A Stellar Dynamical Mass for the Central Black Hole in MCG$-$06-30-15

Abstract: We present the stellar dynamical mass of the central black hole in the nearby Seyfert galaxy MCG$-$06-30-15 using the Schwarzschild orbit-superposition method implemented in the open-source code FORSTAND. We obtained spatially resolved $K$-band nuclear stellar spectra for this galaxy with SINFONI on the VLT. We extracted the bulk stellar kinematics using Gauss$-$Hermite (GH) parameterization of the line-of-sight velocity distributions. A multicomponent surface brightness profile of the galaxy was determined from an $HST$ medium-band $V$ image. Our best-fit models indicate a black hole mass of $M_{BH}=(4.4\pm1.4) \times 10^7 M_{\odot}$ and a stellar mass-to-light ratio of $M/L$=($3.0\pm0.3$) $M_{\odot}$/$L_{\odot}$, within 1$\sigma$ confidence intervals. Our constraint on $M_{BH}$ agrees with an upper limit on the mass from stellar dynamics based on the Jeans Anisotropic Method, but is $\sim$10 times larger than the reported mass from reverberation mapping. However, our best-fit $M_{BH}$ may be systematically biased high due to the counter-rotating disk in the nucleus of MCG$-$06-30-15 and the inability of the GH parameterization to fully describe such a complicated set of stellar kinematics. In addition, a dynamical $M_{BH}$ value depends heavily on the assumed source distance, which is not yet accurately constrained for this galaxy. MCG$-$06-30-15 is only the fourth galaxy in which we can compare $M_{BH}$ from stellar dynamical modeling with that from reverberation mapping. A direct comparison of $M_{BH}$ allows us to identify and investigate the possible sources of bias associated with different mass measurement techniques, which may influence our understanding of black hole and galaxy coevolution across cosmological timescales.