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Detection of Powerful Mid-IR H_2 Emission in the Bridge between the Taffy Galaxies

Peterson, B. W. and Appleton, P. N. and Helou, G. and Guillard, P. and Jarrett, T. H. and Cluver, M. E. and Ogle, P. and Struck, C. and Boulanger, F. (2012) Detection of Powerful Mid-IR H_2 Emission in the Bridge between the Taffy Galaxies. Astrophysical Journal, 751 (1). p. 11. ISSN 0004-637X. doi:10.1088/0004-637X/751/1/11.

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We report the detection of strong, resolved emission from warm H_2 in the Taffy galaxies and bridge. Relative to the continuum and faint polyclic aromatic hydrocarbon (PAH) emission, the H_2 emission is the strongest in the connecting bridge, approaching L(H_2)/L(PAH 8 μm) = 0.1 between the two galaxies, where the purely rotational lines of H_2 dominate the mid-infrared spectrum in a way very reminiscent of the group-wide shock in the interacting group Stephan's Quintet (SQ). The surface brightness in the 0-0 S(0) and S(1) H_2 lines in the bridge is more than twice that observed at the center of the SQ shock. We observe a warm H2 mass of 4.2 × 10^8 M_☉ in the bridge, but taking into account the unobserved bridge area, the total warm mass is likely to be twice this value. We use excitation diagrams to characterize the warm molecular gas, finding an average surface mass of ~5 × 10^6 M_☉ kpc^(–2) and typical excitation temperatures of 150-175 K. H_2 emission is also seen in the galaxy disks, although there the emission is more consistent with normal star-forming galaxies. We investigate several possible heating mechanisms for the bridge gas but favor the conversion of kinetic energy from the head-on collision via turbulence and shocks as the main heating source. Since the cooling time for the warm H_2 is short (~5000 yr), shocks must be permeating the molecular gas in the bridge region in order to continue heating the H_2.

Item Type:Article
Related URLs:
URLURL TypeDescription
Appleton, P. N.0000-0002-7607-8766
Helou, G.0000-0003-3367-3415
Guillard, P.0000-0002-2421-1350
Jarrett, T. H.0000-0002-4939-734X
Cluver, M. E.0000-0002-9871-6490
Ogle, P.0000-0002-3471-981X
Struck, C.0000-0002-6490-2156
Additional Information:© 2012 American Astronomical Society. Received 2011 January 21; accepted 2012 March 11; published 2012 April 30. B.W.P. thanks the IPAC Visiting Graduate Student Fellowship (from 2009 September to 2010 March) for supporting this work. We also thank Jim Condon for providing a digital copy of the 20 cm radio data and the anonymous referee for many insightful comments that greatly improved this manuscript. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory (JPL), California Institute of Technology (Caltech) under NASA contract. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Facility: Spitzer
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
IPAC Visiting Graduate Student FellowshipUNSPECIFIED
Subject Keywords:galaxies: individual (UGC 12914, UGC 12915); galaxies: interactions; intergalactic medium
Issue or Number:1
Record Number:CaltechAUTHORS:20120605-123347820
Persistent URL:
Official Citation:Detection of Powerful Mid-IR H2 Emission in the Bridge between the Taffy Galaxies B. W. Peterson et al. 2012 ApJ 751 11
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:31817
Deposited By: Jason Perez
Deposited On:06 Jun 2012 19:55
Last Modified:09 Nov 2021 20:01

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