INDICATIONS OF DARK MATTER DERIVED FROM LARGE SCALE FLOWS

Marc Davis, Adi Nusser

Published 1995-01-09Version 1

Recent progress in the measurement of relative distances to galaxies has been quite substantial, and catalogs of 3000 galaxies with distances are soon to become available. The peculiar {\it velocity} field (deviations from Hubble flow) derivable from these catalogs, when compared to the peculiar {\it gravity} field derived from all sky redshift surveys of galaxies such as the 1.2Jy IRAS survey, leads to a unique and extremely powerful test of the density parameter $\beta \equiv \Omega^{0.6}/b_I$, where $b_I$ is the possible linear bias of the IRAS selected galaxies relative to the mass fluctuations. We review the status of these large scale flow measurements and present a new methodology to describe the two fields by means of an expansion in a set of orthogonalized functions describing a general potential flow to any chosen resolution. The parameters of the flow can be estimated by minimization of the $\chi^2$ describing the scatter of observed versus predicted linewidths from an inverse Tully-Fisher relation. By this method one can intercompare the gravity and velocity fields coefficient by coefficient, deriving a precise fit for the density parameter and an assessment of the degree of coherence between the fields. The present situation is transitory-- different analyses of the same data are not yielding consistent results. Until this embarassment is untangled, estimates of $\beta$ should be taken with a large grain of salt.