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For refcode 1992A&A...260...17T:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
1992A&A...260...17T Investigations of the Local Supercluster velocity field I. Observations close to Virgo, using Tully-Fisher distances and the Tolman-Bondi expanding sphere P. Teerikorpi, L. Bottinelli, L. Gouguenheim and G. Paturel Tuorla Observatory University of Turku, SF-21500 Piikkio, Finland DERAD, Observatoire de Paris, Section de Meudon, F-92l95 Meudon Cedex, France Universite Paris XI, F-91405 Orsay Cedex, France Observatoire de Lyon, F-6956l Saint-Genis Laval Cedex, France Received July 22, accepted November 12, 1991 Abstract. We have investigated the velocity-distance relation close to the direction of the Virgo cluster, with distances from the Tully-Fisher relation, and with attention to the Malmquist bias. For {THETA} > 8^deg^ a behaviour is releaved which is as expected from the Tolman-Bondi solutions for an expanding spherical mass distribution, previously discussed by Tully & Shaya (1984; hereafter TulSha) using a smaller sample of galaxies. (1) Various density distributions, constrained by the mass inside the Local Group distance (required to produce V_Vir_), agree with the observations, but only if the mass within the Virgo 6^deg^ region is close to or larger than the standard Virgo virial mass values. This is so independently of the value of q_0_, of the slope of the density distribution outside of Virgo, and of the values adopted for Virgo distance and velocity. The v vs. d relation (velocity and distance from the Virgo centre) shows directly that the "zero-velocity surface" lies at d ~ 0.45. (2) Generally, the observations imply that the central 6^deg^ mass has the standard M (virial) as a rough lower limit. From this it follows, together with the light ratios within the local supercluster and the light enhancement relative to the general field, that light does not trace mass. Analysis of the data below {THETA} = 8^deg^ and inside the standard 6^deg^ circle led to the following conclusions: (3) The Tolman-Bondi behaviour may be discerned close to the Virgo centre, producing high velocities V_0_ > 2000 km s^-1^ for infalling galaxies with distances somewhat smaller than the Virgo distance. (4) An expanding component, as proposed by de Vaucouleurs (1982), causes the negative velocities for several galaxies nearer than r_vir_. Hydrogen-deficient galaxies prefer this expanding component, and there is evidence that H I deficiency causes underestimates of Tully-Fisher distances, e.g. transferring negative-velocity galaxies too much to the foreground. (5) Background contamination produces an asymmetrical distribution of velocities behind r_vir_ (behind the high-velocity expanding component). Hence, the large Spiral velocities in the Virgo cluster, V_0_ > 1800 kms^-1^, can be ascribed to three origins: TB infall, expanding component, Malmquist-biased background. Small velocities are mostly due to the expanding component. (6) The dynamical components of the Virgo region are differently distributed in the sky. The expanding component has a flattened distribution along the line M 87/M 84 - M 59. The infalling high-velocity galaxies show a distribution which is a continuation into the 6^deg^ circle of the Southern Extension infall previously suggested by TulSha. The other spirals do not show a concentration in the 6^deg^ circle. (7) The tight angular concentration of negative-velocity galaxies can be understood by a combined effect of projection and a quick deceleration of the initial high expansion velocities (when the central mass is high enough, close to that required by the TB inflow). Key words: cosmology - Hubble law - clusters of galaxies
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