Program: GN-2007A-Q-25

Direct determination of the masses of supermassive black holes (hereafter SMBH) - via circumnuclear stellar kinematics - have been obtained essentially for nearby NON-ACTIVE galaxies. For most ACTIVE galaxies, such determinations have not been so far possible, due their larger distances, obscuration of the nuclear region and/or contamination by a nuclear source. The combination of the high spatial resolution of NIFS + Altair and the superb NIFS response in the K-band now allows resolving the radius of influence of the SMBH for a few nearby Seyfert galaxies, and to measure the stellar kinematics using the CO band heads around 2.3 microns, less affected by obscuration and by a blue nuclear continuum than optical stellar absorption features. We thus propose to measure the circumnuclear stellar kinematics and derive the SMBH mass of the closest Seyfert galaxies using NIFS. For this proposal we have selected NGC4258, because of: (1) its proximity, alowing to resolve the radius of influence of the nuclear SMBH, (2) its mild nuclear acitivity, which will minimize the effect of a nuclear continuum in the measurements, (3) it has a previous determination of the mass of the SMBH via gas kinematics - thus an ideal target to test the power of NIFS in resolving the radius of influence of the SMBH via circumnuclear stellar kinematics.