Astronomy and Astrophysics – Astronomy
Scientific paper
Mar 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...495..196a&link_type=abstract
Astrophysical Journal v.495, p.196
Astronomy and Astrophysics
Astronomy
46
Galaxies: Active, Galaxies: Nuclei, Galaxies: Photometry, Galaxies: Seyfert, Galaxies: Stellar Content, Infrared: Galaxies
Scientific paper
We present a near-infrared J-, H-, K-, and L'-band (1.25-3.80 mu m) imaging study of a sample of Seyfert galaxies, including some of the best studied examples of those with extended emission-line regions (EELRs). The observed near-IR nuclear colors are consistent with a mixture of emissions from an old stellar population and unreddened hot dust. However, if the hot dust is located in the inner part of the dusty torus invoked in unified schemes, the dust emission should suffer substantial reddening. We show that the near-IR nuclear colors may also be reproduced with a combination of emission from unreddened starlight and hot (T = 1200 K) dust reddened by AV ~ 5-30 mag. All of the galaxies exhibit an unresolved nuclear source at L'. The circumnuclear colors (in a 0.5-1.0 kpc annulus) are similar to those of normal spiral galaxies in most cases, although some galaxies exhibit extended emission at L', presumably from hot dust, which causes the circumnuclear K - L' colors to be redder than for normal galaxies. We argue that the circumnuclear hot dust in NGC 1068 and NGC 4151 is probably heated by young stars. A detailed study of the morphologies of the central and circumnuclear regions of the galaxies in our sample is presented. We have constructed smooth models of the old stellar population by fitting elliptical isophotes to the J- and K-band images. The model-divided images are examined for the presence of isophotal deviations from elliptical symmetry, such as internal bars, spiral arms, etc., and compared with the structures seen in optical emission-line images, to study the relative orientations of bars, the EELRs, the nuclear radio emission, and the host galaxy. We find stellar bars in NGC 1068 and NGC 4253 whose orientations are consistent with those of their EELRs and evidence for double bars (or "bars within bars") in Mrk 573, NGC 3081, and NGC 3393. Only in NGC 2110 and NGC 4151 do we find no significant isophotal deviations from elliptical symmetry. Finally, there is an alignment on small scales between the near-IR continuum and the line emission in four galaxies, NGC 1068, NGC 2110, NGC 3081, and NGC 4253. These results seem to suggest that there is not a unique explanation for the orientation of the EELRs seen in Seyfert galaxies. In some cases, the EELRs could represent gas aligned with the nuclear stellar bars, whereas in others, they are more likely to be related to gas escaping along the minor axis of the galaxies.
Alonso-Herrero Almudena
Simpson Chris
Ward Martin J.
Wilson Andrew S.
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