Volume 591, July 2016
|Number of page(s)||16|
|Published online||01 June 2016|
Morphological classification of local luminous infrared galaxies
1 Department of Physics, University of Crete, 71003 Heraklion, Greece
2 IAASARS, National Observatory of Athens, 15236 Penteli, Greece
3 Núcleo de Astronomía de la Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago, Chile
4 Spitzer Science Center, Calfornia Institute of Technology, MS 220-6, Pasadena, CA 91125, USA
5 CSIRO Astronomy and Space Science, ATNF, PO Box 76, Epping 1710, Australia
6 Infrared Processing and Analysis Center, California Institute of Technology, MS 100-22, Pasadena, CA 91125, USA
7 CEA Saclay, DSM/Irfu/Service d’Astrophysique, Orme des Merisiers, 91191 Gif-sur-Yvette Cedex, France
8 Department of Physics, Virginia Tech, Blacksburg, VA 24061, USA
9 Department of Astronomy, University of Virginia, Charlottesville, VA 22904, USA
10 National Radio Astronomy Observatory, Charlottesville, VA 22903, USA
Received: 8 January 2016
Accepted: 22 February 2016
We present analysis of the morphological classification of 89 luminous infrared galaxies (LIRGs) from the Great Observatories All-sky LIRG Survey (GOALS) sample, using non-parametric coefficients and compare their morphology as a function of wavelength. We rely on images that were obtained in the optical (B- and I-band) as well as in the infrared (H-band and 5.8 μm). Our classification is based on the calculation of Gini and the second order of light (M20) non-parametric coefficients, which we explore as a function of stellar mass (M⋆), infrared luminosity (LIR), and star formation rate (SFR). We investigate the relation between M20, the specific SFR (sSFR) and the dust temperature (Tdust) in our galaxy sample. We find that M20 is a better morphological tracer than Gini, as it allows us to distinguish systems that were formed by double systems from isolated and post-merger LIRGs. The effectiveness of M20 as a morphological tracer increases with increasing wavelength, from the B to H band. In fact, the multi-wavelength analysis allows us to identify a region in the Gini-M20 parameter space where ongoing mergers reside, regardless of the band used to calculate the coefficients. In particular, when measured in the H band, a region that can be used to identify ongoing mergers, with minimal contamination from LIRGs in other stages. We also find that, while the sSFR is positively correlated with M20 when measured in the mid-infrared, i.e. star-bursting galaxies show more compact emission, it is anti-correlated with the B-band-based M20. We interpret this as the spatial decoupling between obscured and unobscured star formation, whereby the ultraviolet/optical size of an LIRG experience an intense dust-enshrouded central starburst that is larger that in the mid-infrared since the contrast between the nuclear to the extended disk emission is smaller in the mid-infrared. This has important implications for high redshift surveys of dusty sources, where sizes of galaxies are routinely measured in the rest-frame ultraviolet.
Key words: Galaxy: structure / infrared: galaxies / galaxies: evolution / galaxies: general / galaxies: starburst
© ESO, 2016
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