The rotation curves and mass distributions of the close pair of spiral galaxies NGC 935 and IC 1801

Spectroscopic observations of NGC 935 and IC 1801, a close pair of spiral galaxies, are described. The corrected radial velocity of NGC 935 is 4290 km/s, corresponding to a distance of 79 Mpc, which is taken as the distance of the pair. No large scale non-circular motions are present in either galaxy despite their apparent proximity. The 'rotation curve' of NGC 935 extends as far as IC 1801 but is distorted beyond 26 seconds (10 kpc) from the nucleus. The mass interior to this radius is 5.3 x 1010 solar masses. The total mass is estimated to be 8 x 1010 solar masses. IC 1801 displays a linear rotation curve and estimates of the nuclear mass from barred and non-barred models are 1.3 x 1010 solar masses and 1.8 x 1010 solar masses. The barred model is preferred. Approximate mass to luminosity ratios lie in the range 2.6 < M/L < 4.0 for NGC 935, and 1.5 < M/L < 2.0 for IC 1801. No missing mass is required for the system to be bound, but a circular orbit is improbable. (author)