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Composite Spectra in Merging U/LIRGs Caused by Shocks

Rich, J. A. and Kewley, L. J. and Dopita, M. A. (2014) Composite Spectra in Merging U/LIRGs Caused by Shocks. Astrophysical Journal Letters, 781 (1). Art. No. L12. ISSN 2041-8205. doi:10.1088/2041-8205/781/1/L12.

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We present a key result from our optical integral field spectroscopic survey of 27 nearby ultraluminous and luminous infrared galaxies (U/LIRGs) from the Great Observatory All-Sky LIRG Survey. Using spatially resolved multi-component emission line fitting to trace the emission line ratios and velocity dispersion of the ionized gas, we quantify for the first time the widespread shock ionization in gas-rich merging U/LIRGs. Our results show a fractional contribution to the total observed Hα flux from radiative shocks increasing from a few percent during early merger stages to upward of 60% of the observed optical emission line flux in late-stage mergers. We compare our resolved spectroscopy to nuclear spectra and find that 3/4 of the galaxies in our sample that would be classified as "composite" based on optical spectroscopy are primarily characterized by a combination of star formation and merger-driven shocks. Our results have important implications for the interpretation of "composite" rest-frame optical spectra of U/LIRGs as starburst+active galactic nucleus (AGN), as the shock emission combined with star formation can mimic "composite" optical spectra in the absence of any contribution from an AGN.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Rich, J. A.0000-0002-5807-5078
Kewley, L. J.0000-0001-8152-3943
Additional Information:© 2014 American Astronomical Society. Received 2013 September 8; accepted 2013 October 7; published 2014 January 6. We thank the referee for a careful reading of the Letter and insightful comments which improved the manuscript. The authors acknowledge ARC support under Discovery project DP0984657. 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. This research has also made use of NASA’s Astrophysics Data System, and of SAOImage DS9 (Joye & Mandel 2003), developed by the Smithsonian Astrophysical Observatory.
Funding AgencyGrant Number
Australian Research CouncilDP0984657
Subject Keywords:galaxies: active; galaxies: evolution; galaxies: ISM
Issue or Number:1
Record Number:CaltechAUTHORS:20140210-115809860
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Official Citation:Composite Spectra in Merging U/LIRGs Caused by Shocks J. A. Rich et al. 2014 ApJ 781 L12
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:43747
Deposited By: Jason Perez
Deposited On:10 Feb 2014 22:04
Last Modified:10 Nov 2021 16:42

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