Dynamics of Cosmic Flows

The editors suggested a review entitled "Are There Large-Scale Motions in the Universe?". The answer is "yes," in the sense that the interpretation of the data as motions is the simplest model, so far consistent with all other available data under the current "standard model" of physical cosmology. I review tests that could have ended up falsifying this model and failed, but the scope of this review is much extended as the field has developed far beyond the question of existence of motions. With the motions being accepted as a working hypothesis, the study of large-scale dynamics is becoming a mature scientific field where observation and theory are confronted in a quantitative way. It is this area of major activity in cosmology that is addressed here. I make no attempt to provide a complete reference list, nor do I try to achieve a balanced discussion of all the issues of relevance and authors involved. My goal is to provide a critical account of some of the issues in this field that I find important, with emphasis on theoretical implications. In many cases I quote only a recent paper automatically implying "and references therein." The reader is referred to a comprehensive, observation-oriented review of large­ scale motions in historical perspective by Burstein ( 1990b), a detailed review of distance indicators in a collection of essays by Jacoby et al ( 1992), and to Principles of Physical Cosmology by Peebles ( 1993). The current phase of the field was seeded by two major developments. One was the confirmation of the dipole moment in the Cosmic Microwave Back­ ground (CMB) (Corey & Wilkinson 1976, Smoot et al 1977), indicating via Doppler shift that the Local Group of galaxies (LG) is moving at rv600 Ian S-1 relative to the cosmological frame defined by the CMB. The other was the in­ vention of methods for inferring distances independent of redshifts based on intrinsic relations between galaxy quantities (Section 3; Tully & Fisher 1977,