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Publication Details
AFRICAN RESEARCH NEXUS
SHINING A SPOTLIGHT ON AFRICAN RESEARCH
earth and planetary sciences
Enhanced warm H
2
emission in the compact group mid-infrared "green valley"
Astrophysical Journal, Volume 765, No. 2, Article 93, Year 2013
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Description
We present results from a Spitzer mid-infrared spectroscopy study of a sample of 74 galaxies located in 23 Hickson Compact Groups (HCGs), chosen to be at a dynamically active stage of H I depletion. We find evidence for enhanced warm H2 emission (i.e., above that associated with UV excitation in star-forming regions) in 14 galaxies (∼20%), with 8 galaxies having extreme values of L(H2 S(0)-S(3))/L(7.7 μm polycyclic aromatic hydrocarbon), in excess of 0.07. Such emission has been seen previously in the compact group HCG 92 (Stephan's Quintet), and was shown to be associated with the dissipation of mechanical energy associated with a large-scale shock caused when one group member collided, at high velocity, with tidal debris in the intragroup medium. Similarly, shock excitation or turbulent heating is likely responsible for the enhanced H2 emission in the compact group galaxies, since other sources of heating (UV or X-ray excitation from star formation or active galactic nuclei) are insufficient to account for the observed emission. The group galaxies fall predominantly in a region of mid-infrared color-color space identified by previous studies as being connected to rapid transformations in HCG galaxy evolution. Furthermore, the majority of H2-enhanced galaxies lie in the optical "green valley" between the blue cloud and red sequence, and are primarily early-type disk systems. We suggest that H2-enhanced systems may represent a specific phase in the evolution of galaxies in dense environments and provide new insight into mechanisms which transform galaxies onto the optical red sequence. © 2013. The American Astronomical Society. All rights reserved.
Authors & Co-Authors
Cluver, Michelle E.
United States, Pasadena
Spitzer Science Center
Australia
Australian Astronomical Observatory
Appleton, Philip N.
United States, Pasadena
California Institute of Technology
Ogle, Patrick Michael
United States, Pasadena
Spitzer Science Center
Jarrett, Thomas H.
South Africa, Cape Town
University of Cape Town
Rasmussen, J.
Denmark, Copenhagen
Niels Bohr Institutet
Lisenfeld, Ute
Spain, Granada
Universidad de Granada, Facultad de Ciencias
Guillard, Pierre
United States, Pasadena
Spitzer Science Center
Verdes-Montenegro, Lourdes
Spain, Granada
Instituto de Astrofísica de Andalucía - Csic
Antonucci, R.
United States, Santa Barbara
University of California, Santa Barbara
Bitsakis, Theodoros
Greece, Rethymnon
University of Crete
Charmandaris, V.
Greece, Rethymnon
University of Crete
Greece, Heraklion
Institute of Electronic Structure and Laser of the Foundation for Research and Technology-hellas
France, Paris
L'observatoire de Paris
Boulanger, Franc¸ois
France, Orsay
Institut D'astrophysique Spatiale
Egami, Eiichi E.
United States, Tucson
The University of Arizona
Xu, Cong Kevin
Australia
Australian Astronomical Observatory
Yun, Minsu
United States, Amherst
University of Massachusetts Amherst
Statistics
Citations: 45
Authors: 15
Affiliations: 14
Identifiers
Doi:
10.1088/0004-637X/765/2/93
ISSN:
0004637X
e-ISSN:
15384357
Research Areas
Environmental