Kinematics and Ionization of Extended Gas in Active Galaxies. VI. The Seyfert 2 Galaxy NGC 1386
Abstract
We present the results of direct imaging with a CCD detector and long-slit medium- and low-dispersion spectroscopy of the spatially extended narrow line-emitting gas in the highly inclined nearby Seyfert 2 galaxy NGC 1386. The images and spectra have been used to investigate the distribution, kinematics, and ionization structure of the excited gas in the regions surrounding the nucleus out to a distance of approximately 1.0 kpc. An elongated high-excitation nebulosity extends 6" (~ 500 pc) N and S of the nucleus, where it ends abruptly. Further out, emission lines from H II regions in spiral arms are seen. Within the high-excitation region, line widths of up to 1500 km s^-1^ are found, and the sense of line asymmetry switches across the nucleus. The velocity field is interpreted in terms of a combination of a normally rotating component (which dominates the line peaks) and a component undergoing high-velocity infall or outflow (which is responsible for the wings). The optical nucleus is displaced by 1"-1.5" (80-120 pc) from the kinematic center of the rotation curve. The nature of this displacement is briefly discussed. Line ratio diagnostics show that the spectrum at the nucleus is typical of Seyfert 2 nuclei. The ratio [O III] {λ5007/Hβ_corr_ remains high (more than about 10) over the high-excitation nebulosity. However, the ratio [N II] λ6583/Hα_corr_ increases toward the NE and SW edges of the nebulosity, where values as high as 2.9 are found, and where the spectrum is LINER-like. We suggest that this increase in [N II] λ6583/Hα_corr_ may reflect either: (1) photoionization with a decrease in the ionization parameter with increasing distance from the nucleus, along with a general overabundance of nitrogen; or (2) photoionization plus effects of shock heating near the edges of the high-excitation nebulosity, where the ratios are the highest. These edges, where the width of [N II] λ6583 is >= 200 km s^- 1^, may be transition zones resulting from shock fronts at the interface between the outflowing Seyfert-excited gas and ambient gas in the galaxy disk.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 1991
- DOI:
- 10.1086/169539
- Bibcode:
- 1991ApJ...366...50W
- Keywords:
-
- Active Galactic Nuclei;
- Astronomical Spectroscopy;
- Interstellar Gas;
- Ionized Gases;
- Seyfert Galaxies;
- Charge Coupled Devices;
- Emission Spectra;
- Galactic Nuclei;
- H Ii Regions;
- Kinematics;
- Photoionization;
- Shock Fronts;
- Astrophysics;
- GALAXIES: INDIVIDUAL NGC NUMBER: NGC 1386;
- GALAXIES: INTERNAL MOTIONS;
- GALAXIES: NUCLEI;
- GALAXIES: SEYFERT