After recent sensitivity upgrades at the Keck Interferometer ( KI ) , systematic interferometric 2 \mu m studies of the innermost dust in nearby Seyfert nuclei are within observational reach .
Here , we present the analysis of new interferometric data of NGC 4151 , discussed in context of the results from recent dust reverberation , spectro-photometric and interferometric campaigns .
The complete data set gives a complex picture , in particular the measured visibilities from now three different nights appear to be rather insensitive to the variation of the nuclear luminosity .
KI data alone indicate two scenarios : the K -band emission is either dominated to \sim 90 \% by size scales smaller than 30 mpc , which falls short of any dust reverberation measurement in NGC 4151 and of theoretical models of circum-nuclear dust distributions .
Or contrary , and more likely , the K -band continuum emission is dominated by hot dust ( \gtrsim 1300 ~ { } K ) at linear scales of about 50 mpc .
The linear size estimate varies by a few tens of percent depending on the exact morphology observed .
Our interferometric , deprojected centro-nuclear dust radius estimate of 55 \pm 5 mpc is roughly consistent with the earlier published expectations from circum-nuclear , dusty radiative transfer models , and spectro-photometric modeling .
However , our data do not support the notion that the dust emission size scale follows the nuclear variability of NGC 4151 as a R _ { dust } \propto L _ { nuc } ^ { 0.5 } scaling relation .
Instead variable nuclear activity , lagging , and variable dust response to illumination changes need to be combined to explain the observations .