Optical and X-ray properties of the RIXOS AGN — II. Emission lines

We present the optical and UV emission line properties of 160 X-ray selected AGN taken from the RIXOS survey (including H�, H�, [Oiii]�5007, Mgii�2798 and Ciii]�1909). This sample is believed to contain a mixture of absorbed and unabsorbed objects, with column densities up to � 4 × 10 21 cm 2 . Although the distribution of the [Oiii]�5007 EW for the RIXOS AGN is typical of optically-selected samples, the Balmer line EWs are relatively low. This is consistent with the presence of a dust absorber between the broad and narrow line regions (e.g. a molecular torus), and intrinsically weak optical line emission. We find Baldwin effects in Ciii]�1909 and Mgii�2798, and a positive response of the Mgii line to its ionizing continuum. There is a strong correlation between the EW and FWHM of Mgii, which may be similar to that seen in other samples for H�. We demonstrate that this is consistent with models which suggest two line-emitting zones, a ‘very broad line region’ (VBLR) and an ‘intermediate line region’ (ILR). The correlation between EW and FWHM in Mgii may be a physical characteristic of the ILR: e.g. the radiative acceleration of the line-emitting clouds; or it may reflect a geometric dependence, e.g. anisotropies in the line or continuum emission, or a smaller covering factor of the ILR at large distances.