Bias factor (a) and mass of AGN hosting halos (b) as a function of redshift for X-ray-selected AGN (black data points), X-ray-selected Type 1 AGN (blue data points), and X-ray selected Type 2 AGN (red data points) as estimated in different surveys (COSMOS, Gilli et al. [44], Allevato et al. [45]; CDFN, Gilli et al. [33], Yang et al. [34]; Swift-BAT, Cappelluti et al. [51]; CDFS, Gilli et al. [33]; AEGIS, Coil et al. [48]; AGES, Hickox et al. [47]; ROSAT-NEP, Mullis et al. [24]; ROSAT-SDSS, Krumpe et al. [50]; CLASXS, Yang et al. [34]). The dashed lines show the expected of DMHs with different masses according to the legend, based on Sheth et al.[55]. The grey points show results from quasar-quasar correlation measurements using spectroscopic samples from SDSS [59, 60], 2QZ [61, 62], and 2SLAQ [63]. All the previous studies infer the picture that X-ray-selected AGN which are moderate luminosity AGN compared to bright quasars inhabit more massive DMHs than optically selected quasars in the range .
