PHOTOGRAPHIC MEASUREMENTS OF THE DIFFUSE LIGHT IN THE COMA CLUSTER.

Abstract

ABSTRACT The diffuse background light in the Coma cluster is measured using isodensity tracings of blue, green, violet and red photographic plates. The isodensity contours are calibrated using the star profile derived by Kormendy (1973). Between 4 and 14 arc min from the center, the surface brightness of the diffuse light decreases from about 26 to about 28 green magnitudes per arcsec squared. The total magnitude in this annulus is 11.22 (green magnitude), which is about 45% of the light in galaxies alone, or about 30% of the total. This does little to alleviate the 'missing mass' problem. The isodensity contours and the equivalent profile of the diffuse light closely parallel the distribution of light in galaxies, implying no strong mass segragation. However, the background light appears to be bluer than the galaxies. This is consistent with the hypothesis that the background consists of stars tidally stripped from galaxies, which generally become bluer at larger radii. Comparison of a variety of measurements shows that a reasonably consistent body of data on the background light now exists.