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Session 8 - Distance Indicators.
Display session, Monday, January 15
North Banquet Hall, Convention Center
The Tully-Fisher and D_n - \sigma techniques are most commonly used to obtain redshift-independent estimates of galaxy distances. In some cases, however, the two methods yield conflicting results. The most notorious of such cases refers to the cluster of galaxies Abell 2634: while the Tully-Fisher relation applied to a sample of 11 spiral galaxies gave a distance estimate corresponding to essentially zero peculiar velocity, the D_n - \sigma relation applied to a sample of 18 elliptical and lenticular galaxies gave a distance estimate corresponding to a peculiar velocity of --3400 km s^-1. This difference has been used as evidence for the possible non-universality of the two relations, which would result in spurious peculiar velocities, and, in turn, in inadequate reconstructions of the local Universe mass density field.
As part of a larger project to compare Tully-Fisher and D_n - \sigma redshift-independent distance estimates for nearby clusters of galaxies, we have obtained I band CCD photometry, and either 21cm line rotational velocities (for spirals) or Mg lines internal velocity dispersions (for E and S0's) for a large sample of galaxies in the region of A2634 (45 spirals and 52 E and S0's). This data-set, combined with a detailed study of cluster membership, is used to obtain an accurate determination of the distance to A2634.
