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Mid-infrared Properties of Nearby Luminous Infrared Galaxies. I. Spitzer Infrared Spectrograph Spectra for the GOALS Sample

Stierwalt, S. and Armus, L. and Surace, J. A. and Inami, H. and Petric, A. O. and Díaz-Santos, T. and Haan, S. and Howell, J. and Marshall, J. and Mazzarella, J. M. and Bridge, C. R. and Melbourne, J. E. and Chan, B. and Lord, S. and Xu, K. and Appleton, P. and Schulz, B. (2013) Mid-infrared Properties of Nearby Luminous Infrared Galaxies. I. Spitzer Infrared Spectrograph Spectra for the GOALS Sample. Astrophysical Journal Supplement Series, 206 (1). Art. No. 1. ISSN 0067-0049. http://resolver.caltech.edu/CaltechAUTHORS:20130408-102147094

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Abstract

The Great Observatories All-Sky LIRG Survey (GOALS) is a comprehensive, multiwavelength study of luminous infrared galaxies (LIRGs) in the local universe. Here we present low resolution Spitzer Infrared Spectrograph spectra covering 5-38 μm and provide a basic analysis of the mid-IR spectral properties observed for nearby LIRGs. In a companion paper, we discuss detailed fits to the spectra and compare the LIRGs to other classes of galaxies. The GOALS sample of 244 nuclei in 180 luminous (10^(11) ≤ L_(IR)/L_☉ < 10^(12)) and 22 ultraluminous (L_(IR)/L_☉ ≥ 10^(12)) IR galaxies represents a complete subset of the IRAS Revised Bright Galaxy Sample and covers a range of merger stages, morphologies, and spectral types. The majority (>60%) of the GOALS LIRGs have high 6.2 μm polycyclic aromatic hydrocarbon (PAH) equivalent widths (EQW_(6.2 μm) > 0.4 μm) and low levels of silicate absorption (s 9.7 μm > –1.0). There is a general trend among the U/LIRGs for both silicate depth and mid-infrared (MIR) slope to increase with increasing L_(IR). U/LIRGs in the late to final stages of a merger also have, on average, steeper MIR slopes and higher levels of dust obscuration. Together, these trends suggest that as gas and dust is funneled toward the center of a coalescing merger, the nuclei become more compact and more obscured. As a result, the dust temperature increases also leading to a steeper MIR slope. The sources that depart from these correlations have very low PAH equivalent width (EQW_(6.2 μm) < 0.1 μm) consistent with their emission being dominated by an active galactic nucleus (AGN) in the MIR. These extremely low PAH EQW sources separate into two distinct types: relatively unobscured sources with a very hot dust component (and thus very shallow MIR slopes) and heavily dust obscured nuclei with a steep temperature gradient. The most heavily dust obscured sources are also the most compact in their MIR emission, suggesting that the obscuring (cool) dust is associated with the outer regions of the starburst and not simply a measure of the dust along the line of sight through a large, dusty disk. A marked decline is seen for the fraction of high EQW (star formation dominated) sources as the merger progresses. The decline is accompanied by an increase in the fraction of composite sources while the fraction of sources where an AGN dominates the MIR emission remains low. When compared to the MIR spectra of submillimeter galaxies (SMGs) at z ~ 2, both the average GOALS LIRG and ULIRG spectra are more absorbed at 9.7 μm and the average GOALS LIRG has more PAH emission. However, when the AGN contributions to both the local GOALS LIRGs and the high-z SMGs are removed, the average local starbursting LIRG closely resembles the starburst-dominated SMGs.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1088/0067-0049/206/1/1DOIArticle
http://iopscience.iop.org/0067-0049/206/1/1/PublisherArticle
http://arxiv.org/abs/1302.4477arXivDiscussion Paper
ORCID:
AuthorORCID
Surace, J. A.0000-0001-7291-0087
Díaz-Santos, T.0000-0003-0699-6083
Mazzarella, J. M.0000-0002-8204-8619
Appleton, P.0000-0002-7607-8766
Alternate Title:Mid-Infrared Properties of Nearby Luminous Infrared Galaxies I: Spitzer IRS Spectra for the GOALS Sample
Additional Information:© 2013 American Astronomical Society. Received 2012 July 13; accepted 2013 February 7; published 2013 April 18. The Spitzer Space Telescope is operated by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407. 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 made use of the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics Space Administration. We thank M. Cluver formany helpful discussions and K. Menéndez-Delmestre for sharing her average SMG spectra.
Group:Infrared Processing and Analysis Center (IPAC)
Funders:
Funding AgencyGrant Number
NASA1407
NASA/JPL/CaltechUNSPECIFIED
Record Number:CaltechAUTHORS:20130408-102147094
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20130408-102147094
Official Citation:S. Stierwalt et al 2013 ApJS 206 1
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37804
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:08 Apr 2013 18:07
Last Modified:25 Oct 2017 19:38

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