Redshift-Distance Survey of Early-Type Galaxies. IV. Dipoles of the Velocity Field
Abstract
We use the recently completed redshift-distance survey of nearby early-type galaxies (ENEAR) to measure the dipole component of the peculiar velocity field to a depth of cz ~ 6000 km/s. The sample consists of 1145 galaxies brighter than m_B=14.5 and cz < 7000 km/s, uniformly distributed over the whole sky, and 129 fainter cluster galaxies within the same volume. The great majority of the Dn-sigma distances were obtained from new spectroscopic and photometric observations conducted by this project, ensuring the homogeneity of the data over the whole sky. For peculiar velocity analysis, galaxies have been assigned to groups/clusters using a well-defined criterion combined with information about groups objectively identified from the complete redshift surveys from which the ENEAR sample was drawn. In the present analysis, we consider a total of 1274 galaxies in 696 objects -- 282 groups/clusters and 414 isolated galaxies. We find that within a volume of radius ~ 6000$ km/s the best-fitting bulk flow has an amplitude of |vbulk| =149 +/- 41 km/s in the CMB restframe, pointing towards l=304 +/- 11 degrees, b=25 +/- 14 degrees only 30 degrees from the direction of the Local Group motion. This solution is in excellent agreement with that obtained by the SFI Tully-Fisher survey. Our results suggest that most of the motion of the Local Group is due to fluctuations within 6000 km/s, in contrast to recent claims of large amplitude bulk motions on larger scales.Keywords
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