Sub-arcsec mid-IR observations of NGC 1614: Nuclear star-formation or an
  intrinsically X-ray weak AGN?
  We present new mid-infrared N-band spectroscopy and Q-band photometry of the
local luminous infrared galaxy NGC1614, one of the most extreme nearby
starbursts. We analyze the mid-IR properties of the nucleus (central 150 pc)
and four regions of the bright circumnuclear (diameter~600 pc) star-forming
(SF) ring of this object. The nucleus differs from the circumnuclear SF ring by
having a strong 8-12 micron continuum (low 11.3 micron PAH equivalent width).
These characteristics, together with the nuclear X-ray and sub-mm properties,
can be explained by an X-ray weak active galactic nucleus (AGN), or by peculiar
SF with a short molecular gas depletion time and producing an enhanced
radiation field density. In either case, the nuclear luminosity (L(IR) < 6e43
erg/s) is only <5% of the total bolometric luminosity of NGC1614. So this
possible AGN does not dominate the energy output in this object. We also
compare three star-formation rate (SFR) tracers (Pa$\alpha$, 11.3 micron PAH,
and 24 micron emissions) at 150 pc scales in the circumnuclear ring. In
general, we find that the SFR is underestimated (overestimated) by a factor of
2-4 (2-3) using the 11.3 micron PAH (24 micron) emission with respect to the
extinction corrected Pa$\alpha$ SFR. The former can be explained because we do
not include diffuse PAH emission in our measurements, while the latter might
indicate that the dust temperature is particularly warmer in the central
regions of NGC1614.
