Spectra and Other Characteristics of Interconnected Galaxies and of Galaxies in Groups and in Clusters. III.
Abstract
An observational and theoretical analysis of the medium compact cluster of galaxies around NGC 541 has been initiated. The cluster, in an area of four square degrees, contains about five hundred galaxies whose apparent photographic magnitudes lie in the range 13A <[rn < 19.0. The positions and magnitudes of eighty-five cluster members have been determined. Their distribution confirms the exponential luminosity function which was previously established from the study of the populations of 704 rich clusters of galaxies. The surface brightness of the above-mentioned cluster galaxies is plotted in dependence upon their magnitudes, indicating both decreasing and increasing surface brightness with increasing magnitude. This is related to the discovery, recently made, of a relatively great number of very compact and absolutely faint galaxies. Structural and spectral types of the galaxies of the cluster studied are remarkably uniform, pointing to a very old age and a stationary character of the cluster. The average symbolic velocity of recession of forty-one cluster galaxies is (Vs) = 5321 km/sec and the dispersion ((A V5) 2)112 is 406 km/sec. From the analysis of the spatial distribution of the values of V it follows that the cluster is not sensibly rotating, although it is elliptical in shape. From the spatial distribution of the values of the velocity dispersion it may be concluded that the cluster is not expanding. The fact that the fainter galaxies have a greater velocity dispersion than the brighter galaxies indicates a tendency toward the establishment of equipartition of energy among at least the brighter cluster galaxies. The indicative distance of the cluster, the indicative absolute photographic magnitude of its brightest member galaxy and the relative indicative mass4uminsity ratio, as determined from the Virial theorem, are respectively, D* = 53.2 million pc, M* = -20.2 and )? 100. This value of lies midway between those found for individual bright galaxies and those of very richly populated compact clusters of galaxies. Suggestions are discussed of how might be found to be drastically reduced because of the presence of various types of as yet undetected types of intergalactic matter. For the past four years the cluster around NGC 541 has been searched for supernovae with the 48-inch Schmidt telescope. As a result of this search one supernova of Type I has been found in the member galaxy IC 1703 of the cluster on January 22, 1963.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 1964
- DOI:
- 10.1086/147752
- Bibcode:
- 1964ApJ...139..269Z