The universality(?) of distance-indicator relations

Abstract

The origin of distance-indicator relations for galaxies is examined, as well as the possibility that they may vary with the large-scale environment. The relations reflect formative and evolutionary process of galaxies, and contain some information about them. They are expected to depend on the environment in a complex manner. There are hints that both the Tully-Fisher relation for the spirals, and the Dn-sigma relation for the ellipticals may depend on the parent cluster properties such as richness, velocity dispersion, or galaxy number density, but these tentative dependences are hard to separate from the selection effects. If the distance-indicators vary from one cluster to another, some of the large peculiar motions claimed in the literature are partly spurious. Until the environmental effects on distance-indicator relations are better understood, their use for the mapping of large-scale velocity fields and measurements of the far-field Hubble constant may be premature.

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