NGC 4736 (M94). - Chincarini and Walker (1967) have published a series of short exposures of NGC 4736 taken with the Lick 120-inch (3-m) telescope. They report that spiral arms may be traced in to a radius of 7" from the center. The features defining the central spiral pattern are the dust lanes.
Sandage (1961) discusses the remarkable range in surface brightness exhibited by this galaxy. An equally remarkable feature is the presence of a zone of very bright HII regions. In contrast to the 6563 photograph is a longer-exposure photograph taken in the continuum, 6650, and showing the amorphous central region with clearly defined dust lanes. A recent 200-inch (5-m) H photograph has been published by van der Kruit (1974).
One unusual characteristic of this galaxy is the difficulty in identification of the HII regions with stars on the blue photograph. These regions are apparently embedded in the dust lane and appear very faint (if at all) on the blue photograph.
The marked asymmetry of the dust suggests that the northeastern side of the galaxy is the near one. This, combined with the very regular rotation curve found by Chincarini and Walker, indicates a spiral with trailing arms.
Chincarini and Walker have found a distinctive dip in the rotation curve about 30" from the nucleus in position angles 123° and 107°. The location of the dip is just to the inside of the ring of bright HII regions, but it is not clearly coincident with the strong dust lanes.