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Title:
Understanding the 8 μm versus Paα Relationship on Subarcsecond Scales in Luminous Infrared Galaxies
Authors:
Díaz-Santos, Tanio; Alonso-Herrero, Almudena; Colina, Luis; Packham, Christopher; Radomski, James T.; Telesco, Charles M.
Affiliation:
AA(Departamento de Astrofísica Molecular e Infrarroja, Instituto de Estructura de la Materia (IEM), CSIC, Serrano 121, E-28006 Madrid, Spain.), AB(Departamento de Astrofísica Molecular e Infrarroja, Instituto de Estructura de la Materia (IEM), CSIC, Serrano 121, E-28006 Madrid, Spain.), AC(Departamento de Astrofísica Molecular e Infrarroja, Instituto de Estructura de la Materia (IEM), CSIC, Serrano 121, E-28006 Madrid, Spain.), AD(Department of Astronomy, University of Florida, 211 Bryant Science Center, P.O. Box 112055, Gainesville, FL 32611-2055.), AE(Gemini Observatory, c/o AURA, Casilla 603, La Serena, Chile.), AF(Department of Astronomy, University of Florida, 211 Bryant Science Center, P.O. Box 112055, Gainesville, FL 32611-2055.)
Publication:
The Astrophysical Journal, Volume 685, Issue 1, pp. 211-224. (ApJ Homepage)
Publication Date:
09/2008
Origin:
UCP
ApJ Keywords:
Galaxies: Nuclei, Galaxies: Star Clusters, Galaxies: Starburst, Infrared: Galaxies
DOI:
10.1086/588276
Bibliographic Code:
2008ApJ...685..211D

Abstract

This work explores in detail the relation between the 8 μm and the Paα emissions for 122 H II regions identified in a sample of 10 low-z LIRGs with nearly constant metallicity [12+log(O/H)~8.8]. We use Gemini T-ReCS high spatial resolution (<~0.4"~120 pc for the average distance of 60 Mpc of our sample) mid-infrared imaging (at 8.7 or 10.3 μm), together with HST NICMOS continuum and Paα images. The LIRG H II regions extend the L8μm vs. LPaα relation found for H II knots in the high-metallicity SINGS galaxies by about 2 orders of magnitude to higher luminosities. Since the metallicity of the LIRG sample is nearly constant, we can rule out this effect as a cause for the scatter seen in the relationship. In turn, it is attributed to two effects: age and PAH features. The L8μm/LPaα ratio, which varies by a factor of 10 for the LIRG H II regions, is reproduced by a model with instantaneous star formation and ages ranging from ~4 to 7.5 Myr. The remaining dispersion around the model predictions for a given age is probably due to differential contributions of the PAH features (the 8.6 μm, in our case) to the 8 μm emission from galaxy to galaxy.

Based on observations obtained with T-ReCS instrument at the Gemini South Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: NSF (United States), PPARC (UK), NRC (Canada), CONICYT (Chile) ARC (Australia), CNPq (Brazil), and CONICET (Argentina).

Also based on observations with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-266555.

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