Photometric and kinematic study of the barred spiral galaxy NGC 253

Detailed isophotometry of NGC 253 in the Sculptor Group in blue light to a limiting surface brightness of 29 magnitudes per square second has been obtained from a combination of photographic and photoelectric photometry. The standard photometric parameters have been derived; in particular, the total magnitude is B/sub T/ = 8.05, and the maximum detected dimensions are 60' x 26', or 44 x 19 kpc at the assumed distance of 2.5 Mpc. The absolute luminosity of NGC 253, corrected for galactic and internal extinction, is L/sub T/ = 2.65 x 1010 Lsub solar. A three-component luminosity model of NGC 253 is derived consisting of a r/sup 1/4/ spheroid, an exponential disk, and a spiral arm component which contribute, respectively, 15, 59, and 26 percent of the total B luminosity. A detailed velocity map has been derived from 9842 individual radial velocity measurements on 25 Hα interferograms covering the entire bright disk (20' x 5') of NGC 253. The rotation velocity reaches a nearly constant maximum of 205 km/s in the interval 3' < r < 10'. A total mass of M/sub T/ = 1.4 x 1011 Msub solar is estimated from the fit of several different mass models to the mean rotation curve. Noncircular motions, in excess of 50 km/s, are observed in several areas. These motions are not in agreement with the predictions of the linear density wave theory. The streaming motions within 200'' of the nucleus are similar to that predicted by a simple kinematic model of gas flow near a bar