NASA Logo, External Link
Facebook icon, External Link to NASA STI page on Facebook Twitter icon, External Link to NASA STI on Twitter YouTube icon, External Link to NASA STI Channel on YouTube RSS icon, External Link to New NASA STI RSS Feed AddThis share icon
 

Record Details

Record 7 of 7
Optically thin broad-line clouds in active galactic nuclei
External Online Source: doi:10.1086/175378
Author and Affiliation:
Shields, Joseph C.(Univ. of Arizona, Tucson, AZ, United States)
Ferland, Gary J.(Univ. of Kentucky, Lexington, KY, United States)
Peterson, Bradley M.(Ohio State Univ., Columbus, OH, United States)
Abstract: The broad-line region (BLR) in Seyfert galaxy nuclei exhibits correlated variations in continuum and emission-line luminosity that are qualitatively consistent with photoionization of ionization-bounded (optically thick) clouds. However, evidence is growing that a nonnegligible fraction of the BLR cloud population is optically thin to the Lyman continuum and fully ionized in hydrogen. We consider the implications of this nebular component for observed line emission and find that inclusion of thin clouds in photoionization calculations can resolve several outstanding puzzles of Seyfert variability, notably the behavior of the C IV lambda 1549/Ly-alpha ratio as a function of continuum luminosity. A similar population of thin clouds located along our line of sight can account for observed ultraviolet absorption features and 'warm absorber' behavior at X-ray energies. The Baldwin effect for active galaxies, a negative correlation between ultraviolet emission-line equivalent width and continuum luminosity, can also be explained in detail by a decrease in the covering factor of an optically thin component with increasing source luminosity. The luminosity dependence of covering factor may result from outflows of thin clouds that proceed more efficiently in intrinsically brighter sources. The presence of absorption features in active galactic nuclei (AGNs) that are blueshifted and attain the highest velocities in broad absorption line features associated with luminous QSOs would be consistent with this interpretation.
Publication Date: Mar 10, 1995
Document ID:
19950049052
(Acquired Dec 28, 1995)
Accession Number: 95A80651
Subject Category: ASTROPHYSICS
Document Type: Journal Article
Publication Information: Astrophysical Journal, Part 1 (ISSN 0004-637X); 441; 2; p. 507-520
Publisher Information: United States
Contract/Grant/Task Num: NAS5-26555; HF-1052.01-93-A; NAGW-3315
Financial Sponsor: NASA; United States
Organization Source: NASA; Washington, DC, United States
NASA Goddard Space Flight Center; Greenbelt, MD, United States
Description: 14p; In English
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: Copyright
NASA Terms: ACTIVE GALACTIC NUCLEI; CONTINUOUS SPECTRA; EMISSION SPECTRA; INTERSTELLAR GAS; LINE SPECTRA; SEYFERT GALAXIES; STELLAR LUMINOSITY; VARIABILITY; ABSORPTIVITY; CARBON; LYMAN SPECTRA; OPTICAL THICKNESS; PHOTOIONIZATION; ULTRAVIOLET SPECTRA; X RAY SPECTRA
Imprint And Other Notes: Astrophysical Journal, Part 1 vol. 441, no. 2 p. 507-520 March 10, 1995
Availability Source: Other Sources
› Back to Top
Find Similar Records
NASA Logo, External Link
NASA Official: Gerald Steeman
Site Curator: STI Program
Last Modified: August 19, 2011
Contact Us