THE DENSITY AND PECULIAR VELOCITY-FIELDS OF NEARBY GALAXIES

We review the quantitative science that can be and has been done with redshift and peculiar velocity surveys of galaxies in the nearby unive rse. After a brief background setting the cosmological context for thi s work, the first part of this review focuses on redshift surveys. The practical issues of how redshift surveys are carried out, and how one turns a distribution of galaxies into a smoothed density held, are di scussed. Then follows a description of major redshift surveys that hav e been done, and the local cosmography out to 8,000 km s(-1) that they have mapped. We then discuss in some detail the various quantitative cosmological tests that can be carried out with redshift data. The sec ond half of this review concentrates on peculiar velocity studies, beg inning with a thorough review of existing techniques. After discussing the various biases which plague peculiar velocity work, we survey qua ntitative analyses done with peculiar velocity surveys alone, and fina lly with the combination of data from both redshift and peculiar veloc ity surveys. The data presented rule out the standard Cold Dark Matter model, although several variants of Cold Dark Matter with more power on large scales fare better. All the data are consistent with the hypo thesis that the initial density field had a Gaussian distribution, alt hough one cannot rule out broad classes of non-Gaussian models. Compar ison of the peculiar velocity and density fields constrains the Cosmol ogical Density Parameter. The results here are consistent with a flat universe with mild biasing of the galaxies relative to dark matter, al though open universe models are by no means ruled out.