Insights Into AGN and Host Galaxy Co-evolution From Hard X-ray Emission
  We study the AGN-host co-evolution issue here by focusing on the correlation
between the hard X-ray emission from central AGNs and the stellar populations
of the host galaxies. By focusing on the galaxies with strong H$\alpha$ line
emission (EW(H$\alpha)>5$\AA), both X-ray and optical spectral analysis are
performed on 67 (partially) obscured AGNs that are selected from the \it
XMM-Newton\rm\ 2XMMi/SDSS-DR7 catalog originally cross-matched by Pineau et al.
The sample allows us to study central AGN activity and host galaxy directly and
simultaneously in individual objects. Combining the spectral analysis in both
bands reveals that the older the stellar population of the host galaxy, the
harder the X-ray emission will be, which was missed in our previous study where
the \it ROSAT\rm\ hardness ratios are used. By excluding the contamination from
the host galaxies and from the jet beaming emission, the correlation indicates
that the Compton cooling in the accretion disk corona decreases with the mean
age of the stellar population. We argue that the correlation is related to the
correlation of $L/L_{\mathrm{Edd}}$ with the host stellar population. In
addition, the [\ion{O}{1}]/H$\alpha$ and [\ion{S}{2}]/H$\alpha$ narrow-line
ratios are identified to correlate with the spectral slope in hard X-ray, which
can be inferred from the currently proposed evolution of the X-ray emission
because of the confirmed tight correlations between the two line ratios and
stellar population age.
