The ISOPHOT 170 μm serendipity survey -: III.: FIR statistics of optically identified galaxies

Aims. To shed more light on the integrated FIR properties of galaxies, the approximate to 2000 compact sources in the ISOPHOT Serendipity Survey associated with identified galaxies are investigated statistically. They provide the only sample large enough to determine the FIR properties such as dust temperatures and masses, FIR luminosities, and HI-to-dust ratios not only for the group as a whole, but also divided into several subgroups of different Hubble types. Only with this catalog, the high flux end of the 170 mu m galaxy number counts can be established, which is crucial as a complement to the much deeper ISOPHOT studies at this wavelength in much smaller sky areas. Methods. The differential distributions of integrated FIR properties and the cumulative number counts are analysed. Results. The galaxy list of the ISOPHOT Serendipity Survey has a 170 mu m completeness limit of approximate to 2 Jy. The statistical analysis confirmed that the F-170 (mu m)/F-100 (mu m) flux ratios peak at approximate to 1, corresponding to a dust color temperature of approximate to 20 K. FIR luminosities and dust masses cover a large range with peaks near L1-1000 approximate to 10(10.5 +/- 1) L-circle dot and M-Dust approximate to 10(7.5 +/- 0.5) M-circle dot, respectively. HI-to-dust ratios range from approximate to 10 and approximate to 10(4), rendering the notion of fiducial HI-to-dust ratio for conversion between gas and dust masses almost useless. The latest models of the cumulative 170 mu m number counts are in reasonable agreement with the deep as well as the shallow surveys from ISO up to fluxes of approximate to 50 Jy.