Other
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...437..149a&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 437, no. 1, p. 149-161
Other
22
Active Galactic Nuclei, Astronomical Models, Gas Dynamics, Gas Ionization, H Ii Regions, Interstellar Gas, Kinematics, Seyfert Galaxies, Astronomical Spectroscopy, Continuums, Mathematical Models
Scientific paper
We present bidimensional spectroscopy of the circumnuclear region of the Seyfert galaxy NGC 3227. The physical and kinematical characteristics of the two gaseous components reported recently by Mediavilla & Arribas are discussed. One of the components seems to be directly related to activity. We propose that it represents gas streaming from the nucleus toward the north. The other component has more regular properties, appearing to be kinematically connected with the galactic mean velocity field. The broadening distribution inferred from this component is not centered around the broad-line region but next to the kinematical center derived from the ionized gas. This fact gives independent support to the offset location of the active nucleus with respect to the galaxy mass centroid. Despite this anomaly, the velocity field of NGC 3227 exhibits a rotational pattern. Fitting a simple model to the observed velocity field we found that the resulting parameters agree fairly well with those expected for spirals if warps on the galactic plane are allowed. This result is obtained assuming the kinematical center derived from the ionized gas. On the contrary, the broad-line region (BLR) occupies a fairly asymmetrical position in the velocity field and could hardly be taken as the kinematical center. The ionization structure is rather complex in NGC 3227. Analysis of the line flux ratios shows Seyfert and low-ionization nuclear emission-line region (LINER) emission characteristics in most of the central regions. This suggests that an active galactic nuclei (AGN)-like continuum (with varying ionization parameter) is likely to be the main source of ionization of the gas in these regions. However, H II-type emission is found over an extended area at about 300 pc from the optical nucleus, suggesting that young stars are responsible of the ionization of the gas in this region, which could be identified as an extranuclear starburst. Other zones, where thermal and AGN-like continua seem to contribute in a comparable manner to the ionization, are also found. In this respect, NGC 3227 is another example of a galaxy with composite AGN/H II ionization.
Arribas Santiago
Mediavilla Evencio
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