Probing Cool and Warm Infrared Galaxies Using Photometric and Structural Measures

Abstract

We have analyzed a sample of nearby cool and warm infrared (IR) galaxies using photometric and structural parameters. The set of measures include far-infrared color [C = log(S_(60 μm)/S_(100 μm))], total IR luminosity (L_TIR), radio surface brightness, and radio, near-infrared, and optical sizes. In a given luminosity range cool and warm galaxies are considered as those sources that are found approximately 1 σ below and above the mean color in the far-infrared C-L_TIR diagram. We find that galaxy radio surface brightness is well correlated with color whereas size is less well correlated with color. Our analysis indicates that IR galaxies that are dominated by cool dust are large, massive spirals that are not strongly interacting or merging and presumably the ones with the least active star formation. Dust in these cool objects is less centrally concentrated than in the more typical luminous and ultraluminous IR galaxies that are dominated by warm dust. Our study also shows that low-luminosity early-type unbarred and transitional spirals are responsible for the large scatter in the C-LTIR diagram. Among highly luminous galaxies, late-type unbarred spirals are predominately warm, and early-type unbarred and barred spirals are systematically cooler. We highlight the significance of the C-L_TIR diagram in terms of local and high-redshift submillimeter galaxies.

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