Warm IRAS Sources from the Point Source Catalog - Part Three - Emission Line Properties Correlations and AGN / Active Galactic Nuclei / Unified Models

Details Warm IRAS Sources from the Point Source Catalog - Part Three - Emission Line Properties Correlations and AGN / Active Galactic Nuclei / Unified Models Warm IRAS Sources from the Point Source Catalog - Part Three - Emission Line Properties Correlations and AGN / Active Galactic Nuclei / Unified Models

Mar 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...283..791k&link_type=abstract

Astronomy and Astrophysics, Vol. 283, NO. 3/MAR(III), P. 791, 1994

Astronomy and Astrophysics

Astrophysics

44

Scientific paper

We consider correlations between emission-line properties and infrared parameters for 221 emission-line AGN associated with "warm" sources from the IRAS Point Source Catalog. Our analysis includes properties directly associated with the IR-emitting dust component as well as tests of geometric orientation schemes for unifying broad- and narrow-line AGN. The narrow-line reddening (from Hα/Hβ) and ionization level (from (O III]/Hβ and [N II]/Hα) are both correlated with the parameters characterizing the mid-IR emission. This is consistent with a model in which the mid-IR emission is produced partially by dust located within the narrow-line region, perhaps within the emission-line filaments themselves. Since this sample is selected using a (nominally) isotropic property, we may examine the popular hypothesis that broad-line and narrow-line objects differ primarily in their observed orientation. The relative- [O III] and IR luminosities of these two classes show very similar distributions, strengthening the case for a unified classification. However, Fe II emission depends as much on far-IR spectral shape as on relative IR loudness, in contrast to earlier claims from small numbers of anomalous AGNs from the IRAS survey. This may be accommodated under geometrically unified schemes only if the scale of the Fe II region is of the same order as that of structure in the warmest dust zone and if its geometry differs from that of the region emitting, for example, broad Balmer lines. Line-width similarities make this difficult to accommodate in a simple picture, suggesting that Fe II emission is linked to some intrinsic property of certain AGN. The small number of very luminous narrow-line objects ("QSO 2") has suggested a luminosity dependence of the covering fraction of the obscuring material. We examine this by comparing the emission-line and IR luminosities of these AGN. As shown by this ratio, the covering factor of dust shows large scatter with the mean actually increasing toward higher luminosities. There is substantial overlap between broad- and narrow-line objects at all luminosities, with some Seyfert 2 galaxies having larger dust covering than any broad-line objects. This scatter overwhelms any overall trends that could account for the paucity of luminous narrow-line objects.

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