The Galaxy Motion Relative to Nearby Galaxies and the Local Velocity Field

Details The Galaxy Motion Relative to Nearby Galaxies and the Local Velocity Field The Galaxy Motion Relative to Nearby Galaxies and the Local Velocity Field

Feb 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996aj....111..794k&link_type=abstract

Astronomical Journal v.111, p.794

Astronomy and Astrophysics

Astronomy

107

Local Group, Galaxies: Distances And Redshifts, Galaxies: Interactions

Scientific paper

We consider a sample of 103 galaxies with radial velocities V_0_ < 500 km s^-1^ and distances obtained by means of photometric distance indicators: Cepheids (n = 17), brightest stars (n = 69), and galaxy membership in the nearby bound groups (n = 17). Ranking the galaxies with their distance R we determine a running apex for the Sun, the Galaxy, and the Local Group as a function of R. For the solar apex with respect to the LG galaxies we obtain the parameters: {l_sun_ = 93^deg^+/-2^deg^, b_sun_ = -4^deg^+/- 2^deg^, V_sun_ = 316+/-5 km s^-1^}. That corresponds to a Galaxy center apex {l = 107^deg^, b = -18^deg^, v = 90 km s^-1^}, pointing at ~14^deg^ from M31. When the considered volume depth increases from 1.0-1.5 Mpc up to 4-8 Mpc, the solar apex drifts to {l_sun_ = 91^deg^, b_sun_ = 0^deg^, V_sun_ = 334 km s^-1^}, while the LG centroid apex shows a complicate wandering in a region {l = [40^deg^, 100^deg^], b = [0^deg^, +60^deg^]) with velocity increasing from 0 up to 40 km s^-1^, The running value for the local Hubble parameter, H(R), reaches the maximum (90+/-5) km s^-1^ Mpc^-1^ at R ~ 2 Mpc, and then decreases down to (70-65) km s^-1^ Mpc^- 1^. When both the Hubble component and the apex velocity are removed, the residual velocity field shows clear signs of anisotropy. Within the Local Supergalactic plane there is a prevalence of negative peculiar velocities towards the "+SGY" direction. This feature perhaps has the same origin as the "Local Velocity Anomaly" (LVA) known to exist over a scale of 10-30 Mpc. Besides the LVA, an excess of negative peculiar velocities is seen also along the SGZ axis and can be interpreted as if the expansion of the local pancake proceeds about 30% slower in the direction perpendicular to the symmetry plane than in the plane itself. Inside the Local Volume, galaxies possess a peculiar velocity dispersion of (72+/-2) km s^-1^ independent on the assumed volume depth. This value is almost the same for dwarf and giant galaxies: a behavior which has no simple explanations. The use of more precise solar apex parameters and the correction for the local anisotropy improves the use of radial velocities of nearby galaxies as distance indicators and allows to build a more accurate 3D map of the LV which reveals more "fine grain" structure details than Tully's catalog data.

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