The rich cluster in Perseus lies much nearer to the galactic plane than the Coma cluster, so has not been so well studied. Moreover it is not as symmetrical, the brightest galaxy members lying in an east-west line. It is possible that this projected line, which stretches for about 1°, is a transient effect observed in a cluster which is on the average much more symmetrical. A disc-shaped system seen nearly edge on is another possibility, although no rotation has been detected. The mean redshift of the Perseus cluster indicates a recession velocity of 5490 km s-1 and hence a distance of 72Mpc. Over 50 redshifts give a velocity dispersion of about 1400 kms-1, increasing in the core regions, the highest velocity dispersion yet recorded

Counts of galaxies in the Perseus cluster indicate a core radius of about 240 kpc, similar to that found in Coma, and indeed this seems to be a common value for rich clusters.

The core of the Perseus cluster is dominated by the Seyfert galaxy NGC1275. An extended radio source exists over much of the cluster and there are several interesting radio sources including the one (Perseus A) located at NGC 1275. The Perseus cluster is one of the brightest extragalactic X-ray sources, and this is again most probably due to radiation from hot gas at a temperature of about 108K. The extended X-ray emission is sharply peaked in the vicinity of NGC 1275.

The Perseus cluster contains several HEAD-TAIL RADIO SOURCES, the best studied example of which is NGC 1265. This lies about 0.5° (~1Mpc) from NGC 1275. As the radio map , extended emission can be traced for about 8 arc min north of the galaxy itself. This radio trail is itself double and there appear to be discrete blobs strung out in a semicircle which eventually merge into the tail. Radio polarization studies show that the magnetic field is aligned along the tail, and the degree of polarization itself increases with distance from the galaxy. The length of the tail (a few hundred kiloparsecs) seems to be similar to that expected from a source emitting synchrotron radiation and moving with a velocity of 1000 kms-1 or so. It is possible that we are viewing a radio trail, in which perhaps outbursts of activity from the galactic nucleus every few million years eject blobs of plasma that fall back from the galaxy, losing energy as they move through the cluster. Such an interpretation provides indirect evidence for the presence of an intracluster gas.

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