ISO observations of the interacting galaxy Markarian 297 with the powerful supernova remnant 1982aa

Markarian (Mkn) 297 is a complex system comprised of two interacting galaxies that has been modelled with a variety of scenarios. Observations of this system were made with the Infrared Space Observatory (ISO) using the ISOCAM, ISOPHOT and LWS instruments. ISOCAM maps at 6.7 µm, 7.7 µm, 12 µm and 14.3 µm are presented which, together with PHT-S spectrometry of the central interacting region, probe the dust obscured star formation and the properties of the organic dust. The ISOCAM observations reveal that the strongest emission in the four bands is at a location completely unremarkable at visible and near-IR (e.g. 2MASS) wavelengths, and does not coincide with the nuclear region of either colliding galaxy. This striking characteristic has also been observed in the overlap region of the colliding galaxies in the Antennae (NGC 4038/4039), the intragroup region of Stephan’s Quintet, and in IC 694 in the interacting system Arp 299, and again underlines the importance of infrared observations in understanding star formation in colliding/merging systems. At 15 µm, the hidden source in Mkn 297 is, respectively, 14.6 and 3.8 times more luminous than the hidden sources in the Antennae (NGC 4038/4039) and Stephan’s Quintet. Numerical simulations of the Mkn 297 system indicate that a co-planar radial penetration between two disk galaxies yielded the observed wing formation in the system about 1.5 × 10 8 years after the collision. A complex emission pattern with knots and ridges of emission was detected with ISOCAM. The 7.7 µm map predominantly shows the galaxy in emission from the 7.7 µm feature attributed to PAHs (Polycyclic Aromatic Hydrocarbons). The 14.3/7.7 µm ratio is greater than unity over most of the galaxy, implying widespread strong star formation. Strong emission features were detected in the ISOPHOT spectrum, while [O I], [O III] and [C II] emission lines were seen with LWS. Using data from the three instruments, luminosities and masses for two dust components were determined. The total infrared luminosity is approximately 10 11 L� ,w hich (marginally) classifies the system as a luminous infrared galaxy (LIRG). A supernova that exploded in 1979 (SN 1982aa) gave rise to one of the most powerful known radio remnants which falls close to the strongest mid-infrared source and is identified with star forming region 14 in the optical. This supernova explosion may have been accompanied by a gamma-ray burst (GRB), consistent with the idea that GRBs are associated with supernovae in star forming regions, and a search for a GRB consistent with the direction to Mkn 297, in satellite data from July to December 1979, is recommended.