrast to 0.11 +/- 0.08 at z similar to 0.4, while galaxies below our 24 mu m MIPS detection limit show a pair fraction consistent with zero at all redshifts. In addition, 24 mu m detected galaxies with fluxes >= 0.1 mJy are on average 5 times more likely to be in a close galaxy pair in the range 0.2 <= z <= 1.3 than galaxies below this flux limit. Using the 24 mu m flux to derive the total far-IR luminosity, we find that paired galaxies (early-stage mergers) are responsible for 27% +/- 9% of the IR luminosity density resulting from star formation at z similar to 1, while morphologically classified (late stage) mergers make up 34% +/- 11%. This implies that 61% +/- 14% of the infrared luminosity density and, in turn, similar to 40% of the star formation rate density at z similar to 1 can be attributed to galaxies at some stage of a major merger or interaction. We argue that close pairs/mergers in a LIRG/ULIRG phase become increasingly important contributors to the IR luminosity and star formation rate density of the universe at z > 0.7.