Line-Width Correlations in Seyfert Galaxies. Application to MKN 463E and NGC 5548

Details Line-Width Correlations in Seyfert Galaxies. Application to MKN 463E and NGC 5548 Line-Width Correlations in Seyfert Galaxies. Application to MKN 463E and NGC 5548

Dec 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aas...183.4601m&link_type=abstract

American Astronomical Society, 183rd AAS Meeting, #46.01; Bulletin of the American Astronomical Society, Vol. 25, p.1361

Astronomy and Astrophysics

Astronomy

Scientific paper

The well known correlations of emission-line widths (from the NLR of Seyfert galaxies) with the ionization potential and/or critical density of the emitting species have ambiguous interpretation. The emission lines from highly ionized atoms tend to have high critical density. By comparing line-widths of species with similar ionization structure but different critical density, we argue that observed correlations of line-width with ionization potential and/or critical density are best interpreted as correlations with ionization potential alone. We suggest an interpretation of line-width correlations with ionization potential as a column density effect. To emit the lines of low ionization ([S II] lambda lambda 6716,6731, [O II] lambda lambda 3726,3729, and [O I] lambda 6300 in particular), a minimum column density, Nmin, is required. Lines of high ionization (e.g. [Fe VII] lambda 6087) are emitted for any column density provided the ionization parameter is sufficient. Therefore, if the ratio, {Ncol / Nmin}, where Ncol is the cloud column density, increases in the direction of decreasing velocity, correlations similar to those observed would be expected. Spherical clouds of constant mass and constant ionization parameter have {Ncol / Nmin} increasing inward so that observed line-width correlations can be reconciled with cloud velocity decreasing inward. One well known object which is particularly relevant to the above discussion is Mkn 463E. We present line profiles of Mkn 463E with blue wings extending out to 2,000 km s(-1) in the lines of lowest critical density. Combined with the presence of strong [O III] lambda 4363 emission, which requires the presence of high density gas somewhere in the NLR, the presence of extended wings argues strongly for velocity increasing outward in this object. We also point out that NGC 5548 is anomalous in that the line widths appear to correlate with critical density rather than ionization potential. This work has been supported by NASA grant NAG 5-1630.

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