Petric, A. O. and Armus, L. and Howell, J. and Chan, B. and Mazzarella, J. M. and Evans, A. S. and Surace, J. A. and Sanders, D. and Appleton, P. and Charmandaris, V. and Díaz-Santos, T. and Frayer, D. and Haan, S. and Inami, H. and Iwasawa, K. and Kim, D. and Madore, B. and Marshall, J. and Spoon, H. and Stierwalt, S. and Sturm, E. and U, V. and Vavilkin, T. and Veilleux, S. (2011) Mid-Infrared Spectral Diagnostics of Luminous Infrared Galaxies. Astrophysical Journal, 730 (1). Art. No. 28. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20110419-094815329
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We present a statistical analysis of the mid-infrared (MIR) spectra of 248 luminous infrared (IR) galaxies (LIRGs) which comprise the Great Observatories All-sky LIRG Survey (GOALS) observed with the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. The GOALS sample enables a direct measurement of the relative contributions of star formation and active galactic nuclei (AGNs) to the total IR emission from a large sample of local LIRGs. The AGN contribution to the MIR emission (f_(AGN)) is estimated by employing several diagnostics based on the properties of the [Ne_V], [O_(IV)], and [Ne_(II)] fine-structure gas emission lines, the 6.2 μm polycyclic aromatic hydrocarbon (PAH), and the shape of the MIR continuum. We find that 18% of all LIRGs contain an AGN and that in 10% of all sources the AGN contributes more than 50% of the total IR luminosity. Summing up the total IR luminosity contributed by AGNs in all our sources suggests that AGNs supply ~12% of the total energy emitted by LIRGs. The average spectrum of sources with an AGN looks similar to the average spectrum of sources without an AGN, but it has lower PAH emission and a flatter MIR continuum. AGN-dominated LIRGs have higher IR luminosities, warmer MIR colors, and are found in interacting systems more often than pure starburst LIRGs. However, we find no linear correlations between these properties and f_(AGN). We used the IRAC colors of LIRGs to confirm that finding AGNs on the basis of their MIR colors may miss ~40% of AGN-dominated (U)LIRGs.
|Additional Information:||© 2011 American Astronomical Society. Received 2010 September 8; accepted 2010 December 8; published 2011 March 1. We thank the anonymous referee for his comments which have significantly improved our paper. V.C. acknowledges partial support from the EU grants ToK 39965 and FP7- REGPOT 206469. A.P. thanks N. Flagey for multiple readings of the document and comments which helped improve the clarity of this text. A.P. also thanks V. Desai for help with the data analysis, and C. Bridge for discussions and help with the merger classification of the LIRGs in this paper. This work is based primarily on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. We have made use of the NASA/IPAC Extra-galactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Support for this research was provided by NASA through an award issued by JPL/Caltech.|
|Subject Keywords:||galaxies: evolution – galaxies: interactions|
|Classification Code:||PACS: 98.54.Ep, 98.54.Cm, 98.62.Qz, 98.62.Bj, 95.85.Hp|
|Official Citation:||A. O. Petric et al. 2011 ApJ 730 28 doi: 10.1088/0004-637X/730/1/28|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Benjamin Perez|
|Deposited On:||19 Apr 2011 17:17|
|Last Modified:||26 Dec 2012 13:10|
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