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NGC 4395 is a bulgeless spiral galaxy, harboring one of the nearest knowntype 1 Seyfert nuclei. Although there is no consensus on the mass of itscentral engine, several estimates suggest it to be one of the lightest massiveblack holes (MBHs) known. We present the first direct dynamical measurement ofthe mass of this MBH from a combination of two-dimensional gas kinematic data,obtained with the adaptive optics assisted near infrared integral fieldspectrograph Gemini/NIFS, and high-resolution multiband photometric data fromHubble Space Telescope's Wide Field Camera 3 (HST/WFC3). We use the photometricdata to model the shape and stellar mass-to-light ratio (M/L) of the nuclearstar cluster. From the Gemini/NIFS observations, we derive the kinematics ofwarm molecular hydrogen gas as traced by emission through the H$_2$ 1--0 S(1)transition. These kinematics show a clear rotational signal, with a positionangle orthogonal to NGC 4395's radio jet. Our best fitting tilted ring modelsof the kinematics of the molecular hydrogen gas contain a black hole with mass$M=4_{-3}^{+8}\times 10^5$ M$_\odot$ (3$\sigma$ uncertainties) embedded in anuclear star cluster of mass $M=2 \times 10^6$ M$_\odot$. Our black hole massmeasurement is in excellent agreement with the reverberation mapping massestimate of Peterson et al. (2005), but shows some tension with other massmeasurement methods based on accretion signals.

Measuring the mass of the central black hole in the bulgeless galaxy NGC 4395 from gas dynamical modeling