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Mid-infrared Properties of Luminous Infrared Galaxies. II. Probing the Dust and Gas Physics of the GOALS Sample

Stierwalt, S. and Armus, L. and Charmandaris, V. and Díaz-Santos, T. and Marshall, J. and Evans, A. S. and Haan, S. and Howell, J. and Iwasawa, K. and Kim, D. C. and Murphy, E. J. and Rich, J. A. and Spoon, H. W. W. and Inami, H. and Petric, A. O. and U, V. (2014) Mid-infrared Properties of Luminous Infrared Galaxies. II. Probing the Dust and Gas Physics of the GOALS Sample. Astrophysical Journal, 790 (2). Art. No. 124. ISSN 0004-637X. https://resolver.caltech.edu/CaltechAUTHORS:20140815-092818574

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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 the results of a multi-component, spectral decomposition analysis of the low-resolution mid-infrared (MIR) Spitzer Infrared Spectrograph spectra from 5–38  μm of 244 LIRG nuclei. The detailed fits and high-quality spectra allow for characterization of the individual polycyclic aromatic hydrocarbon (PAH) features, warm molecular hydrogen emission, and optical depths for both silicate dust grains and water ices. We find that starbursting LIRGs, which make up the majority of the GOALS sample, are very consistent in their MIR properties (i.e., τ_(9.7 μm), τ_(ice), neon line ratios, and PAH feature ratios). However, as their EQW6.2 μm decreases, usually an indicator of an increasingly dominant active galactic nucleus (AGN), LIRGs cover a larger spread in these MIR parameters. The contribution from PAH emission to the total IR luminosity (L(PAH)/L(IR)) in LIRGs varies from 2%–29% and LIRGs prior to their first encounter show significantly higher L(PAH)/L(IR) ratios on average. We observe a correlation between the strength of the starburst (represented by IR8 = L_(IR)/L_(8 μm)) and the PAH fraction at 8 μm but no obvious link between IR8 and the 7.7 to 11.3 PAH ratio, suggesting that the fractional photodissociation region (PDR) emission, and not the overall grain properties, is associated with the rise in IR8 for galaxies off the starburst main sequence. We detect crystalline silicate features in ~6% of the sample but only in the most obscure sources (s_(9.7 μm) < −1.24). Ice absorption features are observed in ~11% (56%) of GOALS LIRGs (ULIRGs) in sources with a range of silicate depths. Most GOALS LIRGs have L(H2)/L(PAH) ratios elevated above those observed for normal star-forming galaxies and exhibit a trend for increasing L(H2)/L(PAH) ratio with increasing L(H2). While star formation appears to be the dominant process responsible for exciting the H2 in most of the GOALS galaxies, a subset of LIRGs (~10%) shows excess H2 emission that is inconsistent with PDR models and may be excited by shocks or AGN-induced outflows.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1088/0004-637X/790/2/124DOIArticle
http://iopscience.iop.org/0004-637X/790/2/124/articlePublisherArticle
http://arxiv.org/abs/1406.3891arXivDiscussion Paper
ORCID:
AuthorORCID
Stierwalt, S.0000-0002-2596-8531
Armus, L.0000-0003-3498-2973
Charmandaris, V.0000-0002-2688-1956
Díaz-Santos, T.0000-0003-0699-6083
Evans, A. S.0000-0003-2638-1334
Iwasawa, K.0000-0002-4923-3281
Murphy, E. J.0000-0001-7089-7325
Rich, J. A.0000-0002-5807-5078
Spoon, H. W. W.0000-0002-8712-369X
Inami, H.0000-0003-4268-0393
Petric, A. O.0000-0003-4030-3455
U, V.0000-0002-1912-0024
Additional Information:© 2014 The American Astronomical Society. Received 2014 March 1; accepted 2014 June 12; published 2014 July 14. 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. This work was supported in part by National Science Foundation grant No. PHYS-1066293 and the hospitality of the Aspen Center for Physics. V.C. acknowledges partial support from the EU FP7 grant PIRSES-GA-2012-316788. The authors thank M. Cluver for many helpful discussions and the anonymous referee for help in improving the paper.
Group:Infrared Processing and Analysis Center (IPAC)
Funders:
Funding AgencyGrant Number
NSFPHYS-1066293
Marie Curie FellowshipPIRSES-GA-2012-316788
NASA1407
Subject Keywords:galaxies: interactions; galaxies: nuclei; galaxies: starburst; galaxies: star formation
Issue or Number:2
Record Number:CaltechAUTHORS:20140815-092818574
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20140815-092818574
Official Citation:Mid-infrared Properties of Luminous Infrared Galaxies. II. Probing the Dust and Gas Physics of the GOALS Sample S. Stierwalt et al. 2014 ApJ 790 124
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48600
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:15 Aug 2014 17:12
Last Modified:09 Mar 2020 13:19

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