  In order to examine the relative importance of powerful starbursts and
Compton-thick AGNs in NGC 6240, we have obtained mid-infrared images and
low-resolution spectra of the galaxy with sub-arcsecond spatial resolution
using the Keck Telescopes. Despite the high spatial resolution (~200 pc) of our
data, no signature of the hidden AGNs has been detected in the mid-infrared.
The southern nucleus, which we show provides 80-90% of the total 8-25 um
luminosity of the system, has a mid-infrared spectrum and a mid-/far-infrared
spectral energy distribution consistent with starbursts. At the same time,
however, it is also possible to attribute up to 60% of the bolometric
luminosity to an AGN, consistent with X-ray observations, if the AGN is heavily
obscured and emits mostly in the far-infrared. This ambiguity arises because
the intrinsic variation of properties among a given galaxy population (e.g.,
starbursts) introduces at least a factor of a few uncertainty even into the
most robust AGN-starburst diagnostics. We conclude that with present
observations it is not possible to determine the dominant power source in
galaxies when AGN and starburst luminosities are within a factor of a few of
each other.
