The ISOPHOT 170 m Serendipity Survey^*

III. FIR statistics of optically identified galaxies

Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany e-mail: stickel@mpia.de

Received: 11 August 2006
Accepted: 7 November 2006

Abstract

Aims. To shed more light on the integrated FIR properties of galaxies, the ≈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 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 completeness limit of ≈2 Jy. The statistical analysis confirmed that the flux ratios peak at ≈1, corresponding to a dust color temperature of ≈20 K. FIR luminosities and dust masses cover a large range with peaks near and , respectively. HI-to-dust ratios range from ≈10 and ≈10⁴, rendering the notion of fiducial HI-to-dust ratio for conversion between gas and dust masses almost useless. The latest models of the cumulative number counts are in reasonable agreement with the deep as well as the shallow surveys from ISO up to fluxes of ≈50 Jy.