An XMM-Newton spectral survey of 12 micron selected galaxies. II.
  Implications for AGN selection and unification
  We present a multi-waveband analysis of a 126 galaxy sub-sample of the 12
micron galaxy sample (12MGS), for which we have carried out a detailed X-ray
spectral analysis of in a previous paper. We present optical activity classes
and we characterise these by their X-ray, 12 um and [OIII] luminosities and by
their X-ray spectral properties. Our most interesting results are: Seyfert (Sy)
1s and Sy 2s show significantly different LX distributions from each other; Sy
2s with a detection of an HBLR show a significantly higher LX than those
without a detection; Sy 1s also present a significantly different L(12um)
distribution from both Sy1.2-1.9s and Sy 2s; the Sy 2 fraction decreases
towards high LX; X-ray indications of AGN power agree well with the optical
classifications; There is X-ray evidence for the presence of an AGN in 17% of
HII/AGN composites and 40% of LINERs; we advocate the use of a LX >10^41 erg/s
in the X-ray selection of AGN, which gives a contamination rate of only 3% from
star-forming galaxies; Sy 1s and Sy 2 have the same intrinsic {\Gamma}; in 24%
of cases the absorption measured in X-rays does not correspond directly with
that implied in the optical band from the visibility of the BLRs; the obscured
fraction in AGN is a strong function of LX peaking at 10^42 erg/s; The average
obscured and Compton thick fractions for this sample are 62\pm5% and 20\pm4%
respectively, which are higher than hard X-ray and optically selected samples;
we assess the use of the T ratio (FX/F[OIII]) for selecting Compton thick
candidates. We conclude here that this quantity can often be unreliable due
uncertainties in the extinction corrections to the [OIII] flux. These results
have important impacts on AGN selection and unification and the results from
the 12MGS are particularly useful as a local analogue to z=1 24 um samples.
