Physical properties of emitting plasma near massive black holes: the Broad Line Region

The dominant emission in Active Galactic Nuclei (AGN) spectra comes from the Broad Emission Lines (BEL) which originate in the Broad Line Region (BLR). The BLR can potentially provide a useful probe of the central part of an AGN, and consequently of the characteristics of the massive Black Hole (BH) that is assumed to be in the center of these objects. The understanding of the physics and kinematics of the BLR is crucial because of the following three reasons: (i) kinematics of the BLR is probably determined by the massive BH, with the competing effects of gravity and radiation pressure, (ii) the BLR reprocesses the UV energy emitted by the continuum source, consequently BEL can provide indirect information about the continuum source, (iii) there is indication that the physical and kinematical parameters of the BEL can be connected with the general characteristics of an AGN (e.g. mass of the BH). In order to connect the physical and kinematical parameters of the BLR, in this work we consider the intensities and widths of Balmer lines of a sample of 90 AGN from Sloan Digital Sky Survey (SDSS). Additionally, we consider the variation of the intensities and widths of Balmer lines from the BLR of NGC 5548 observed from 1996 till 2004. We apply the Boltzmann-Plot method (Popovic 2003, Popovic et al. 2006) to the Balmer line intensities and estimated the electron temperature of a typical BLR. Moreover, we discuss the possibility that the BLR is in general composed from two emitting regions: one that is closer to the BH and contributes to the BEL's wings, and another that is further from the central BH and contributes to the BEL's core.