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 ($C = \log_{10}[S_{60μm}/S_{100μm}]$), total IR luminosity ($L_{TIR}$), radio surface brightness as well as 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 ultra-luminous 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 $C - L_{TIR}$ diagram. Among highly luminous galaxies, late type unbarred spirals are predominately warm, and early type unbarred and barred are systematically cooler. We highlight the significance of $C - L_{TIR}$ diagram in terms of local and high redshifts sub-millimeter galaxies.