Astron. Astrophys. 359, 865-875 (2000)

The ISOPHOT 170µm serendipity survey

I. Compact sources with galaxy associations ^*

M. Stickel ¹, D. Lemke ¹, U. Klaas ¹, C.A. Beichman ², M. Rowan-Robinson ³, A. Efstathiou ³, S. Bogun ⁴, M. F. Kessler ⁵ and G. Richter <sup>6

1</sup> Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
² Infrared Processing and Analysis Center, JPL, California Institute of Technology, MS 100/22, Pasadena, CA 91125, USA
³ Imperial College of Science, Technology and Medicine, The Blackett Laboratory, Prince Consort Road, London SW7 2BZ, UK
⁴ Data Management and Operations Division, ESO, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
⁵ ISO Data Centre, Astrophysics Divison, Space Science Department of ESA, Villafranca, P.O. Box 50727, 28080 Madrid, Spain
⁶ Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany

Received 16 February 2000 / Accepted 9 May 2000

Abstract

The first set of compact sources observed in the ISOPHOT 170 µm Serendipity Survey is presented. From the slew data with low ( 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 2 100 Jy. Formulae for the integrated FIR fluxes and the total infrared fluxes incorporating the new 170 µm fluxes are provided. The large fraction of sources with a high flux ratio indicates that a cold ( 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 flux ratio, increases the dust mass by a significant factor. The typical mass of the coldest dust component is = , 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.

Key words: methods: data analysis catalogs surveys galaxies: ISM infrared: 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

Send offprint requests to: M. Stickel

Correspondence to: stickel@mpia-hd.mpg.de

© European Southern Observatory (ESO) 2000

Online publication: July 13, 2000

helpdesk.link@springer.de