The analysis of the broad hydrogen Balmer line ratios: Possible implications for the physical properties of the broad line region of AGNs

Aims: We analyze the ratios of the broad hydrogen Balmer emission lines (from H\u3b1 to H\u25b) in the context of estimating the physical conditions in the broad line region (BLR) of active galactic nuclei (AGNs). Methods: Our measurements of the ratios of the Balmer emission lines are obtained in three ways: i) using photoionization models obtained with a spectral synthesis code CLOUDY; ii) applying the recombination theory for hydrogenic ions; iii) measuring the lines in observed spectra taken from the Sloan Digital Sky Survey database. We investigate the Balmer line ratios in the framework of the so-called Boltzmann plot (BP), analyzing the physical conditions of the emitting plasma for which we could use the BP method. The BP considers the ratio of Balmer lines normalized to the atomic data of the corresponding line transition, and in that way differs from the Balmer decrement. Results: We find that for a certain range of thermodynamic parameters, there are objects that follow the BP. These AGNs may have a BLR consisting of mostly high density plasma

Linear Spectropolarimetric Analysis of Fairall 9 with VLT/FORS2

The quasar main sequence appears to be an incredibly powerful tool to organize the diversity in large samples of type-1 quasars but the most important physical parameters governing it are still unclear. Here, we investigate the origin of the broadening and of a defining feature of Population B sources: a strong redward asymmetry of the Balmer emission lines. We focus on a prototypical source, Fairall 9. Spectropolarimetric data of the Fairall 9 broad H β and H α profiles allowed for a view of the geometric and dynamical complexity of the line emitting regions. Measurements (1) provided evidence of rotational motion; (2) were helpful to test the presence of polar and equatorial scatterers, and their association with non-virial motions. However, we suggest that the polarization properties appear to be more consistent with a warped disc geometry induced by Lense–Thirring precession. © 2021 The Author(s).BWJ and JMW acknowledge financial support from the National Natural Science Foundation of China (11833008 and 11991054), from the National Key Research and Development Program of China (2016YFA0400701), from the Key Research Program of Frontier Sciences, Chinese Academy of Sciences (CAS; QYZDJ-SSW-SLH007), and from the CAS Key Research Program (KJZD-EW-M06). VLA and ES thank the grant of Russian Science Foundation project number 20-12-00030 ‘Investigation of geometry and kinematics of ionized gas in active galactic nuclei by polarimetry methods’, which supported the spectropolarimetric data analysis. ĐS and LČP acknowledge funding provided by the Astronomical Observatory Belgrade (the contract 451-03-68/2020-14/200002) through the grants by the Ministry of Education, Science, and Technological Development of the Republic of Serbia. This work was supported by the F.R.S.–FNRS under grant PDR T.0116.21. AdO acknowledges financial support from the Spanish grants MCI PID2019-106027GB-C41 and the State Agency for Research of the Spanish MCIU through the ‘Center of Excellence Severo Ochoa’ award for the IAA (SEV-2017-0709). Under the same award, PM acknowledges the Hypatia of Alexandria visiting grant.Peer reviewe