Shock Excitation in Interacting Galaxies: Mkn 266

Abstract

We present near infrared data on the luminous interacting system Mkn 266 (NGC 5256), comprising 2um continuum, and Br_gamma and 1-0S(1) emission line images, together with K-band spectra. We have fitted stellar templates to the continuum, allowing us to account for all the stellar features and hence detect even faint gas excitation emission lines, including 8 and 11 H_2 lines in the SW and NE nuclei respectively. Population diagrams for the excited H_2 molecules indicate that most of the 1-0S(1) in each of the nuclei has a thermal origin. We discuss this with reference to the observed morphologies, especially that of the 1-0S(1) line. In particular, the core of 1-0S(1) in the NE nucleus is more compact than the 2um continuum; while in the SW nucleus the 1-0S(1) is significantly offset by 500pc from the continuum (and other) emission. Lastly we address the issue of the region midway between the two nuclei, where previously a strong source of radio continuum has been observed. These results are set in the context of interacting galaxies where shock excited emission might be expected to occur as a direct consequence of the interaction.