Faint Outer Regions of Elliptical Galaxies
Abstract
Photographs to faint limiting magnitudes have enabled isophotes of five elliptical galaxies to be traced to greater distances than previously. The giant ellipticals NGC 383, NGC 541, NGC 1275, NGC 4261, and NGC 4486 were found to extend to diameters of several tenths of a megaparsec. Somewhat smaller ellipticals in these groups have similar gradients, but spirals are sharply bounded. The faint luminosity in the outer regions is interpreted as being due to stars, probably dwarf stars predominantly. Since the density of matter in these regions is so low, it is concluded the stars were more likely to have been ejected from the center than condensed i siht. The results further indicate that in many clusters the outer regions of galaxies adjoin and that to some extent the cluster galaxies are imbedded in a common medium. With masses of E galaxies generally increased by an order of magnitude, the Oort limit of matter observable in galaxies should be raised toward a higher mean density for the average of observable space. The luminosities, masses, and 9)?/L ratios of the individual galaxies all increase when the usual computations are corrected for the presence of the outer regions. This correction then reduces the well-known discrepancy between 7L ratios for the average galaxy derived by applying the virial theorem to clusters of galaxies and the ?7L ratios derived from individual galaxies from rotation curves or velocity dispersions.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 1971
- DOI:
- 10.1086/150757
- Bibcode:
- 1971ApJ...163..195A