The cosmological distance scale.

Abstract

A series of concentric focal-plane diaphragms has been used to investigate photoelectrically the distribution of light in typical Eo galaxies in the Leo group and the Virgo cluster (AX/X ~o.oo5) and in the Corona Borealis cluster (AX/~ = 0.072). In general these data show that galaxies extend far beyond the angular diameters normally assigned to them, and that their tenuous outer regions, which have not generally been included photometrically, contribute a substantial share of the total light. There seems, in fact, to be no measurable limit to these outer extremities. Since luminosity measurements for nearby galaxies have tended to be less inclusive than those for more distant galaxies, the present distance scale based on so-called total magnitudes contains a systematic error with distance. Not only is this source of error removed, but the whole problem of defining a system of magnitudes or angular diameters which would be free of systematic distance errors can be avoided if each galaxy is represented by a curve of integrated luminosity 1 as a function of angular diameter d instead of by a single magnitude or single diameter. When log 1 is plotted against log d for each of two similar galaxies, say, of similar rank in comparable clusters, their relative displacement can be graphically resolved into A log d and A log 1, the former providing a direct measure of the relative distances. After certain corrections, the amount by which A log 1 exceeds 2A log d is then a measure of effects due to recession and to apparent changes in absolute luminosity, via evolution and obscuration. Since the relationship of these quantities is the same for all cosmological models of general relativity,' and since recession is separately measurable, we thus have a direct hold on apparent changes in absolute luminosity. Preliminary results seem to indicate the existence of a rather large effect, which, if confirmed at distances beyond the Corona Borealis cluster, will lead to a major revision of the distance scale. I.H. P. Robertson, private communication. Mount Wilson and Palomar Observatories, Pasadena, Caltj.