Evidence for a supermassive object in the nucleus of the galaxy M87 from SIT and CCD area photometry

Abstract

Two-dimensional SIT and CCD detectors have been used to measure the surface brightness of the peculiar elliptical radio galaxy M87. Measurements were made in three broad-band colors (B, V, and R) to a distance of 80" from the nucleus, with 1" spatial resolution and photometric accuracy of the order of 1%. The data are given in some detail and are compared with earlier photographic results. The most obvious feature of the data is a bright, barely resolved central luminosity spike, which is not seen in similar data on other nearby normal ellipticals. Also, attempts to fit isothermal or King models away from the nuclear spike show additional excess luminosity in the central regions of the galaxy (r < 10"), which cannot be fitted by such a model. A model-independent dynamical analysis, using the photometric data combined with spectrographic results by Sargent et al., shows that the nucleus of M87 contains a compact mass of low luminosity, with M = 5 x 10^9 M_⊙, r < 100 pc, and M/ℒ > 60. All of the existing data is well fitted by a King model containing a central black hole of mass M = 3 x 10^9 M_⊙ and a point luminosity source. While such a model is not uniquely required by the data, it is perhaps the most plausible of several possible models considered. At present, M87 is probably the best case for a hypothetical massive black hole in a galaxy nucleus.

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