The spatial clustering of ROSAT all-sky survey Active Galactic Nuclei: V. The evolution of broad-line AGN clustering properties in the last 6 Gyr

This is the fifth paper in a series of investigations of the clustering properties of luminous, broad emission line active galactic nuclei (AGN) identified in the ROSAT All-Sky Survey (RASS) and Sloan Digital Sky Survey (SDSS). In this work we measure the cross-correlation function (CCF) between RASS/SDSS DR14 AGN with the SDSS CMASS galaxy sample at 0.44 < z < 0.64. We apply halo occupation distribution (HOD) modeling to the CCF along with the auto-correlation function of the CMASS galaxies. We find that X-ray and optically-selected AGN at 0.44 < z < 0.64 reside in statistically identical halos with a typical dark matter halo mass of Mtyp, AGN DMH ∼ 10^12.7h⁻¹ M_⊙. The acceptable HOD parameter space for these two broad-line AGN samples have only statistically marginal differences caused by small deviations of the CCFs in the 1-halo dominated regime on small scales. In contrast to optically-selected AGN, the X-ray AGN sample may contain a larger population of satellites at MDMH ∼ 10¹³h⁻¹ M_⊙. We compare our measurements in this work with our earlier studies at lower independent red shift ranges, spanning a look-back time of 6 Gyr. The comparison over this wider redshift range of 0.07 < z < 0.64 reveals: (i) no significant difference between the typical DMH masses of X-ray and optically-selected AGN, (ii) weak positive clustering dependencies of Mtyp, AGN DMH with LX and MBH, (iii) no significant dependence of Mtyp, AGN DMH on Eddington ratio, and (iv) the same DMH masses host more massive accreting blackholes at high redshift than at low redshifts.