[O III]$\hat{I}»5007$ and X-ray Properties of a Complete Sample of Hard X-ray Selected AGNs in the Local Universe

Abstract

We study the correlation between the [O III]$\hat{I}»5007$ and X-ray luminosities of local Active Galactic Nuclei (AGNs), using a complete, hard X-ray ($>10$ keV) selected sample in the Swift/BAT 9-month catalog. From our optical spectroscopic observations at the South African Astronomical Observatory and the literature, a catalog of [O III]$\hat{I}»5007$ line flux for all 103 AGNs at Galactic latitudes of $|b|>15^{\circ }$ is complied. Significant correlations with intrinsic X-ray luminosity ($L_{\mathrm{X}}$) are found both for observed ($L_{[\mathrm{O}\mathrm{III}]}$) and extinction-corrected ($L_{[\mathrm{O}\mathrm{III}]}^{\mathrm{cor}}$) luminosities, separately for X-ray unabsorbed and absorbed AGNs. We obtain the regression form of $L_{[\mathrm{O}\mathrm{III}]}$ $\propto L_{2-10\mathrm{keV}}^{1.18\pm 0.07}$ and $L_{[\mathrm{O}\mathrm{III}]}^{\mathrm{cor}}$ $\propto L_{2-10\mathrm{keV}}^{1.16\pm 0.09}$ from the whole sample. The absorbed AGNs with low ($<$0.5\%) scattering fractions in soft X-rays show on average smaller $L_{[\mathrm{O}\mathrm{III}]}/L_{\mathrm{X}}$ and $L_{[\mathrm{O}\mathrm{III}]}^{\mathrm{cor}}/L_{\mathrm{X}}$ ratios than the other absorbed AGNs, while those in edge-on host galaxies do not. These results suggest that a significant fraction of this population are buried in tori with small opening angles. By using these $L_{[\mathrm{O}\mathrm{III}]}$ vs. $L_{\mathrm{X}}$ correlations, the X-ray luminosity function of local AGNs (including Compton thick AGNs) in a standard population synthesis model gives much better agreement with the [O III]$\hat{I}»5007$ luminosity function derived from the Sloan Digital Sky Survey than previously reported. This confirms that hard X-ray observations are a very powerful tool to find AGNs with high completeness.

14 pages including 11 figures and 3 tables, accepted for publication in ApJ. In this manuscript, the observed 14-195 keV luminosities in Table 1 have been corrected to be exactly the same as in the original Swift/BAT 9-month catalog. Accordingly, Figures 2(a) and 3(a) and a part of Tables 2 and 3 have been updated. The changes from the previous version are small and do not affect the text