The subarcsecond mid-infrared view of local active galactic nuclei: II.
  The mid-infrared--X-ray correlation
  We present an updated mid-infrared (MIR) versus X-ray correlation for the
local active galactic nuclei (AGN) population based on the high angular
resolution 12 and 18um continuum fluxes from the AGN subarcsecond MIR atlas and
2-10 keV and 14-195 keV data collected from the literature. We isolate a sample
of 152 objects with reliable AGN nature and multi-epoch X-ray data and minimal
MIR contribution from star formation. Although the sample is not homogeneous or
complete, we show that our results are unlikely to be affected by biases. The
MIR--X-ray correlation is nearly linear and within a factor of two independent
of the AGN type and the wavebands used. The observed scatter is <0.4 dex. A
possible flattening of the correlation slope at the highest luminosities probed
(~ 10^45 erg/s) is indicated but not significant. Unobscured objects have, on
average, an MIR--X-ray ratio that is only <= 0.15 dex higher than that of
obscured objects. Objects with intermediate X-ray column densities (22 < log
N_H < 23) actually show the highest MIR--X-ray ratio on average. Radio-loud
objects show a higher mean MIR--X-ray ratio at low luminosities, while the
ratio is lower than average at high luminosities. This may be explained by
synchrotron emission from the jet contributing to the MIR at low-luminosities
and additional X-ray emission at high luminosities. True Seyfert 2 candidates
and double AGN do not show any deviation from the general behaviour. Finally,
we show that the MIR--X-ray correlation can be used to verify the AGN nature of
uncertain objects. Specifically, we give equations that allow to determine the
intrinsic 2-10 keV luminosities and column densities for objects with complex
X-ray properties to within 0.34 dex. These techniques are applied to the
uncertain objects of the remaining AGN MIR atlas, demonstrating the usefulness
of the MIR--X-ray correlation as an empirical tool.
