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Optically thin thermal emission as the origin of the big bump in the spectra of active galactic nuclei

1990; IOP Publishing; Volume: 363; Linguagem: Inglês

10.1086/185856

1538-4357

G. J. Ferland, K. T. Korista, B. M. Peterson,

Astrophysical Phenomena and Observations

view Abstract Citations (102) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optically Thin Thermal Emission as the Origin of the Big Bump in the Spectra of Active Galactic Nuclei Ferland, G. J. ; Korista, K. T. ; Peterson, B. M. Abstract The nature of the "big bump," the excess of ultraviolet emission seen in many active nuclei, is a clue to the source of the energy generation in the central regions of quasars. We report observations of the Seyfert galaxy Mrk 590, which show dramatic changes in both the continuum and hydrogen lines, thus offering a clue to the origin of the "big bump." While the continuum luminosity increased by ~ 0.5 dex, the core of the Balmer lines increased by a similar amount, but the broad wings of the hydrogen lines maintained constant luminosity. If hydrogen lines are produced by photoinization, nebular theory then suggests that the core of the line arises in matter which is optically thick to the ionizing continuum, while the line wings (presumably formed nearer the central object) arise in matter which is optically thin in this continuum and which nearly fully covers the continuum source. Using the "very broad line region" (VBLR) line luminosity to establish the emission measure, we then show that emission from VBLR gas can fully account for the ultraviolet continuum if it has a temperature of ~ 10^5^ K., The VBLR is the likely site for the soft X- ray "warm absorbing" material as well as the radio free-free emission. If the VBLR gas lies between the source of the power-law continuum and the broad line region, then photoelectric absorption of hard radiation (hv >= 50 eV) by the VBLR can produce the type of soft radiation field inferred to strike the BLR by recent studies of Fairall 9. This result in a unified picture, in which the central source of power-law radiation is surrounded by ionized partially transparent gas (the VBLR) which reprocesses ~ 100 eV photons into the "big bump." This in turn is surrounded by on outer, more neutral, BLR, which produces the sharp cores of the emission lines. Publication: The Astrophysical Journal Pub Date: November 1990 DOI: 10.1086/185856 Bibcode: 1990ApJ...363L..21F Keywords: Active Galactic Nuclei; Markarian Galaxies; Optical Thickness; Seyfert Galaxies; Thermal Emission; Astronomical Spectroscopy; Balmer Series; Line Spectra; Ultraviolet Radiation; X Ray Spectra; Astrophysics; GALAXIES: INDIVIDUAL NAME: MARKARIAN 590; GALAXIES: SEYFERT; LINE PROFILES; RADIATION MECHANISMS; X-RAYS: GENERAL full text sources ADS | data products SIMBAD (3) NED (1)