A catalog of 232 apparently interacting galaxy pairs of the M51 class is presented.
Catalog members were identified from visual inspection of multi-band images in the IRSA
archive. The major findings in the compilation of this catalog are (1) A surprisingly low
number of the main galaxies in M51 systems are early type spirals and barred spirals. (2)
Over 70% of the main galaxies in M51 systems are 2-armed spirals. (3) Some systems that
were classified as M51 types in previous studies are not M51 types as defined in this catalog.
There were a number of systems previously classified as M51 systems for which the
“companion” is identified as an HII region within the main galaxy or foreground star within
the Milky Way. (4) It was found that only 18% of the M51 type companions have redshift
measurements in the literature. There is a significant need for spectroscopic study of the
companions in order to improve the value of the catalog as a sample for studying the effects
of M51 type interaction on galaxy dynamics, morphology, and star formation. Further
spectroscopy will also help constrain the statistics of possible chance projections between
foreground and background galaxies in the catalog. The catalog also contains over 430
additional systems which are classified as “possible M51” systems. The reasons for
classifying certain systems as possible M51 systems are discussed.