ON THE MOTION OF THE LOCAL-GROUP AND ITS SUBSTRUCTURES

We consider the problem of the relative motion both of the substructur es of the Local Group of galaxies (revealed via the S-tree method), an d of the velocity of the Local Group itself. The existence of statisti cally significant bulk flow of the Milky Way subsystem is shown via a 3D reconstruction procedure, which uses information on the radial velo cities of the galaxies but does not take account of their distances. O nce the bulk motion of the substructures is estimated we also consider , in combination with the observed cosmic microwave background (CMB) d ipole, the mean velocity of the Local Group itself. Assigning to the L ocal Group the mean motion of its main substructures, we evaluate its peculiar velocity in Milky Way frame VLG-->MW = (-7 +/- 303, -15 +/- 1 55, + 177 +/- 144) or 178 km s(-1) toward galactic coordinates l = 245 and b = +85. Combined with the CMB dipole VMW-->CMB, we obtain a Loca l Group velocity in CMB frame: VLG-->CMB = (-41 +/- 303, -497 +/- 155, 445 +/- 144) or 668 km s(-1) towards l = 265 and b = 42. This estimat ion is in good agreement, within the 1 sigma level, with the estimatio n of Yahil et al.