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Title:
A Spectroscopically Confirmed Excess of 24 μm Sources in a Super Galaxy Group at z = 0.37: Enhanced Dusty Star Formation Relative to the Cluster and Field Environment
Authors:
Tran, Kim-Vy H.; Saintonge, Amélie; Moustakas, John; Bai, Lei; Gonzalez, Anthony H.; Holden, Bradford P.; Zaritsky, Dennis; Kautsch, Stefan J.
Affiliation:
AA(Institute for Theoretical Physics, University of Zürich, CH-8057 Zürich, Switzerland ; George P. and Cynthia W. Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics, Texas A&M University, College Station, TX 77843, USA ; ), AB(Institute for Theoretical Physics, University of Zürich, CH-8057 Zürich, Switzerland ), AC(Center for Cosmology and Particle Physics, 4 Washington Place, New York University, New York, NY 10003, USA ; Center for Astrophysics and Space Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA ), AD(Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA ; Observatories of the Carnegie Institution of Washington, 813, Santa Barbara Street, Pasadena, CA 91101, USA ), AE(Department of Astronomy, University of Florida, Gainesville, FL 32611, USA ), AF(UCO/Lick Observatories, University of California, Santa Cruz, CA 95064, USA), AG(Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA ), AH(Department of Astronomy, University of Florida, Gainesville, FL 32611, USA )
Publication:
The Astrophysical Journal, Volume 705, Issue 1, pp. 809-820 (2009). (ApJ Homepage)
Publication Date:
11/2009
Origin:
IOP
ApJ Keywords:
galaxies: clusters: general, galaxies: clusters: individual: SG1120-1202, galaxies: evolution, galaxies: luminosity function, mass function, galaxies: starburst, infrared: galaxies
DOI:
10.1088/0004-637X/705/1/809
Bibliographic Code:
2009ApJ...705..809T

Abstract

To trace how dust-obscured star formation varies with environment, we compare the fraction of 24 μm sources in a super galaxy group to the field and a rich galaxy cluster at z ~ 0.35. We draw on multi-wavelength observations9Based on observations made with (1) The ESO telescopes at Paranal Observatories under program IDs 072.A-0367, 076.B-0362, 078.B-0409; (2) the NASA/ESA Hubble Space Telescope (GO-10499); STScI is operated by the association of Universities for Research in Astronomy, Inc. under the NASA contract NAS 5-26555; (3) 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 through an award issued by JPL/Caltech (GO-20683); (4) the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060; and (5) the Magellan 6.5 m telescope operated by OCIW. that combine Hubble, Chandra, and Spitzer imaging with extensive optical spectroscopy (>1800 redshifts) to isolate galaxies in each environment and thus ensure a uniform analysis. We focus on the four galaxy groups (σ1D = 303-580 km s-1) in supergroup 1120-12 that will merge to form a galaxy cluster comparable in mass to Coma. We find that (1) the fraction of supergroup galaxies with SFRIR >= 3 M sun yr-1 is 4 times higher than in the cluster (32% ± 5% versus 7% ± 2%); (2) the supergroup's infrared luminosity function confirms that it has a higher density of IR members compared to the cluster and includes bright IR sources (log(L IR)[erg s-1] >45) not found in galaxy clusters at z lsim 0.35; and (3) there is a strong trend of decreasing 24 μm fraction with increasing galaxy density, i.e., an infrared-density relation, not observed in the cluster. These dramatic differences are surprising because the early-type fraction in the supergroup is already as high as in clusters, i.e., the timescales for morphological transformation cannot be strongly coupled to when the star formation is completely quenched. The supergroup has a significant fraction (~17%) of luminous, low-mass (10.0 < log(M *)[M sun] < 10.6), SFRIR >= 3 M sun yr-1 members that are outside the group cores (R proj >= 0.5 Mpc) once their star formation is quenched, most will evolve into faint red galaxies. Our analysis indicates that the supergroup's 24 μm population also differs from that in the field: (1) despite the supergroup having twice the fraction of E/S0s as the field, the fraction of SFRIR >= 3 M sun yr-1 galaxies is comparable in both environments, and (2) the supergroup's IR luminosity function has a higher L*IR than that previously measured for the field.
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