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Published April 20, 2007 | Published
Journal Article Open

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 deg2 F814W Hubble Space Telescope (HST) and Spitzer MIPS 24 μm 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 μm detected, optically selected close pairs, with a pair fraction of 0.25 ± 0.10 at z ~ 1, in contrast to 0.11 ± 0.08 at z ~ 0.4, while galaxies below our 24 μm MIPS detection limit show a pair fraction consistent with zero at all redshifts. In addition, 24 μm 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 μm 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 ~ 1, while morphologically classified (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 rate density at z ~ 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.

Additional Information

© 2007 The American Astronomical Society. Received 2006 August 20; accepted 2006 December 21. We would like to thank H. Shim, M. Im, R. Chary, and C. Borys for their contributions to this work, V. Charmandaris for useful suggestions, and the anonymous referee for valuable comments that improved the clarity of the paper. This work is based on observations made with the Spitzer Observatory, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 107. Support for this work was provided in part by the Spitzer Graduate Student Fellowship program and an Ontario Graduate Scholarship in Science and Technology. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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