| Abstract | H I line observations with the Arecibo 305 m telescope were made of 23 galaxies within a 7 square degree region centered on the NGC 4005 group, a system of galaxies located in Zw 127-10. Accurate radial velocities and direct mass estimates derived from the 21 cm line profiles of the galaxies in this region are reported. A systematic trend in the radial velocities is found along the major axis of the NGC 4005 group. This correlation between position and velocity is fitted to a simple linear regression relation with a slope significantly different from zero. One explanation for this effect is that the NGC 4005 group is rotating with a period no longer than four billion yr. Other possible interpretations of this systematic effect are discussed. The mass of the group is estimated by applying the harmonic law, the virial theorem, and the projected mass method. The masses obtained from the three methods are all consistent. |
