Common Correlations between 60, 100, and 140$\, {\mu \mathrm {m}}$ Intensities in the Galactic Plane and Magellanic Clouds

We investigate the far-infrared SED of the Galaxy and the Magellanic Cloudsby using the COBE (COsmic Background Explorer) / DIRBE (Diffuse InfraRedBackground Experiment) ZSMA (Zodi - Subtracted Mission Average) maps atwavelengths of 60 um, 100 um and 140 um. We analyze three regions: the Galacticplane region with the Galactic latitude |b|<5 degree, the Large MagellanicCloud (LMC) region, and the Small Magellanic Cloud (SMC) region. Because thedust optical depth is much smaller in the far-infrared than in the visible, wemay observe cumulative far-infrared radiation from regions with variousinterstellar radiation field (IRSF) in a line of sight. As consequence ofconsidering such an effect, we find a common far-infrared color correlationbetween the 140 - 100 um and 60 - 100 um intensity ratios in all the threegalaxies. Although this color correlation cannot be explained by any existingmodel, it fits very well the far-infrared color of nearby star forminggalaxies.Comment: Accepted for publication in The Publications of the Astronomical Society of Japan. 11 pages, 9 figure