A MULTIWAVELENGTH STUDY OF A SAMPLE OF 70 {mu}m SELECTED GALAXIES IN THE COSMOS FIELD. II. THE ROLE OF MERGERS IN GALAXY EVOLUTION

Journal Article · Mon Sep 20 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/721/1/98· OSTI ID:21464879

Kartaltepe, Jeyhan S; Sanders, D B; Le Floc'h, E ^[1]; Frayer, D T ^[2]; Aussel, H ^[3]; Arnouts, S ^[4]; Ilbert, O; Cassata, P; Le Fevre, O ^[5]; Salvato, M; Scoville, N Z; Capak, P ^[6]; Surace, J; Yan, L ^[7]; Caputi, K; Carollo, C M; Lilly, S ^[8]; Civano, F ^[9]; Hasinger, G ^[10]

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1. Institute for Astronomy, 2680 Woodlawn Drive, University of Hawaii, Honolulu, HI 96822 (United States)
2. Infrared Processing and Analysis Center, California Institute of Technology 100-22, Pasadena, CA 91125 (United States)
3. CNRS, AIM-Unite Mixte de Recherche CEA-CNRS-Universite Paris VII-UMR 7158, F-91191 Gif-sur-Yvette (France)
4. Canada-France-Hawaii Telescope Corporation, 65-1238 Mamalahoa Hwy, Kamuela, HI 96743 (United States)
5. Laboratoire d'Astrophysique de Marseille, BP 8, Traverse du Siphon, 13376 Marseille Cedex 12 (France)
6. California Institute of Technology, MC 105-24, 1200 East California Boulevard, Pasadena, CA 91125 (United States)
7. Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125 (United States)
8. Department of Physics, ETH Zurich, CH-8093 Zurich (Switzerland)
9. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
10. Max Planck Institut fuer Extraterrestrische Physik, D-85478 Garching (Germany)

We analyze the morphological properties of a large sample of 1503 70 {mu}m selected galaxies in the COSMOS field spanning the redshift range 0.01 < z < 3.5 with a median redshift of 0.5 and an infrared luminosity range of 10{sup 8} < L{sub IR}(8 - 1000 {mu}m)< 10{sup 14} L{sub sun} with a median luminosity of 10{sup 11.4} L{sub sun}. In general, these galaxies are massive, with a stellar mass range of 10{sup 10}-10{sup 12} M{sub sun}, and luminous, with -25 < M{sub K} < -20. We find a strong correlation between the fraction of major mergers and L{sub IR}, with the fraction at the highest luminosity (L{sub IR} > 10{sup 12} L{sub sun}) being up to {approx}50%. We also find that the fraction of spirals drops dramatically with L{sub IR}. Minor mergers likely play a role in boosting the infrared luminosity for sources with low luminosities (L{sub IR} < 10{sup 11.5} L{sub sun}). The precise fraction of mergers in any given L{sub IR} bin varies by redshift due to sources at z > 1 being difficult to classify and subject to the effects of bandpass shifting; therefore, these numbers can only be considered lower limits. At z < 1, where the morphological classifications are most robust, major mergers clearly dominate the ULIRG population ({approx}50%-80%) and are important for the LIRG population ({approx}25%-40%). At z > 1, the fraction of major mergers is lower, but is at least 30%-40% for ULIRGs. In a comparison of our visual classifications with several automated classification techniques we find general agreement; however, the fraction of identified mergers is underestimated due to automated classification methods being sensitive to only certain timescales of a major merger. Although the general morphological trends agree with what has been observed for local (U)LIRGs, the fraction of major mergers is slightly lower than seen locally. This is in part due to the difficulty of identifying merger signatures at high redshift. The distribution of the U - V color of the galaxies in our sample peaks in the green valley ((U - V) = 1.1) with a large spread at bluer and redder colors and with the major mergers peaking more strongly in the green valley than the rest of the morphological classes. We argue that, given the number of major gas-rich mergers observed and the relatively short timescale that they would be observable in the (U)LIRG phase, it is plausible for the observed red sequence of massive ellipticals (<10{sup 12} M{sub sun}) to have been formed entirely by gas-rich major mergers.

• OSTI ID: 21464879
• Journal Information: Astrophysical Journal, Vol. 721, Issue 1; Other Information: DOI: 10.1088/0004-637X/721/1/98; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
COLOR
COSMOLOGY
GALACTIC EVOLUTION
GALAXIES
LUMINOSITY
RED SHIFT
UNIVERSE
EVOLUTION
OPTICAL PROPERTIES
ORGANOLEPTIC PROPERTIES
PHYSICAL PROPERTIES