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Published July 2010 | Published
Journal Article Open

The Buried Starburst in the Interacting Galaxy II Zw 096 as Revealed by the Spitzer Space Telescope


An analysis of data from the Spitzer Space Telescope, Hubble Space Telescope, Chandra X-ray Observatory, and AKARI Infrared Astronomy Satellite is presented for the z = 0.036 merging galaxy system II Zw 096 (CGCG 448-020). Because II Zw 096 has an infrared luminosity of log(L_(IR)/L_☉) = 11.94, it is classified as a Luminous Infrared Galaxy (LIRG), and was observed as part of the Great Observatories All-sky LIRG Survey (GOALS). The Spitzer data suggest that 80% of the total infrared luminosity comes from an extremely compact, red source not associated with the nuclei of the merging galaxies. The Spitzer mid-infrared spectra indicate no high-ionization lines from a buried active galactic nucleus in this source. The strong detection of the 3.3 μm and 6.2 μm polycyclic aromatic hydrocarbon emission features in the AKARI and Spitzer spectra also implies that the energy source of II Zw 096 is a starburst. Based on Spitzer infrared imaging and AKARI near-infrared spectroscopy, the star formation rate is estimated to be 120 M_☉ yr^(-1) and >45 M_☉ yr^(-1), respectively. Finally, the high-resolution B-, I-, and H-band images show many star clusters in the interacting system. The colors of these clusters suggest at least two populations—one with an age of 1-5 Myr and one with an age of 20-500 Myr, reddened by 0-2 mag of visual extinction. The masses of these clusters span a range between 10^6 and 10^8 M_☉. This starburst source is reminiscent of the extranuclear starburst seen in NGC 4038/9 (the Antennae Galaxies) and Arp 299 but approximately an order of magnitude more luminous than the Antennae. The source is remarkable in that the off-nuclear infrared luminosity dominates the entire system.

Additional Information

© 2010 American Astronomical Society. Received 2009 November 9; accepted 2010 April 19; published 2010 May 20. We thank J. Goldader and S. Satyapal for many helpful suggestions. The authors also thank an anonymous referee for suggestions which improved the manuscript. The Spitzer Space Telescope is operated by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407. This research has made use of the NASA/IPAC Extragalactic Database (NED) and the Infrared Science Archive (IRSA) which are operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Hanae Inami thanks the Spitzer Visiting Graduate Student Fellowship (from 2008 September to 2009 February) and Grant-in-Aid for Japan Society for the Promotion of Science (JSPS) Fellows (21-969) for supporting this work. Facilities: Akari, CXO, HST, Spitzer

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