NGC 5195 - a look into the hot dusty ISM of an interacting SB0 galaxy with ISOCAM

Abstract. We present broad-bandimages and a CVF spectrumof NGC5195, the companion of M51. NGC5195 appears as avery strong point source while its spectrum is dominatedby theso-calledPAH featuresat6.2,7.7,8.6,and11.3  m.Nohotcon-tinuum is detected longward of 14  m, and infrared ionic linesare absent from the spectrum. We examine in turn possibilitiesfor the generation of this infrared emission: (1) photospheresor circumstellar envelopes, (2) an embedded current starburst,(3) a LINER, and (4) the evolved starburst population. We findthat only 3 and 4 are compatible with the data and tend to pre-fer 4 since ionic lines expected in LINERs are absent. We alsoshow that, to produce the detected flux, the dust has to take asubstantial fraction of its heating energy from optical photons,eventhough PAH features dominate the emission.Key words: galaxies: individual: NGC5195 – galaxies: ISM –galaxies: spiral – infrared: ISM: continuum – stars: formation1. IntroductionNGC5195, the interacting companion of M51, is cataloged asan SB0 psc in the RSA catalog and as an SB0/a(r) by Thronsonet al. (1991). It is clearly distorted by its interaction with M51.Current views of the interaction between NGC5195 and M51have the companion passing perigalacticon