Infrared Properties of Close Pairs of Galaxies

Creators: Geller, Margaret J.; Kenyon, Scott J.; Barton, Elizabeth J.; Jarrett, Thomas H.; Kewley, Lisa J.

Abstract

We discuss spectroscopy and IR photometry for a complete sample of ~800 galaxies in close pairs objectively selected from the second Center for Astrophysics redshift survey. We use the Two Micron All Sky Survey to compare near-IR color-color diagrams for our sample with the Nearby Field Galaxy Sample and with a set of IRAS flux-limited pairs from Surace and coworkers. We construct a basic statistical model to explore the physical sources of the substantial differences among these samples. The model explains the spread of near-IR colors and is consistent with a picture in which central star formation is triggered by the galaxy-galaxy interaction before a merger occurs. For 160 galaxies we report new, deep JHK photometry within our spectroscopic aperture, and we use the combined spectroscopic and photometric data to explore the physical conditions in the central bursts. We find a set of objects with H - K ≥ 0.45 and with a large F_(FIR)/F_H. We interpret the very red H - K colors as evidence for 600-1000 K dust within compact star-forming regions, perhaps similar to super star clusters identified in individual well-studied interacting galaxies. The galaxies in our sample are candidate "hidden" bursts or, possibly, "hidden" active galactic nuclei. Over the entire pair sample, both spectroscopic and photometric data show that the specific star formation rate decreases with the projected separation of the pair. The data suggest that the near-IR color-color diagram is also a function of the projected separation; all of the objects with central near-IR colors indicative of bursts of star formation lie at small projected separation.

Additional Information

© 2006 The American Astronomical Society. Received 2006 April 13; accepted 2006 August 1. We thank Jason Surace for providing early versions of the computer-readable tables from SSM04. We thank the anonymous referee for comments that prompted several important clarifications. This paper uses data from the Infrared Astronomical Satellite, a joint project of the Netherlands Agency for Aerospace Programs, theUS National Aeronautics and Space Administration, and the UK Science and Engineering Research Council. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This research has made use of the NASA/ IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

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