NGC 4258 is an SABbc Seyfert galaxy , located at a distance of 7.2 \pm 0.3 Mpc .
This object is well known by its nearly edge-on molecular nuclear disc , located between 0.16 and 0.28 pc from the nucleus , whose H _ { 2 } O maser emission allows a very precise measurement of the central supermassive black hole mass ( M _ { \bullet } ( maser ) = 3.78 \pm 0.01 \times 10 ^ { 7 } M _ { \sun } ) .
We analyse the emission line properties and the stellar kinematics in a data cube of the central region of NGC 4258 , obtained , in the K band , with the Near-Infrared Integral Field Spectrograph , at the Gemini-north telescope .
The nuclear spectrum , after the starlight subtraction , shows only the H _ { 2 } \lambda 2.1218 \mu m and Br \gamma emission lines , the latter having a broad component with FWHM _ { Br \gamma } ( broad ) = 1600 \pm 29 km s ^ { -1 } .
The spatial morphology and kinematics of the H _ { 2 } \lambda 2.1218 \mu m line are consistent with a rotating molecular disc around the supermassive black hole , with an upper limit for its diameter of 15.7 pc .
The inner radio jet in this object is , in projection , almost perpendicular to the H _ { 2 } emitting disc detected in this work , and also to the H _ { 2 } O maser emitting disc .
The main features of the maps of the stellar kinematic parameters are well reproduced by a model of a thin rotating stellar circular disc .
The supermassive black hole mass provided by this dynamical modelling ( M _ { \bullet } ( disc ) = 2.8 \pm 1.0 \times 10 ^ { 7 } M _ { \sun } ) is compatible , at 1 \sigma level , with the precise measurement resulting from the H _ { 2 } O maser emission .