The Role of Galaxy Interactions and Mergers in Star Formation atz ≤ 1.3: Mid‐Infrared Properties in theSpitzerFirst Look Survey

By combining the 0.12 square degree F814W Hubble Space Telescope (HST) andSpitzer MIPS 24 micron imaging in the First Look Survey (FLS), we investigatethe properties of interacting and merging Mid-Infrared bright and faint sourcesat 0.2< z <1.3. We find a marginally significant increase in the pair fractionfor MIPS 24 micron detected, optically selected close pairs, pairfraction=0.25+/-0.10 at z~1, in contrast to 0.11+/-0.08 at z~0.4, whilegalaxies below our 24 micron MIPS detection limit show a pair fractionconsistent with zero at all redshifts. Additionally, 24 micron detectedgalaxies with fluxes >0.1mJy are on average five times more likely to be in aclose galaxy pair between 0.2< z <1.3 than galaxies below this flux limit.Using the 24 micron flux to derive the total Far-IR luminosity we find thatpaired galaxies (early stage mergers) are responsible for 27% +/-9% of the IRluminosity density resulting from star formation at z~1 while morphologicallyclassified (late stage) mergers make up 34%+/-11%. This implies that 61%+/-14%of the infrared luminosity density and in turn ~40% of the star formation ratedensity at z~1 can be attributed to galaxies at some stage of a major merger orinteraction. We argue that, close pairs/mergers in a LIRG/ULIRG phase becomeincreasingly important contributers to the IR luminosity and star formationrate density of the Universe at z>0.7.Comment: accepted for publication in ApJ, 10 page