The Pisces-Perseus Supercluster and Gravitational Quasi-Equilibrium Clustering

Details The Pisces-Perseus Supercluster and Gravitational Quasi-Equilibrium Clustering The Pisces-Perseus Supercluster and Gravitational Quasi-Equilibrium Clustering

Dec 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...509..595s&link_type=abstract

The Astrophysical Journal, Volume 509, Issue 2, pp. 595-607.

Astronomy and Astrophysics

Astronomy

8

Galaxies: Clusters: Individual (Pisces-Perseus), Gravitation

Scientific paper

We analyze the three-dimensional spatial-velocity distribution of the counts-in-cells for 4501 galaxies in the Pisces-Perseus supercluster. This is done for the total sample, for a subset containing the most conspicuous galaxies (brightest members with large intrinsic linear diameters), and for a subset containing the least conspicuous galaxies (faintest members with small intrinsic linear diameters). We also examine subsets limited by absolute magnitudes as well as volume limited samples. The counts-in-cells distribution functions for all these samples are described remarkably well by the gravitational quasi-equilibrium distribution which was previously found to fit the more statistically homogeneous Zwicky, CfA, ESO, and IRAS catalogs. For the complete Pisces-Perseus sample, the value of b, representing the ratio of gravitational correlation energy to the kinetic energy of peculiar motions is 0.8. The most conspicuous galaxies are somewhat more uniformly distributed than the least conspicuous ones which tend to follow the overall distribution. A dendrogram analysis shows that groups of the most conspicuous galaxies tend to be located near groups of the least conspicuous ones. We also analyze the velocity distribution in different parts of the supercluster. There is a dense core of about 750 galaxies which have an overall Gaussian velocity distribution with a dispersion of about 450 km s^-1 around the mean of 5260 km s^-1. However this region is not completely relaxed since it contains subgroups which may not have Gaussian distributions. Moreover, in most subgroups the crossing time exceeds the Hubble time, indicating incomplete relaxation. Irregular galaxies tend to concentrate in this region, perhaps indicating significant tidal interactions. Spatial distribution functions measured for increasing numbers of galaxies around the dense core of Pisces-Perseus approach the form and have the value of b observed in larger statistically homogeneous catalogs. It appears that >~10^3 galaxies in this region constitute a ``fair sample'' with a wide range of structures characteristic of gravitational clustering. Our results appear consistent with the supercluster forming gravitationally as an accumulation of smaller clusters. Accurate peculiar velocities of these galaxies would help decide whether this clustering was stimulated by a larger scale perturbation or occurred by chance.

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