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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 emissionallows a very precise measurement of the central supermassive black hole mass($M_{\bullet}(maser) = 3.78 \pm 0.01 \times 10^7$ Mo). We analyse the emissionline properties and the stellar kinematics in a data cube of the central regionof NGC 4258, obtained, in the K band, with the Near-Infrared Integral FieldSpectrograph, at the Gemini-north telescope. The nuclear spectrum, after thestarlight subtraction, shows only the H$_2 \lambda 2.1218$ $\mu$m andBr$\gamma$ emission lines, the latter having a broad component withFWHM$_{Br\gamma}(broad) = 1600 \pm 29$ km s$^{-1}$. The spatial morphology andkinematics of the H$_2 \lambda 2.1218$ $\mu$m line are consistent with arotating molecular disc around the supermassive black hole, with an upper limitfor its diameter of 15.7 pc. The inner radio jet in this object is, inprojection, almost perpendicular to the H$_2$ emitting disc detected in thiswork, and also to the H$_2$O maser emitting disc. The main features of the mapsof the stellar kinematic parameters are well reproduced by a model of a thinrotating stellar circular disc. The supermassive black hole mass provided bythis dynamical modelling ($M_{\bullet}(disc) = 2.8 \pm 1.0 \times 10^7$ Mo) iscompatible, at 1$\sigma$ level, with the precise measurement resulting from theH$_2$O maser emission.

The molecular H2 and stellar discs in the nuclear region of NGC 4258