ISOPHOT 170 μm Serendipity Sky Survey: The First Galaxy Catalogue

Abstract

The ISOPHOT Serendipity Survey utilized the slew time between ISO’s pointedobserv ations with strip scanning measurements of the sky in the far-infrared at 170 μm. From the slew data with low (I_100μm ≤ 15 MJy/sr) cirrus background, 115 well-observedsources with a high signal-to-noise ratio in all four detector pixels having a galaxy association were extracted. The integral 170 μm fluxes measured from the Serendipity slews have been put on an absolute flux level by using a number of calibrator sources observedwith ISOPHOT’s photometric mapping mode. For all but a few galaxies, the 170 μm fluxes are determined for the first time, which represents a significant increase in the number of galaxies with measuredFIR fluxes beyondthe IRAS 100 μm limit. The vast majority of the galaxies are morphologically classifiedas spirals. The large fraction of sources with a high F_170μm/F_100μm flux ratio indicates that a very cold (T < 20 K) dust component is present in many galaxies. The typical mass of the coldest dust component is M_Dust = 10^7.5±0.5 M⊙, a factor 2 – 10 larger than that derived from IRAS fluxes alone. As a consequence, the gas-to-dust ratios are much closer to the canonical value of ≈ 160 for the Milky Way. By relaxing the selection criteria, it is expectedthat the Serendipity survey will eventually leadto a catalogue of 170 μm fluxes for ≈ 1000 galaxies.

Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA. Members of the Consortium on the ISOPHOT Serendipity Survey (CISS) are MPIA Heidelberg, ESA ISO SOC Villafranca, AIP Potsdam, IPAC Pasadena, Imperial College London.