Evidence for a Massive Black Hole in the S0 Galaxy NGC 4342

Abstract

We have constructed axisymmetric dynamical models of the edge-on S0 galaxy NGC 4342: simple two-integral Jeans models as well as fully general, three-integral models using a modified version of Schwarzschild's orbit superposition technique. The two-integral models suggest a black hole (BH) of 3 or $6\times 10^8 M_\odot$, depending on the data set. The three-integral models can fit all ground-based and HST data simultaneously, but only when a central BH is included. Models without BH are ruled out at better than 99.73% confidence level. We determine a BH mass of $3.0^{+1.7}_{-1.0} \times 10^8 M_\odot$. This corresponds to 2.6% of the bulge mass, making NGC 4342 one of the galaxies with the highest BH mass to bulge mass ratio currently known.