Bibcode
DOI
Arribas, S.; Mediavilla, E.
Referencia bibliográfica
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 437, no. 1, p. 149-161
Fecha de publicación:
12
1994
Revista
Número de citas
26
Número de citas referidas
22
Descripción
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.