Other
Scientific paper
Aug 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003basbr..23r.150f&link_type=abstract
Boletim da Sociedade Astronômica Brasileira (ISSN 0101-3440), vol.23, no.1, p.150-151
Other
1
Scientific paper
The chemical abundance of the circumnuclear gas in AGN's give us clues about its origin and affects the observed emission-line ratios. We investigate this aspect using long-slit spectra obtained along the extended emission line region (EELR) of 18 Seyfert 2 galaxies, exploring the dependence of the [NII]6548,84/[OII]3727 emission line ratio in the gas chemical abundance. We have used the MAPPINGS Ic photoionization code (Binette et al. 1996) to model the ionization of the EELR by an AGN continuum in three possible scenarios for the emitting gas clouds: all clouds are matter-bounded (MB); all clouds are ionization-bounded (IB); there is a mixture of MB and IB clouds. We found that the range of observed [NII]/[OII] line ratios can only be reproduced by a range of chemical abundances, from 0.5 (O/H)¤ up to 3 (O/H)¤. Parameters such as the gas density and shape of the ionizing continuum play only a secondary role in reproducing the observed variations. Most galaxies show nuclear (O/H) abundances which are comparable with those of non-active spiral galaxies obtained in previous studies from extrapolations of HII regions abundances gradients along the body of the galaxy. Nevertheless, the abundance gradients obtained for the EELR are, on average, steeper than those observed in non-active galaxies. Nitrogen shows a secondary behaviour, in agreement with previous findings. A new calibration is proposed to recover the gas metallicity from the [NII]6548,84/[OII]3727 line ratio, which is compared with other calibrations proposed by previous works.
Fraquelli Henrique A.
Storchi-Bergmann Thaisa
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