INVESTIGADORES
HÄGELE Guillermo Federico
artículos
Título:
The metal abundance of circumnuclear star-forming regions in early-type spirals. Spectrophotometric observations
Autor/es:
DÍAZ, ÁNGELES I.; TERLEVICH, ELENA; CASTELLANOS, MARCELO; HÄGELE, GUILLERMO F.
Revista:
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Editorial:
WILEY-BLACKWELL PUBLISHING, INC
Referencias:
Año: 2007 vol. 382 p. 251 - 269
ISSN:
0035-8711
Resumen:
We have obtained long-slit observations in the optical and near-infrared
of 12 circumnuclear HII regions [circumnuclear star-forming regions
(CNSFR)] in the early-type spiral galaxies NGC2903, 3351 and 3504 with
the aim of deriving their chemical abundances. Only for one of the
regions, the [SIII] λ6312Å was detected providing, together
with the nebular [SIII] lines at λλ9069, 9532Å, a
value of the electron temperature of . A semi-empirical method for the
derivation of abundances in the high metallicity regime is presented.
We obtain abundances which are comparable to those found in high
metallicity disc HII regions from direct measurements of electron
temperatures and consistent with solar values within the errors. The
region with the highest oxygen abundance is R3+R4 in NGC3504, 12 +
log(O/H) = 8.85, about 1.5 solar if the solar oxygen abundance is set at
the value derived by Asplund, Grevesse & Sauval, 12 +
log(O/H)solar = 8.66 +/- 0.05. Region R7 in NGC3351 has the
lowest oxygen abundance of the sample, about 0.6 times solar. In all the
observed CNSFR the O/H abundance is dominated by the
O+/H+ contribution, as is also the case for high
metallicity disc HII regions. For our observed regions, however, also
the S+/S2+ ratio is larger than one, contrary to
what is found in high metallicity disc HII regions for which, in
general, the sulphur abundances are dominated by
S2+/H+.
The derived N/O ratios are in average larger than those found in high
metallicity disc HII regions and they do not seem to follow the trend of
N/O versus O/H which marks the secondary behaviour of nitrogen. On the
other hand, the S/O ratios span a very narrow range between 0.6 and 0.8
of the solar value.
As compared to high metallicity disc HII regions, CNSFR show values of
the O23 and the N2 parameters whose distributions are shifted
to lower and higher values, respectively, hence, even though their
derived oxygen and sulphur abundances are similar, higher values would
in principle be obtained for the CNSFR if pure empirical methods were
used to estimate abundances. CNSFR also show lower ionization parameters
than their disc counterparts, as derived from the [SII]/[SIII]. Their
ionization structure also seems to be different with CNSFR showing
radiation field properties more similar to HII galaxies than to disc
high metallicity HII regions.