Doppler-shift distributions. I. Extragalactic Peculiar motions

Journal Article · Fri Jul 15 04:00:00 EDT 1977 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/155371· OSTI ID:7304666

Gross, P G

Starting with an isotropic Maxwellian velocity distribution with arbitrary mean motion, the first four moments of the Doppler-shift distribution are computed as functions of (1) the Hubble velocity in an isotropic, homogeneous universe, (2) the velocity dispersion in the center of mass frame, and (3) the peculiar velocity associated with the mean motion. The formulae obtained are correct to second order in the velocities normalized to the speed of light with respect to the fundamental frame at the time and place of the universe where the observed photons were emitted.A brief application of the formulae to clusters of galaxies with an isothermal velocity distribution leads to the following: (a) the velocity dispersion of the galaxies within the cluster is essentially unaffected by the peculiar motion of the center of mass of the cluster; (b) the higher order moments of the distribution of redshifts for a cluster can be combined to depend only on the mean peculiar motion of the cluster; however, the accuracy of the available observations provides only a consistency check with the assumption of isothermality; (c) the approximate dispersion of peculiar motions for redshifts <0.03 is approx. +- 650 km s/sup -1/; this is equivalent to a dispersion in absolute magnitude of approx. +- 0.28 mag, or a formal dispersion in the Hubble constant of approx. +- 7 km s/sup -1/ Mpc/sup -1/; (d) anisotropies in antipodal sample means of approx.550 km s/sup -1/ for the redshift range of 3500--6500 km s/sup -1/ are consistent with a patchy intergalactic extinction of A/sub v//sup 0.02/approx. =2.0 mag Gpc/sup -1/, caused by a patchy dust distribution of density N (intergalactic)/N (interstellar) approx. =4 x 10/sup -6/.

• Research Organization: Warner and Swasey Observatory, Case Western Reserve University
• OSTI ID: 7304666
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 215:2; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics &amp; Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COSMOLOGY
DISTRIBUTION
DOPPLER EFFECT
GALAXY CLUSTERS
HUBBLE EFFECT
INTERGALACTIC SPACE
RED SHIFT
SPACE
UNIVERSE
VELOCITY