Search

We have performed a series ofN-body experiments including the effects of a massive dominant background which follows Schuster's density law in order to simulate clusters of galaxies in which a smoothly distributed dark component is present. The existence of this background is inferred from the weak luminosity segregation observed in clusters which, however, show several characteristics of well-relaxed systems. The comparison of the velocity dispersion profiles of three clusters of galaxies (Coma, Perseus, and Virgo) with those obtained in the numerical experiments allows us to place some constraints on both the distribution and amount of distributed dark material in these clusters. The profiles are rather insensitive to variations in the ratio of the background mass to the mass attached to galaxies (Mb/Mg), but exhibit a strong dependence on their relative concentration. We conclude that highly concentrated background models are not consistent with observations. We find a maximum value for the ratio of the gravitational radius of the galaxies and the background (Rg/Rb) (approximately 0.6) and using previous results (Navarroet al., 1986) we conclude that virial theorem masses underestimate the total mass (Mb+Mg) of the clusters. As a final result, we derive a minimum value for theMb/Mg ratio. All these conclusions could apply in general if Coma, Perseus, and Virgo constitute a fair sample of the rich clusters of galaxies in the Universe.

Using the Uppsala General Catalog of bright galaxies and the northern and southern maps of the Lick counts of galaxies, statistical evidence of a morphology-orientation effect is found. Major axes of elliptical galaxies are preferentially oriented along the large-scale features of the Lick maps. However, the orientations of the major axes of spiral and lenticular galaxies show no clear signs of significant nonrandom behavior at a level of less than about one-fifth of the effect seen for ellipticals. The angular scale of the detected alignment effect for Uppsala ellipticals extends to at least theta of about 2 deg, which at a redshift of z of about 0.02 corresponds to a linear scale of about 2/h Mpc.

By means of statistical analyses on the Lick maps, the reported alignment effects of brightest cluster galaxies and ellipticals with the neighboring galaxy distribution, are confirmed. No peculiarities in the distribution around spirals and S0 were found, suggesting a lack of correlation of angular momentum with the neighboring galaxy distribution. It is found that the alignment signals are consistent with the presence of filaments or sheets of galaxies running across clusters and ellipticals rather than with a single overdensity on one side of these structures. 19 refs.

Using an independent sample of brightest galaxies in rich clusters in the southern galactic hemisphere, the Argyres et al. (1986) result that galaxy counts on scales to at least 15/h Mpc are systematically higher in the direction of the major axes of brightest cluster galaxies is confirmed.