Luminosity distribution in the central regions of Messier 87 - Isothermal core, point source, or black hole

Abstract

A combination of photographic and photoelectric photometry with the McDonald 2 m reflector is used to derive a precise mean luminosity profile (r *) of M87 (jet excluded) at 0"6 resolution out to r * = 70". Within 8" from the center the luminosity is less than predicted by extrapolation of the r11 law defined by the main body of the galaxy (8" < r * < 240"), but is in excess of an isothermal core model best fitted in the interval 6" < r * < 20". This central spike cannot be explained simply by adding a nonthermal point source to an isothermal core model, or by adding only a central point mass (black hole?). It is well represented by the sum of a modified isothermal core model having both a central point mass and a central point source. At a revised distance A = 12.6 Mpc ( o = 30.5) the structural length ofthe underlying isothermal is a = 2"78 = 170 pc, the mass of the "black hole" = 1.7. 10 and the luminosity of the point source (B0 = 16.95, M0 = - 13.55) equals 4.2% of the integrated luminosity B(6") = 13.52 of the galaxy within r * = 6". These results agree closely with and confirm the work of the Hale team. Comparison of the McDonald and Hale data suggests that the central source may have been slightly brighter ( 0.5 mag) in 1964 than in 1975-1977. Subject headings: black holes - galaxies: individual - galaxies: nuclei - galaxies: photometry - galaxies: structure