NGC 4258: A compact central infrared source revealed

We present high-resolution (similar to 0.'') near-infrared Keck observations that probe the optically obscured nucleus of NGC 4258 (M 106), which is believed to contain a 3.6 x 10(7) M. black hole. The images show a compact central source at K (2.21 mu m) and H (1.65 mu m). To determine the strength of the compact component against the stellar background, we normalized the J (1.25 mu m) surface brightness profile, which is taken to be dominated by the bulge stars, to the K and H profiles at 200 pc and subtracted it out. The normalization constant in each case agrees well with the outer colors of highly inclined spirals. The compact source has a measured K flux of 4.5 mJy and an H flux of 1.1 mJy. After making reasonable assumptions about the intrinsic energy distribution of the central source based on optical polarimetry and X-ray measurements, we derive a reddening to the source of A(v) similar to 17 mag. When corrected for this extinction, the IR (1.5-3.5 mu m) luminosity is similar to 2 x 10(7) L.. The corresponding X-ray (2-10 keV) luminosity is similar to 10(7) L., while the central source has been estimated at similar to 10(2), L. in the radio. We suggest on the basis of the polarimetric evidence that the source of the near-infrared excess is nonthermal, although the possibility of thermal emission by dust grains in the inferred torus cannot be ruled out.