Implications of CA II emission for physical conditions in the broad-line region of active galactic nuclei

Abstract

view Abstract Citations (149) References (88) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Implications of CA II Emission for Physical Conditions in the Broad-Line Region of Active Galactic Nuclei Ferland, Gary J. ; Persson, S. Eric Abstract This paper summarizes observations of Ca II emission from active galactic nuclei (AGNs) and discusses their implications for conditions in the emitting gas. Observations of Ca II K and H, the infrared triplet, and the forbidden lines near 7300 A are compiled to give a "standard" set of line ratios for AGNs with relatively strong Fe II emission. A series of photoionization calculations is presented which examines the conditions needed to produce the observed emission. We pay special attention to the inclusion of heating due to free-free and H^-^ absorption, processes which couple the near-infrared to millimeter continuum with the emitting gas. These are often the main agents heating the clouds at large column densities. A mean continuum, deduced by Mathews and Ferland and extending from 1 mm to 100 MeV, with a "blue bump" peaking at roughly 60 eV, is used. Regardless of density or ionization parameters, thin clouds (with column densities ~ 10^23^ cm^-2^) cannot produce the observed Ca II emission. The calculations show that the C III] λ1909/C IV λ1549 intensity ratio is not a good indicator of the ionization parameter for this continuum; for large ionization parameters carbon and oxygen Stromgren spheres form, and the C III]/C IV line ratio is double-valued. Clouds with large column densities and ionization parameters, which use an ionizing flux deduced from line reverberation studies, largely reproduce the observed carbon, calcium, and hydrogen spectrum. These calculations suggest a very different picture of BLR clouds than some previous studies. Very large column densities are required to reproduce the Ca II spectrum; indeed, the calculations show that the observed line spectrum imposes no limit on how large this might be, just as the carbon spectrum imposes no limit on the ionization parameter. An important result is that cloud pressure is entirely dominated by radiation pressure. This suggests that the clouds are not stable, while the large column density suggests that the clouds might be a wind or corona above a star or accretion disk. Publication: The Astrophysical Journal Pub Date: December 1989 DOI: 10.1086/168156 Bibcode: 1989ApJ...347..656F Keywords: Active Galactic Nuclei; Calcium; Emission Spectra; Photoionization; Spectral Line Width; Continuous Spectra; Fine Structure; Forbidden Transitions; H Lines; K Lines; Molecular Clouds; Seyfert Galaxies; Astrophysics; CA II EMISSION; GALAXIES: NUCLEI; GALAXIES: SEYFERT; QUASARS full text sources ADS | data products SIMBAD (13) NED (13)