ABSTRACT

Arp 86 is studied in terms of 3-dimensional N-body simulations and compared to CCD-observations. Deep, high resolution BVRI images were obtained in order to determine initial parameters for dynamical modelling, and to study star formation properties of these galaxies. The models suggest that the companion galaxy is moving in a low inclination, low eccentrity orbit thus performing several revolutions around the main galaxy, the obtained colors being in agreement with this interpretation. The orbit geometry favors material transfer between the components, which is proposed to be the cause of the anomalously large activity in the companion, and of the ongoing star formation in the bridge. The prolonged perturbation due to dynamically bound companion explains the grand-design structure of the main galaxy.

OBSERVATIONS AND N-BODY MODEL

Arp 86 (NGC 7753/54) is a spiral pair resembling M51 system. In order to study its star formation properties deep, high resolution BVRI CCD-photometry has been obtained (Laurikainen et al. 1993). Same observations are utilized in determination of initial parameters for dynamical modelling.

Dynamical modelling of the pair is performed with a new fast N-body code (Salo and Laurikainen 1993), capable of following the simultaneous evolution of two or more systems including both stellar and gaseous components. In the code galaxy disks are described in terms of self-gravitating particles, while analytical models are used for the spherical halo components. Potential evaluation is based on multiple, comoving logarithmic spherical potential grids. The code is 3-dimensional and thus allows arbitrary orbital geometry, and retains good spatial resolution simultaneously near the nuclei of both systems as well as in the interaction zone.