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The Emission-line Spectra of Major Mergers: Evidence for Shocked Outflows

Soto, Kurt T. and Martin, C. L. and Prescott, M. K. M. and Armus, L. (2012) The Emission-line Spectra of Major Mergers: Evidence for Shocked Outflows. Astrophysical Journal, 757 (1). Art. No. 86. ISSN 0004-637X. doi:10.1088/0004-637X/757/1/86.

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Using a spectral decomposition technique, we investigate the physical origin of the high-velocity emission-line gas in a sample of 39 gas-rich, ultraluminous infrared galaxy mergers. Regions with shock-like excitation were identified in two kinematically distinct regimes, characterized by broad (σ > 150 km s^(–1)) and narrow linewidths (σ ≤ 150 km s^(–1)). Here, we investigate the physical origin of the broad emission, which we show is predominantly excited by shocks with velocities of 200-300 km s^(–1). Considering the large amount of extinction in these galaxies, the blueshift of the broad emission suggests an origin on the near side of the galaxy and therefore an interpretation as a galactic outflow. The large spatial extent of the broad, shocked emission component is generally inconsistent with an origin in the narrow-line region of an active galactic nucleus. The kinetic energy in the mass loss as well as the luminosity of the emission lines is consistent with the fraction of the supernova energy attributed to these mechanisms by shocked stellar winds. Since some shocks can be recognized in moderately high resolution, integrated spectra of nearby ultraluminous starbursts, the spectral fitting technique introduced in Soto & Martin may therefore be used to improve the accuracy of the physical properties measured for high-redshift galaxies from their (observed frame) infrared spectra.

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Armus, L.0000-0003-3498-2973
Additional Information:© 2012 American Astronomical Society. Received 2012 April 10; accepted 2012 July 29; published 2012 September 6. The authors thank Kristian Finlator, Nicolas Bouch´e, Alaina Henry, Vardha Bennert, Tommaso Treu, and Omer Blaes for illuminating discussions. This work was supported by the National Science Foundation under contracts AST-0808161 and AST-1109288 and the Department of Education through the Graduate Assistance in Areas of National Need program. A portion of this work was completed at the Aspen Center for Physics. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Facility: Keck:II The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.
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Department of Education Graduate Assistance in Areas of National Need programUNSPECIFIED
Subject Keywords:galaxies: active; galaxies: evolution; galaxies: formation; galaxies: starburst
Issue or Number:1
Record Number:CaltechAUTHORS:20121029-103812452
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Official Citation:The Emission-line Spectra of Major Mergers: Evidence for Shocked Outflows Kurt T. Soto et al. 2012 ApJ 757 86
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35150
Deposited By: Jason Perez
Deposited On:30 Oct 2012 19:48
Last Modified:09 Nov 2021 23:13

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