Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...443..617s&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 443, no. 2, p. 617-624
Astronomy and Astrophysics
Astronomy
75
Active Galactic Nuclei, Astronomical Models, Balmer Series, H Alpha Line, H Beta Line, Line Shape, Seyfert Galaxies, Variability, Accretion Disks, Astronomical Observatories, Astronomical Spectroscopy, Black Holes (Astronomy), Flux (Rate), Gas Flow, Interstellar Extinction, Ionization
Scientific paper
We present spectroscopic observations of the nucleus of the Seyfert/low-ionization nuclear emission-line region galaxy NGC 1097 spanning the period 1991-1994. The goal was to monitor anticipated variations of the broad, double-peaked Balmer lines which appeared abruptly in 1991. We find that the broad Balmer lines have varied significantly over the monitoring period, both in their integrated fluxes and in their profile shapes. The integrated H-alpha flux has decreased by a factor of 2, the (H-alpha)/(H-beta) ratio has increased, and the originally asymmetric H-alpha profile has become symmetric. The decline of the H-alpha flux and the change in the (H-alpha)/(H-beta) ratio can be interpreted as consequences of either increased obscuration along the line of sight, or a decline in the ionizing continuum, but neither of these scenarios can account for the change in profile shapes. A model attributing the line emission to a precessing elliptical ring around a 106 solar mass nuclear black hole can reproduce the observed profile variations. In this scenario, the line-emitting ring is the result of the tidal disruption of a star by the black hole. Alternative scenarios associating the broad-line emission with a collimated bipolar outflow also remain viable, but binary black holes and inhomogeneous accretion disks are disfavored by the observed pattern of variability.
Eracleous Michael
Filippenko Alexei V.
Halpern Jules P.
Livio Mario
Storchi-Bergmann Thaisa
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