LINE-PROFILES OF THE 2-PHASE MEDIUM BROAD-LINE REGION IN ACTIVE GALACTIC NUCLEI

In the framework of BLR in AGNs, i.e. large number of small, cold and dense emission-line clouds immerging in an intercloud hot medium a del icate radiation model for a typical emission cloud is established, in which the backside photoionization of the cloud against the central co ntinuum source by the scattered diffuse continuum in the hot medium is considered. Under the assumption of the radial kinematics of the BLR clouds, the line profiles for the two important UV emission-lines, Ly alpha and CIV lambda 1549 are computed; and based on these calculation s, various physical factors that affect the properties of the emission -line profiles are discussed. It is concluded that: (i) when the BLR c louds is inflow, there exists a confining hot medium with density arou nd 2x10(5) cm(-3). In this case, theoretical line profiles agree well with the observational; (ii) both symmetric Ly alpha and nearly symmet ric CIV line profiles show blue velocity shifts, the quantities of whi ch are sensitive to the cutoff of the outer radius of the BLR. It is s uggested that this cutoff effect is physical background to explain the observations that high ionization lines in the spectra of AGNs have s ome systematic blue shifts relative to those low ionization lines whic h usually characterize their source system velocities.