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Mid-infrared Atomic Fine-structure Emission-line Spectra of Luminous Infrared Galaxies: Spitzer/IRS Spectra of the GOALS Sample

Inami, H. and Armus, L. and Charmandaris, V. and Groves, B. and Kewley, L. and Petric, A. and Stierwalt, S. and Díaz-Santos, T. and Surace, J. and Rich, J. and Haan, S. and Howell, J. and Evans, A. S. and Mazzarella, J. and Marshall, J. and Appleton, P. and Lord, S. and Spoon, H. and Frayer, D. and Matsuhara, H. and Veilleux, S. (2013) Mid-infrared Atomic Fine-structure Emission-line Spectra of Luminous Infrared Galaxies: Spitzer/IRS Spectra of the GOALS Sample. Astrophysical Journal, 777 (2). Art. No. 156. ISSN 0004-637X.

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We present the data and our analysis of mid-infrared atomic fine-structure emission lines detected in Spitzer/Infrared Spectrograph high-resolution spectra of 202 local Luminous Infrared Galaxies (LIRGs) observed as part of the Great Observatories All-sky LIRG Survey (GOALS). We readily detect emission lines of [S IV], [Ne II], [Ne V], [Ne III], [S III]18.7 μm, [O IV], [Fe II], [S III]_(33.5 μm), and [Si II]. More than 75% of these galaxies are classified as starburst-dominated sources in the mid-infrared, based on the [Ne V]/[Ne II] line flux ratios and equivalent width of the 6.2 μm polycyclic aromatic hydrocarbon feature. We compare ratios of the emission-line fluxes to those predicted from stellar photo-ionization and shock-ionization models to constrain the physical and chemical properties of the gas in the starburst LIRG nuclei. Comparing the [S IV]/[Ne II] and [Ne III]/[Ne II] line ratios to the Starburst99-Mappings III models with an instantaneous burst history, the emission-line ratios suggest that the nuclear starbursts in our LIRGs have ages of 1-4.5 Myr, metallicities of 1-2 Z_☉, and ionization parameters of 2-8 × 10^7 cm s^(–1). Based on the [S III]_(33.5 μm)/[S III]_(18.7 μm) ratios, the electron density in LIRG nuclei is typically one to a few hundred cm^(–3), with a median electron density of ~300 cm^(–3), for those sources above the low density limit for these lines. We also find that strong shocks are likely present in 10 starburst-dominated sources of our sample. A significant fraction of the GOALS sources (80) have resolved neon emission-line profiles (FWHM ≥600 km s^(–1)) and five show clear differences in the velocities of the [Ne III] or [Ne V] emission lines, relative to [Ne II], of more than 200 km s^(–1). Furthermore, six starburst and five active galactic nucleus dominated LIRGs show a clear trend of increasing line width with ionization potential, suggesting the possibility of a compact energy source and stratified interstellar medium in their nuclei. We confirm a strong correlation between the sum of the [Ne II]_(12.8 μm) and [Ne III]_(15.5 μm) emission, as well as [S III]_(33.5 μm), with both the infrared luminosity and the 24 μm warm dust emission measured from the spectra, consistent with all three lines tracing ongoing star formation. Finally, we find no correlation between the hardness of the radiation field or the emission-line width and the ratio of the total infrared to 8 μm emission (IR8), a measure of the strength of the starburst and the distance of the LIRGs from the star-forming main sequence. This may be a function of the fact that the infrared luminosity and the mid-infrared fine-structure lines are sensitive to different timescales over the starburst, or that IR8 is more sensitive to the geometry of the region emitting the warm dust than the radiation field producing the H II region emission.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Inami, H.0000-0003-4268-0393
Armus, L.0000-0003-3498-2973
Charmandaris, V.0000-0002-2688-1956
Groves, B.0000-0002-9768-0246
Kewley, L.0000-0001-8152-3943
Petric, A.0000-0003-4030-3455
Stierwalt, S.0000-0002-2596-8531
Díaz-Santos, T.0000-0003-0699-6083
Surace, J.0000-0001-7291-0087
Evans, A. S.0000-0003-2638-1334
Mazzarella, J.0000-0002-8204-8619
Appleton, P.0000-0002-7607-8766
Spoon, H.0000-0002-8712-369X
Frayer, D.0000-0003-1924-1122
Veilleux, S.0000-0002-3158-6820
Additional Information:© 2013 American Astronomical Society. Received 2013 May 8; accepted 2013 September 16; published 2013 October 24. The authors appreciate the referee’s useful suggestions which improved the manuscript. The authors are grateful to E. Levesque for providing the stellar photo-ionization models. H.I. thanks Grant-in-Aid for Japan Society for the Promotion of Science (JSPS) Fellows (21-969) and JSPS Excellent Young Researchers Overseas Visit Program for supporting this work. L.A. acknowledges the hospitality of the Aspen Center for Physics, which is supported by the National Science Foundation grant No. PHY-1066293. V.C. would like to acknowledge partial support from the EU FP7 Grant PIRSES-GA-2012-316788. 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) and the Infrared Science Archive (IRSA) which are operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Facility: Spitzer
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Japan Society for the Promotion of Science (JSPS)21-969
Marie Curie FellowshipPIRSES-GA-2012-316788
Subject Keywords:galaxies: ISM; galaxies: starburst; infrared: galaxies
Issue or Number:2
Record Number:CaltechAUTHORS:20131202-142002525
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Official Citation:Mid-infrared Atomic Fine-structure Emission-line Spectra of Luminous Infrared Galaxies: Spitzer/IRS Spectra of the GOALS Sample H. Inami et al. 2013 ApJ 777 156
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42777
Deposited By: Ruth Sustaita
Deposited On:02 Dec 2013 22:47
Last Modified:09 Mar 2020 13:19

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