Three-integral multicomponent dynamical models and simulations of the nuclear star cluster in NGC 4244

Adaptive optics observations of the flattened nuclear star cluster in the nearby edge-on spiral galaxy NGC 4244 using the Gemini near-infrared integral field spectrograph (NIFS) have revealed clear rotation. Using these kinematics plus 2MASS photometry, we construct a series of axisymmetric two-component particle dynamical models with our improved version of nmagic, a flexible χ2-made-to-measure code. The models consist of a nuclear cluster disc embedded within a spheroidal particle population. We find a mass for the nuclear star cluster of within ∼42.4 pc (2 arcsec). We also explore the presence of an intermediate-mass black hole and show that models with a black hole as massive as are consistent with the available data. Regardless of whether a black hole is present or not, the nuclear cluster is vertically anisotropic (β z < 0), as was found with earlier anisotropic Jeans models. We then use the models as initial conditions for N-body simulations. These simulations show that the nuclear star cluster is stable against non-axisymmetric perturbations. We also explore the effect of the nuclear cluster accreting star clusters at various inclinations. Accretion of a star cluster with mass 13 per cent that of the nuclear cluster is already enough to destroy the vertical anisotropy, regardless of orbital inclination.