6 X-ray luminosity and Type-2 QSO candidates

We have redshifts (and luminosities) for 61 objects or $\sim$62% of the sample with X-ray spectral analysis. In Fig. 8, we plot X-ray luminosity in the [0.5-2] (a) and [0.5-10] (b) keV rest-frame bands as a function of the $\log(N_{\rm H}$). Type-1 AGN (objects without soft absorption) cover a range between $1 \times 10^{41}$ erg s^-1 and $9 \times 10^{44}$ erg s^-1 in the [0.5-2] keV band; whereas absorbed Type-2 AGN have luminosities in the range $1 \times 10^{41}$- $2 \times 10^{43}$ erg s^-1. In the total band (Fig. 8b) the effect of absorption is less evident so that the range of luminosity of Type-1 ( $1\times 10^{42}$- $2\times 10^{45}$ erg s^-1) and Type-2 AGN ( $1\times 10^{42}$- $2\times 10^{44}$ erg s^-1) is comparable. We have derived the unabsorbed luminosities for objects with $\log(N_{\rm H}) > 21.5$ and reported them in Fig. 8 as arrows. In the soft band (Fig. 8a), where the effect of absorption is stronger, luminosities increase substantially and the range of intrinsic luminosities of Type-2 AGN fall in the same range as that of Type-1's (see also Gilli et al., in preparation). In Fig. 8b, we have highlighted the region where $L_{\rm X}[0.5{-}10]>10^{44}$ erg s^-1 and $\log(N_{\rm H})>22$ cm^-2, i.e. the "Type-2 QSO region''. Six objects fall inside this area: one is optically classified as a Type-1 AGN (see Sect. 7.4 for more details), two are Type-2 AGN. For the remaining three, we derived photometric redshifts and due to their X-ray absorption and optical/near-IR colours are likely Type-2 AGN. Four of them are also EROs. We argue that these six sources are reliable Type-2 QSO candidates. All of them are within an off-axis angle of 10 $\hbox {$^\prime $ }$where the sample is complete (see Sect. 3.3) and we thus derive a density of $\sim$69 objects of this class per square degree.

In Fig. 9, we show the X-ray luminosity as a function of redshift, using the observed hard band luminosity which is relatively unaffected by absorption.