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We have studied the properties of more than 1600 low-redshift galaxies byutilizing high-quality infrared flux measurements of the AKARI All-Sky Surveyand physical quantities based on optical and 21-cm observations. Our goal is tounderstand the physics determining the infrared spectral energy distribution(SED). The ratio of the total infrared luminosity L_TIR, to the star-formationrate (SFR) is tightly correlated by a power-law to specific SFR (SSFR), andL_TIR is a good SFR indicator only for galaxies with the largest SSFR. Wediscovered a tight linear correlation for normal galaxies between the radiationfield strength of dust heating, estimated by infrared SED fits (U_h), and thatof galactic-scale infrared emission (U_TIR ~ L_TIR/R^2), where R is the opticalsize of a galaxy. The dispersion of U_h along this relation is 0.3 dex,corresponding to 13% dispersion in the dust temperature. This scaling and theU_h/U_TIR ratio can be explained physically by a thin layer of heating sourcesembedded in a thicker, optically-thick dust screen. The data also indicate thatthe heated fraction of the total dust mass is anti-correlated to the dustcolumn density, supporting this interpretation. In the large U_TIR limit, thedata of circumnuclear starbursts indicate the existence of an upper limit onU_h, corresponding to the maximum SFR per gas mass of ~ 10 Gyr^{-1}. We findthat the number of galaxies sharply drops when they become optically thinagainst dust-heating radiation, suggesting that a feedback process to galaxyformation (likely by the photoelectric heating) is working when dust-heatingradiation is not self-shielded on a galactic scale. Implications are discussedfor the M_HI-size relation, the Kennicutt-Schmidt relation, and galaxyformation in the cosmological context.

Infrared Spectral Energy Distribution of Galaxies in the AKARI All Sky Survey: Correlations with Galaxy Properties, and Their Physical Origin