The density and peculiar velocity fields of nearby galaxies

Abstract

We review the quantitative science that can be and has been done with redshift and peculiar velocity surveys of galaxies in the nearby universe. After a brief background setting the cosmological context for this work, the rst 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 eld, are discussed. Then follows a description of major redshift surveys that have 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 second half of this review concentrates on peculiar velocity studies, beginning with a thorough review of existing techniques. After discussing the various biases which plague peculiar velocity work, we survey quantitative analyses done with peculiar velocity surveys alone, and nally with the combination of data from both redshift and peculiar velocity 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 hypothesis that the initial density eld had a Gaussian distribution, although one cannot rule out broad classes of non-Gaussian models. Comparison of the peculiar velocity and density elds constrains the Cosmological Density Parameter. The results here are consistent with a at universe with mild biasing of the galaxies relative to dark matter, although open universe models are by no means ruled out.

Galaxy clusters in the Perseus-Pisces region -- II. The peculiar velocity field

“…Following Strauss & Willick (1995), we refer to this procedure as 'Method I'. In this section we describe the FP fits.…”

“…The PP supercluster is at least as overdense in galaxies if not more so than the GA (Saunders et al 1991;Hudson 1993;Strauss & Willick 1995). If PP is as massive as implied by its overdensity in galaxies, then strong infall of galaxies into the PP supercluster is predicted.…”

“…The use of a cluster sample minimises the Malmquist bias problems which plague field samples (Strauss & Willick 1995). Furthermore, since the cores of clusters are rich in early-type galaxies, cluster-elliptical samples are less prone to contamination than spiral samples.…”

Can the Tully-Fisher Relation Be the Result of Initial Conditions?

“…Many di erent e ects contribute to this error budget. Observational errors are usually estimated to be 0.15{0.30 mag (Strauss & Willick 1995), with a signi cant contribution coming from the measurement of the HI line widths. The ellipticity of the halo potential leads to error in measuring the circular velocity and estimating the inclination of the baryonic disk (Franx & de Zeeuw 1992); these e ects have been measured in a sample of spirals and estimated to contribute a scatter of about 0.15 mag (Rix & Zaritsky 1995).…”

Fractal structures and the large scale distribution of galaxies

“…In such a situation all the estimations of the density parameter at smaller scales based on the linear approximation 43 , and hence based on the untested assumption of linearity, are not correct. We have studied in detail 24 the gravitational force distribution in a fractal structure.…”