HI observations of galaxies in a catalog of nearby galaxies. II. The motion of the sun and the galaxy and the velocity dispersion of 'field' galaxies.
Abstract
Relative distances to a complete sample of nearby galaxies with corrected radial velocities of <500 km s-1 determined via the blue Tully-Fisher relation are used to redetermine the vector of the solar motion, the parameters of the Virgocentric flow model, and the velocity dispersion of field galaxies. We attempted to separate the different kinematical effects. Based on a total of 25 galaxies the motion of the sun with respect to Local Group members is found to be 311 km s-1 toward an apex at l11 = 99.°2 and b11 = -3.°4 in quite good agreement with earlier solutions. The residual r.m.s. velocity scatter of galaxies in the Local Group is then found to be 47 km s-1. With a local Hubble ratio of 1± 13 km s-1 Mpc-1 the Local Group appears to be bound. Using all available 135 non-Local Group galaxies in the velocity-restricted sample reveals a clear flow pattern. The apex of the flow lies at l11 = 272.°4 and b11 = 58.°9 and at a distance equal to that of the Virgo cluster. The apex is roughly 16° away from the centre of the Virgo cluster toward the direction of the Hydra I cluster. The formal value of the Virgocentric velocity of the Local Group is 367 ± 55 km s-1. The detection of a nearly pure Virgocentric motion leaves unexplained a large component of the motion toward the microwave background radiation dipole. In agreement with earlier results this component can only be explained on the assumption of a comoving volume considerably larger than the one considered here. The centroid of the Local Group has a peculiar motion above and beyond the Virgocentric streaming velocity of 80 km s-1 towards l11 = 325° and b11 = -70°; this result has a formal significance of 5. The significance vanishes, however, if the uncertainty of the velocity reduction to the centroid of the Local Group is allowed for; any remaining error of the adopted reduction perpetuates as a systematic, direction-dependent velocity error of the sample galaxies, leading thus to a spurious peculiar motion of the Local Group. For the peculiar, one-dimensional velocities of nearby field galaxies a generous upper limit can be set of 117 km s-1.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- January 1987
- Bibcode:
- 1987A&A...171...33R
- Keywords:
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- Astronomical Catalogs;
- Galactic Structure;
- Hydrogen Clouds;
- Local Group (Astronomy);
- Solar Rotation;
- Virgo Galactic Cluster;
- Background Radiation;
- Elliptical Galaxies;
- Microwaves;
- Milky Way Galaxy;
- Radial Velocity;
- Astrophysics