Astronomy and Astrophysics – Astrophysics
Scientific paper
1992-10-20
Astronomy and Astrophysics
Astrophysics
15 pages + 1 Table and 3 Figures (not included but available upon request), LaTex
Scientific paper
10.1086/172692
We present a high S/N spectrum for the quasar PG 1138+222. We detect a very broad HeII$\lambda$4686 emission line component with twice the FWHM of the conventional broad line region (BLR) as evidenced by the Balmer lines. The profile shape and centroid redshift also distinguish this HeII component from the BLR features. The large ratio of HeII\l 4686 to any analogous H$\beta$ emission component is an indicator that it arises in a very high density region ($n_e \simgt 10^{11}-10^{13}$ \cm3). This Helium component is probably emitted in a Very Broad Line Region (VBLR), where the radiation field is so strong that the Str\"omgren depth becomes similar to the geometrical thickness of the emitting clouds. The gas could therefore be optically thin to the Lyman continuum.
Marziani Paolo
Sulentic Jack W.
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