Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 430, Issue 4, Pages 3128-3141Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/sts546
Keywords
galaxies: active; galaxies: interactions; galaxies: star formation; infrared: galaxies
Categories
Funding
- NSERC
- Alfred P. Sloan Foundation
- National Science Foundation
- U.S. Department of Energy
- National Aeronautics and Space Administration
- Japanese Monbukagakusho
- Max Planck Society
- Higher Education Funding Council for England
- American Museum of Natural History
- Astrophysical Institute Potsdam
- University of Basel
- University of Cambridge
- Western Reserve University
- University of Chicago
- Drexel University
- Fermilab
- Institute for Advanced Study
- Joint Institute for Nuclear Astrophysics
- Kavli Institute for Particle Astrophysics and Cosmology
- Korean Scientist Group
- Chinese Academy of Sciences (LAMOST)
- Los Alamos National Laboratory
- Max-Planck-Institute for Astronomy (MPIA)
- Max-Planck-Institute for Astrophysics (MPA)
- New Mexico State University
- Ohio State University
- University of Pittsburgh
- University of Portsmouth
- Princeton University
- United States Naval Observatory
- University of Washington
- Japan Participation Group
- Johns Hopkins University
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We use a sample of 9397 low-redshift (z <= 0.1) galaxies with a close companion to investigate the connection between mergers and luminous infrared (IR) galaxies (LIRGs). The pairs are selected from the Sloan Digital Sky Survey (SDSS) and have projected separations r(p) <= 80 h(70)(-1) kpc, relative velocities Delta V <= 300 km s(-1) and stellar mass ratios within a factor of 1:10. A control sample consisting of four galaxies per pair galaxy is constructed by simultaneously matching in stellar mass, redshift and environment to galaxies with no close companion. The IR luminosities (L-IR) of galaxies in the pair and control samples are determined from the SDSS - Infrared Astronomical Satellite (IRAS) matched catalogue of Hwang et al. Over the redshift range of our pairs sample, the IRAS matches are complete to LIRG luminosities (L-IR >= 10(11) L-circle dot), allowing us to investigate the connection between mergers and luminous IR galaxies. We find a trend for increasing LIRG fraction towards smaller pair separations, peaking at a factor of similar to 5-10 above the median control fraction at the smallest separations (r(p) < 20 h(70)(-1) kpc), but remaining elevated by a factor similar to 2-3 even out to 80 h(70)(-1) kpc (the widest separations in our sample). LIRG pairs predominantly have high star formation rates (SFRs), high extinction and are found in relatively low-density environments, relative to the full pairs sample. We also find that LIRGs are most likely to be found in high-mass galaxies which have an approximately equal-mass companion. We confirm the results of previous studies that both the active galactic nucleus (AGN) fraction and merger fraction increase strongly as a function of IR luminosity. About 7 per cent of LIRGs are associated with major mergers, as defined within the criteria and mass completion of our sample. Finally, we quantify an SFR offset (Delta SFR) as the enhancement (or decrement) relative to star-forming galaxies of the same mass and redshift. We demonstrate that there is a clear connection between the Delta SFR and the classification of a galaxy as a LIRG that is mass dependent. Most of the LIRGs in our merger sample are relatively high-mass galaxies (log (M-star/M-circle dot) > 10.5), likely because the SFR enhancement required to produce LIRG luminosities is more modest than at low masses. The Delta SFR offers a redshift-independent metric for the identification of the galaxies with the most enhanced star-forming rates that does not rely on fixed L-IR boundaries.
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