Rotation curves, mass distributions and total masses of some spiral galaxies.

Summary. Six spiral galaxies which are almost "edge on" were observed with the 3:2, 1420 MHz beam at the Arecibo Observatory, and neutral hydrogen was detected out to more than 10' from the center in each galaxy. Flat rotation curves (outside the central regions) were obtained in all six cases with one possible exception. The (differential) mass-to-light ratio must increase considerably with distance from the cent. The minimum t tal m ss for NGC 4565 is 8xlO M0x (60 km 5 Mpc /H0). Key words: rotation curves - masses - spiral galaxies.