On the quiescence of the Hubble flow in the vicinity of the Local Group

A study using galaxies with distances from the Cepheid PL-relation

¹ CRAL -Observatoire de Lyon, 69561 Saint Genis Laval Cedex, France
² Tuorla Observatory, 21500 Piikkiö, Finland
³ Astronomical Institute, St. Petersburg State University, Staryj Petergoff, 198504, St. Petersburg, Russia

Corresponding author: T. Ekholm, timo@typhon.univ-lyon1.fr

Received: 8 December 2000
Accepted: 31 January 2001

Abstract

Cepheid distances of local galaxies (<7 Mpc) are used to study the very nearby velocity field, as pioneered by Sandage ([CITE]) who also pointed out its remarkable properties: linearity and quietness. The new data show that the velocity dispersion in the distance range as seen from the barycentre of the Local Group Mpc is as low as 38 km s^-1. The local rate of expansion coincides with the global Hubble constant. Down to 1.5 Mpc we cannot detect a deviation from the linear Hubble flow. This puts an upper limit for the mass of the Local Group, for a wide class of Friedman models, including those with the cosmological constant.