1 DSM/DAPNIA/SAp, CEA-Saclay, 91191 Gif sur Yvette Cedex FRANCE
2 MPE, Garching, Germany
Located at 42 Mpc, Mkn 171 (Arp 299 = IC 694 + NGC 3690) is one of the nearest interacting galaxy system. By its proximity, and its intrinsic size, it provides good conditions to study the effects of star formation triggered by an interaction. In this object, four sources (called A, B, C and C') have been previously observed in several spectral ranges (near-infrared, radio and CO), two of them (A and B) being clearly associated with the nuclei of the main components of the system. However, the nature and the origin of the off-nuclear emissions in C and C' are not yet fully understood and more information is needed today to clarify these points.
For this purpose, we performed mid-infrared observations (5 to 16 microns) with the ISOCAM instrument in its spectro-imaging operating mode with a high spatial resolution (1.5"/pix). The images clearly show several sources associated with the ones previously identified in other spectral ranges. Spectral information indicates the presence of so-called PAH features in all the detected emitting regions, as well as forbidden lines of neon, silicate absorption and a continuum of varying strenght at higher wavelengths.
Variations of the spectral characteristics are used to identify the origin of the emission in the different regions as well as to determine the strength of the star formation activity and to describe the radiation field in the main regions.
Based on the comparison with other wavelengths, such as near-infrared emission, we will discuss the nature of each source present in the system and we will try to answer the open questions relative to this object: how many galaxies are involved in the interaction ? What is the nature of sources C and C' ? Does the system host any deeply embeded active nucleus ?