Local Benchmarks for the Evolution of Major-merger Galaxies—Spitzer Observations of a K-band Selected Sample
Abstract
We present Spitzer observations for a sample of close major-merger galaxy pairs (KPAIR sample) selected from cross-matches between the Two Micron All Sky Survey and Sloan Digital Sky Survey Data Release 3. The goals are to study the star formation activity in these galaxies and to set a local bench mark for the cosmic evolution of close major mergers. The Spitzer KPAIR sample (27 pairs, 54 galaxies) includes all spectroscopically confirmed spiral-spiral (S+S) and spiral-elliptical (S+E) pairs in a parent sample that is complete for primaries brighter than K = 12.5 mag, projected separations of 5 h^(–1) kpc ≤ s ≤ 20 h^(–1) kpc, and mass ratios ≤2.5. The Spitzer data, consisting of images in seven bands (3.6, 4.5, 5.8, 8, 24, 70, 160 μm), show very diversified IR emission properties. Compared to single spiral galaxies in a control sample, only spiral galaxies in S+S pairs show significantly enhanced specific star formation rate (sSFR = SFR/M), whereas spiral galaxies in S+E pairs do not. Furthermore, the SFR enhancement of spiral galaxies in S+S pairs is highly mass-dependent. Only those with M ≳ 10^(10.5) M_☉ show significant enhancement. Relatively low-mass (M ~ 10^(10) M_☉) spirals in S+S pairs have about the same SFR/M compared to their counterparts in the control sample, while those with 10^(11) M_☉ have on average a ~3 times higher SFR/M than single spirals. There is evidence for a correlation between the global star formation activities (but not the nuclear activities) of the component galaxies in massive S+S major-merger pairs (the "Holmberg effect"). There is no significant difference in the SFR/M between the primaries and the secondaries, nor between spirals of SEP < 1 and those of SEP ≥ 1, SEP being the normalized separation parameter. The contribution of KPAIR galaxies to the cosmic SFR density in the local universe is only 1.7%, and amounts to ρ(overdot)KPAIR = 2.54 × 10^(−4) (M_☉ yr^(−1) Mpc^(−3)).
Additional Information
© 2010 American Astronomical Society. Received 2009 September 14; accepted 2010 February 17; published 2010 March 22. C.K.X. thanks David Shupe for useful discussions on the SWIRE data handling. Y.G.'s research is partly supported by grants 10833006 and 10621303 of NSF of China. W.-H.S. and Y.-W.C. acknowledge the support of the National Science Council in Taiwan under the grant NSC 97-2112-M-002-014. Constructive comments by an anonymous referee are acknowledged. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.Attached Files
Published - Xu2010p7475Astrophys_J.pdf
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Additional details
- Eprint ID
- 17938
- Resolver ID
- CaltechAUTHORS:20100412-111418037
- 10833006
- National Natural Science Foundation of China
- 10621303
- National Natural Science Foundation of China
- NSC 97-2112-M-002-014
- National Science Council (Taipei)
- Created
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2010-04-12Created from EPrint's datestamp field
- Updated
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2021-11-08Created from EPrint's last_modified field
- Caltech groups
- Infrared Processing and Analysis Center (IPAC)