Astronomy and Astrophysics – Astrophysics
Scientific paper
2002-02-13
Astronomy and Astrophysics
Astrophysics
26 pages, 5 figures. Accepted for publication in ApJ
Scientific paper
10.1086/340192
UV, visible, and near-infrared spectroscopy is used to study the transitions of neutral oxygen leading to the emission of broad OI $\lambda$8446, $\lambda$11287 and $\lambda$1304 in Active Galactic Nuclei. From the strength of the former two lines, contrary to the general belief, we found that in six out of seven galaxies, L-beta fluorescence is not the only mechanism responsible for the formation of these three lines. Because OI $\lambda$13165 is almost reduced to noise level, continuum fluorescence is ruled out as an additional excitation mechanism, but the presence of OI $\lambda$7774 in one of the objects suggests that collisional ionization may have an important role in the formation of OI $\lambda$8446. The usefulness of the OI lines as a reliable reddening indicator for the broad line region is discussed. The values of E(B-V) derived from the OI $\lambda 1304/\lambda$8446 ratio agree with those obtained using other reddening indicators. The observations point toward a break in the one-to-one photon relation between OI $\lambda$8446 and OI $\lambda$1304, attributable to several destruction mechanisms that may affect the latter line.
Donzelli Carlos José
Pastoriza Miriani Griselda
Prato Lisa
Rodriguez-Ardila Alberto
Viegas M. M. S.
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