We have used a near-infrared nuclear spectrum ( covering the Z , J , H and K bands ) of the nucleus of NGC 4151 obtained with the Gemini Near-infrared Integral Field Spectrograph ( NIFS ) and adaptive optics , to isolate and constrain the properties of a near-IR unresolved nuclear source whose spectral signature is clearly present in our data .
The near-IR spectrum was combined with an optical spectrum obtained with the Space Telescope Imaging Spectrograph which was used to constrain the contribution of a power-law component .
After subtraction of the power-law component , the near-IR continuum is well fitted by a blackbody function , with T = 1285 \pm 50 K , which dominates the nuclear spectrum – within an aperture of radius 0 \farcs 3 – in the near-IR .
We attribute the blackbody component to emission by a dusty structure , with hot dust mass M _ { HD } = ( 6.9 \pm 1.5 ) \times 10 ^ { -4 } { M _ { \odot } } , not resolved by our observations , which provide only an upper limit for its distance from the nucleus of 4 pc .
If the reddening derived for the narrow-line region also applies to the near-IR source , we obtain a temperature T = 1360 \pm 50 K and a mass M _ { HD } = ( 3.1 \pm 0.7 ) \times 10 ^ { -4 } { M _ { \odot } } for the hot dust .
This structure may be the inner wall of the dusty torus postulated by the Unified Model or the inner part of a dusty wind originating in the accretion disk .