BVRI imaging of M 51-type pairs ^*

II. Bulge and disk parameters

Department of Astronomy, University of Oulu, PL 333 90571 Oulu, Finland e-mail: eija@koivu.oulu.fi

Send offprint request to: E. Laurikainen

Received: 2 September 1999
Accepted: 8 October 1999

Abstract

We present decompositions of azimuthally averaged surface brightness profiles in optical B, V, R and I-bands for a sample of 40 M 51-type interacting galaxies. The profiles were modelled by an exponential disk and a spherical bulge described either by the law or by an exponential function. Half of the galaxies were well fitted by both bulge models, whereas for the exponential function was a better choice. Special care was taken on eliminating superpositions of the companion galaxies. The mean B-band central surface brightness was found to be , which is near to the value originally found by Freeman (1970), but the scatter was fairly large. Galaxy interactions have strongly modified the disks in many of the galaxies in the sample. For example, six of them had extremely flat brightness profiles outside the exponential part of the disk, and many showed significant isophotal twists.