The ISOPHOT 170 μ m serendipity survey. I. Compact sources with galaxy associations
Abstract
The first set of compact sources observed in the ISOPHOT 170 μm Serendipity Survey is presented. From the slew data with low (I100 μm <= 15 MJy/sr) cirrus background, 115 well-observed sources with a high signal-to-noise ratio in all detector pixels having a galaxy association were extracted. Of the galaxies with known optical morphologies, the vast majority are classified as spirals, barred spirals, or irregulars. The 170 μm fluxes measured from the Serendipity slews have been put on an absolute flux level by using calibration sources observed additionally with the photometric mapping mode of ISOPHOT. 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 measured Far-Infrared (FIR) fluxes beyond the IRAS 100 μm limit. The 170 μm fluxes cover the range 2 <~ F170 μm la 100 Jy. Formulae for the integrated FIR fluxes F40-220μm and the total infrared fluxes F1-1000μm incorporating the new 170 μm fluxes are provided. The large fraction of sources with a high F170 μm / F100 μm flux ratio indicates that a cold (TDust la 20 K) dust component is present in many galaxies. The detection of such a cold dust component is crucial for the determination of the total dust mass in galaxies, and, in cases with a large F170 μm / F100 μm flux ratio, increases the dust mass by a significant factor. The typical mass of the coldest dust component is MDust = 107.5 +/- 0.5 Msun , a factor 2-10 larger than that derived from IRAS fluxes alone. As a consequence, the majority of the derived gas-to-dust ratios are much closer to the canonical value of ~ 160 for the Milky Way. By relaxing the selection criteria, it is expected that the Serendipity Survey will eventually lead to a catalog 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.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- July 2000
- Bibcode:
- 2000A&A...359..865S
- Keywords:
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- METHODS: DATA ANALYSIS;
- CATALOGS;
- SURVEYS;
- GALAXIES: ISM;
- INFRARED: GALAXIES