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The Spatial Extent of (U)LIRGS in the Mid-infrared. II. Feature Emission

Díaz-Santos, T. and Charmandaris, V. and Armus, L. and Stierwalt, S. and Haan, S. and Mazzarella, J. M. and Howell, J. H. and Veilleux, S. and Murphy, E. J. and Petric, A. O. and Appleton, P. and Evans, A. S. and Sanders, D. B. and Surace, J. A. (2011) The Spatial Extent of (U)LIRGS in the Mid-infrared. II. Feature Emission. Astrophysical Journal, 741 (1). Art. No. 32. ISSN 0004-637X.

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We present results from the second part of our analysis of the extended mid-infrared (MIR) emission of the GOALS sample based on 5–14μm low-resolution spectra obtained with the Infrared Spectrograph on Spitzer. We calculate the fraction of extended emission (FEE) as a function of wavelength for all galaxies in the sample, FEE_λ, defined as the fraction of the emission that originates outside of the unresolved central component of a source, and spatially separate the MIR spectrum of a galaxy into its nuclear and extended components. We find that the [Ne ii]12.81μm emission line is as compact as the hot dust MIR continuum, while the polycyclic aromatic hydrocarbon (PAH) emission is more extended. In addition, the 6.2 and 7.7μm PAH emission is more compact than that of the 11.3μm PAH, which is consistent with the formers being enhanced in a more ionized medium. The presence of an active galactic nucleus (AGN) or a powerful nuclear starburst increases the compactness and the luminosity surface density of the hot dustMIR continuum, but has a negligible effect on the spatial extent of the PAH emission on kpc-scales. Furthermore, it appears that both processes, AGN and/or nuclear starburst, are indistinguishable in terms of how they modify the integrated PAH-to-continuum ratio of the FEE in (ultra)luminous infrared galaxies ((U)LIRGs). Globally, the 5–14μm spectra of the extended emission component are homogeneous for all galaxies in the GOALS sample. This suggests that, independently of the spatial distribution of the various MIR features, the physical properties of star formation occurring at distances farther than 1.5 kpc from the nuclei of (U)LIRGs are very similar, resembling local star-forming galaxies with L_(IR) < 10^(11) L_☉, as well as star-formation-dominated ULIRGs at z ~ 2. In contrast, the MIR spectra of the nuclear component of local ULIRGs and LIRGs are very diverse. These results imply that the observed variety of the integrated MIR properties of local (U)LIRGs arise, on average, only from the processes that are taking place in their cores.

Item Type:Article
Related URLs:
URLURL TypeDescription
Díaz-Santos, T.0000-0003-0699-6083
Mazzarella, J. M.0000-0002-8204-8619
Veilleux, S.0000-0002-3158-6820
Murphy, E. J.0000-0001-7089-7325
Appleton, P.0000-0002-7607-8766
Surace, J. A.0000-0001-7291-0087
Additional Information:© 2011 The American Astronomical Society. Received 2011 April 19; accepted 2011 July 27; published 2011 October 12. We thank the referee for her/his useful comments which helped to improved the paper. T.D.-S. thanks D. Elbaz, E. Le Floc’h, V. Lebouteiller, E. Daddi, and G. Magdis for stimulating discussions, as well as all colleagues at CEA/Saclay (France), where part of this work was done, for their hospitality. T.D.-S. and V.C. acknowledge partial support from the EU ToK grant 39965 and FP7-REGPOT 206469. 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, and of NASA’s Astrophysics Data System (ADS) abstract service.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
European Research Council (ERC)39965
European Research Council (ERC)206469
Subject Keywords:galaxies: active; galaxies: evolution; galaxies: interactions; galaxies: starburst; infrared: galaxies
Record Number:CaltechAUTHORS:20111206-104046218
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Official Citation:The Spatial Extent of (U)LIRGS in the Mid-infrared. II. Feature Emission T. Díaz-Santos et al. 2011 ApJ 741 32
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:28316
Deposited By: Ruth Sustaita
Deposited On:06 Dec 2011 19:16
Last Modified:25 Oct 2017 19:41

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