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High-Resolution Mid-Infrared Spectroscopy of Ultraluminous Infrared Galaxies

Farrah, D. and Bernard-Salas, J. and Spoon, H. W. W. and Soifer, B. T. and Armus, L. and Brandl, B. and Charmandaris, V. and Desai, V. and Higdon, S. and Devost, D. and Houck, J. (2007) High-Resolution Mid-Infrared Spectroscopy of Ultraluminous Infrared Galaxies. Astrophysical Journal, 667 (1). pp. 149-169. ISSN 0004-637X. doi:10.1086/520834.

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We present R ~ 600, 10-37 μm spectra of 53 ultraluminous infrared galaxies (ULIRGs), taken using the Infrared Spectrograph on board Spitzer. The spectra show fine-structure emission lines of neon, oxygen, sulfur, silicon, argon, chlorine, iron, and phosphorous; molecular hydrogen lines, and C_2H_2, HCN, and OH^- absorption features. We employ diagnostics based on the fine-structure lines, the polycyclic aromatic hydrocarbon (PAH) features and the 9.7 μm silicate absorption feature, to show that the infrared emission from most ULIRGs is powered mostly by star formation, with only ~20% of ULIRGs hosting an AGN with a greater IR luminosity than the starburst. The detection of [Ne V] λ14.32 in just under half the sample, however, implies that an AGN contributes significantly to the mid-IR flux in ~42% of ULIRGs. The starbursts and AGNs in ULIRGs appear more extincted, and for the starbursts more compact than those in lower luminosity systems. The excitations and electron densities in the narrow-line regions of ULIRGs appear comparable to those of starbursts with L ≾ 10^(11.5) L_⊙, although the NLR gas in ULIRGs may be more dense. We show that the [Ne II] λ12.81 + [Ne III] λ15.56 luminosity correlates with both infrared luminosity and the luminosity of the 6.2 and 11.2 μm PAH features, and derive a calibration between PAH luminosity and star formation rate. Finally, we show that ULIRGs with silicate absorption strengths Ssil of 0.8 ≾ S_(sil) ≾ 2.4 are likely to be powered mainly by star formation, but that ULIRGs with S_(sil) ≾ 0.8, and possibly those with S_(sil) ≳ 2.4, contain an IR-luminous AGN.

Item Type:Article
Related URLs:
URLURL TypeDescription DOIArticle
Farrah, D.0000-0003-1748-2010
Bernard-Salas, J.0000-0002-8452-8675
Spoon, H. W. W.0000-0002-8712-369X
Armus, L.0000-0003-3498-2973
Charmandaris, V.0000-0002-2688-1956
Desai, V.0000-0002-1340-0543
Higdon, S.0000-0002-4021-7453
Additional Information:© 2007 The American Astronomical Society. Received 2007 March 24; accepted 2007 May 30. We thank Xander Tielens and Javier Goicoechea for advice on OH- absorption features, and the referee for a very helpful report. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA. This research has made extensive use of the NASA/ IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Subject Keywords:galaxies : active; galaxies : evolution; galaxies : starburst; infrared : galaxies
Issue or Number:1
Record Number:CaltechAUTHORS:20100222-090606361
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Official Citation:High-Resolution Mid-Infrared Spectroscopy of Ultraluminous Infrared Galaxies D. Farrah, J. Bernard-Salas, H. W. W. Spoon, B. T. Soifer, L. Armus, B. Brandl, V. Charmandaris, V. Desai, S. Higdon, D. Devost, and J. Houck 2007 ApJ 667 149-169 doi: 10.1086/520834
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:17542
Deposited By: Tony Diaz
Deposited On:22 Feb 2010 17:31
Last Modified:08 Nov 2021 23:36

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