A SPECTROSCOPICALLY CONFIRMED EXCESS OF 24 mum SOURCES IN A SUPER GALAXY GROUP AT z = 0.37: ENHANCED DUSTY STAR FORMATION RELATIVE TO THE CLUSTER AND FIELD ENVIRONMENT

Journal Article · Sun Nov 01 00:00:00 EDT 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/705/1/809· OSTI ID:21378300

Tran, Kim-Vy H; Saintonge, Amelie ^[1]; Moustakas, John ^[2]; Bai, Lei; Zaritsky, Dennis ^[3]; Gonzalez, Anthony H; Kautsch, Stefan J ^[4]

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1. Institute for Theoretical Physics, University of Zuerich, CH-8057 Zuerich (Switzerland)
2. Center for Cosmology and Particle Physics, 4 Washington Place, New York University, New York, NY 10003 (United States)
3. Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)
4. Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States)

To trace how dust-obscured star formation varies with environment, we compare the fraction of 24 mum sources in a super galaxy group to the field and a rich galaxy cluster at z approx 0.35. We draw on multi-wavelength observations{sup 9}Based 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 (sigma{sub 1D} = 303-580 km s{sup -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 SFR{sub IR} >= 3 M {sub sun} yr{sup -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 {sub IR})[erg s{sup -1}] >45) not found in galaxy clusters at z approx< 0.35; and (3) there is a strong trend of decreasing 24 mum 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 (approx17%) of luminous, low-mass (10.0 < log(M {sub *})[M {sub sun}] < 10.6), SFR{sub IR} >= 3 M {sub sun} yr{sup -1} members that are outside the group cores (R {sub 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 mum 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 SFR{sub IR} >= 3 M {sub sun} yr{sup -1} galaxies is comparable in both environments, and (2) the supergroup's IR luminosity function has a higher L*{sub IR} than that previously measured for the field.

• OSTI ID: 21378300
• Journal Information: Astrophysical Journal, Vol. 705, Issue 1; Other Information: DOI: 10.1088/0004-637X/705/1/809; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ASTRONOMY
ASTROPHYSICS
DENSITY
DUSTS
ESA
GALACTIC EVOLUTION
GALAXIES
GALAXY CLUSTERS
LUMINOSITY
NASA
RED SHIFT
SPECTROSCOPY
STARS
TELESCOPES
EVOLUTION
INTERNATIONAL ORGANIZATIONS
NATIONAL ORGANIZATIONS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
PHYSICS
US ORGANIZATIONS