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PAH Emission from Ultraluminous Infrared Galaxies

Desai, V. and Armus, L. and Spoon, H. W. W. and Charmandaris, V. and Bernard-Salas, J. and Brandl, B. R. and Farrah, D. and Soifer, B. T. and Teplitz, H. I. and Ogle, P. M. and Devost, D. and Higdon, S. J. U. and Marshall, J. A. and Houck, J. R. (2007) PAH Emission from Ultraluminous Infrared Galaxies. Astrophysical Journal, 669 (2). pp. 810-820. ISSN 0004-637X.

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We explore the relationships between the polycyclic aromatic hydrocarbon (PAH) feature strengths, mid-infrared continuum luminosities, far-infrared spectral slopes, optical spectroscopic classifications, and silicate optical depths in a sample of 107 ULIRGs observed with the Infrared Spectrograph on the Spitzer Space Telescope. The detected 6.2 μm PAH equivalent widths (EWs) in the sample span more than 2 orders of magnitude (~0.006-0.8 μm), and ULIRGs with H II-like optical spectra or steep far-infrared spectral slopes (S_(25)/S_(60) < 0.2) typically have 6.2 μm PAH EWs that are half that of lower luminosity starbursts. A significant fraction (~40%-60%) of H II-like, LINER-like, and cold ULIRGs have very weak PAH EWs. Many of these ULIRGs also have large (τ_(9.7) > 2.3) silicate optical depths. The far-infrared spectral slope is strongly correlated with PAH EW, but not with silicate optical depth. In addition, the PAH EW decreases with increasing rest-frame 24 μm luminosity. We argue that this trend results primarily from dilution of the PAH EW by continuum emission from dust heated by a compact central source, probably an AGN. High-luminosity, high-redshift sources studied with Spitzer appear to have a much larger range in PAH EW than seen in local ULIRGs, which is consistent with extremely luminous starburst systems being absent at low redshift, but present at early epochs.

Item Type:Article
Related URLs:
URLURL TypeDescription
Desai, V.0000-0002-1340-0543
Armus, L.0000-0003-3498-2973
Spoon, H. W. W.0000-0002-8712-369X
Charmandaris, V.0000-0002-2688-1956
Bernard-Salas, J.0000-0002-8452-8675
Farrah, D.0000-0003-1748-2010
Teplitz, H. I.0000-0002-7064-5424
Ogle, P. M.0000-0002-3471-981X
Higdon, S. J. U.0000-0002-4021-7453
Marshall, J. A.0000-0001-7712-8465
Additional Information:© 2007 American Astronomical Society. Received 2007 January 7; accepted 2007 July 17. We would like to thank R. Chary, M. Lacy, J. Surace, and A. Sajina for insightful discussions. Support for this work was provided by NASA through an award issued by JPL/Caltech.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Subject Keywords:galaxies: active; galaxies: starburst; infrared: galaxies
Issue or Number:2
Record Number:CaltechAUTHORS:20100422-120905372
Persistent URL:
Official Citation:V. Desai et al 2007 ApJ 669 810 doi: 10.1086/522104
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:18049
Deposited By: Jason Perez
Deposited On:23 Apr 2010 15:43
Last Modified:04 Nov 2019 22:11

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