THE SPATIAL EXTENT OF (U)LIRGs IN THE MID-INFRARED. I. THE CONTINUUM EMISSION
- Department of Physics, University of Crete, GR-71003, Heraklion (Greece)
- Spitzer Science Center, Caltech, MS 220-6, Pasadena, CA 91125 (United States)
- Infrared Processing and Analysis Center, MS 100-22, California Institute of Technology, Pasadena, CA 91125 (United States)
- Department of Physics and Astronomy, University of New York at Stony Brook, NY 11794-3800 (United States)
- Department of Physics, University of Oregon, Eugene, OR 97403 (United States)
- NASA Herschel Science Center, IPAC, MS 100-22, Caltech, Pasadena, CA 91125 (United States)
- Department of Astronomy, 530 McCormick Road, University of Virginia, Charlottesville, VA 22904 (United States)
We present an analysis of the extended mid-infrared (MIR) emission of the Great Observatories All-Sky LIRG Survey sample based on 5-15 {mu}m low-resolution spectra obtained with the Infrared Spectrograph on Spitzer. We calculate the fraction of extended emission (FEE) as a function of wavelength for the galaxies in the sample, FEE{sub {lambda}}, defined as the fraction of the emission which originates outside of the unresolved component of a source at a given distance. We find that the FEE{sub {lambda}} varies from one galaxy to another, but we can identify three general types of FEE{sub {lambda}:} one where FEE{sub {lambda}} is constant, one where features due to emission lines and polycyclic aromatic hydrocarbons appear more extended than the continuum, and a third which is characteristic of sources with deep silicate absorption at 9.7 {mu}m. More than 30% of the galaxies have a median FEE{sub {lambda}} larger than 0.5, implying that at least half of their MIR emission is extended. Luminous Infrared Galaxies (LIRGs) display a wide range of FEE in their warm dust continuum (0 {approx}< FEE{sub 13.2{sub {mu}m}} {approx}< 0.85). The large values of FEE{sub 13.2{sub {mu}m}} that we find in many LIRGs suggest that the extended component of their MIR continuum emission originates in scales up to 10 kpc and may contribute as much as the nuclear region to their total MIR luminosity. The mean size of the LIRG cores at 13.2 {mu}m is 2.6 kpc. However, once the IR luminosity of the systems reaches the threshold of L{sub IR} {approx} 10{sup 11.8} L{sub sun}, slightly below the regime of Ultra-luminous Infrared Galaxies (ULIRGs), all sources become clearly more compact, with FEE{sub 13.2{sub {mu}m}} {approx}< 0.2, and their cores are unresolved. Our estimated upper limit for the core size of ULIRGs is less than 1.5 kpc. Furthermore, our analysis indicates that the compactness of systems with L{sub IR} {approx}> 10{sup 11.25} L{sub sun} strongly increases in those classified as mergers in their final stage of interaction. The FEE{sub 13.2{sub {mu}m}} is also related to the contribution of an active galactic nucleus (AGN) to the MIR emission. Galaxies which are more AGN dominated are less extended, independently of their L{sub IR}. We finally find that the extent of the MIR continuum emission is correlated with the far-IR IRAS log(f{sub 60{sub {mu}m}}/f{sub 100{sub {mu}m}}) color. This enables us to place a lower limit to the area in a galaxy from where the cold dust emission may originate, a prediction which can be tested soon with the Herschel Space Telescope.
- OSTI ID:
- 21471290
- Journal Information:
- Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 723; ISSN ASJOAB; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ABSORPTION
AROMATICS
COLOR
DUSTS
EMISSION
EVOLUTION
GALACTIC EVOLUTION
GALAXIES
HYDROCARBONS
LUMINOSITY
OPTICAL PROPERTIES
ORGANIC COMPOUNDS
ORGANOLEPTIC PROPERTIES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
POLYCYCLIC AROMATIC HYDROCARBONS
SILICATES
SILICON COMPOUNDS
SORPTION
TELESCOPES