A spatially resolved study of ionized regions in galaxies at different ...

152 Conclusions and future work
other two, very similar. Knots B and C of IIZw71 have the same metallicity, within the errors,
but they are slightly lower than the abundances previously reported from measurements of
the integrated galaxy according to strong-line calibrations. The metallicity in the other two
fainter knots of this galaxy, where the temperature sensitive line could not be detected, was
estimated by means of different strong-line parameters. In all cases, the estimated abundances
are consistent with those derived for knots B and C by the direct method with the parameter
involving the sulphur lines providing the abundance closer to it. The rest of the parameters
slightly overestimate the oxygen abundance. The N/O abundance, as derived from the N2O2
parameter (the ratio of the [Nii] and [Oii] intensities), is remarkably constant over the ring
indicating that local pollution processes are absent. In the case of J1657, it has been found
that oxygen abundances of knot B and C are very close, with knot A showing a slightly higher
value. This behaviour is mirrored by the N/O ratio, but for the S/O and Ar/O, knots A and
B have a similar value, knot C being the one with a different value. Regarding the Ne/O
ratio, this is remarkably similar for all knots. Therefore, similar to what has been found for
the GEHR, no conclusive spatial variations of the total elemental abundances throughout
the two observed Hii galaxies are found, so the same considerations made above apply here
although at a different scale.
Although the underlying stellar population of the host galaxy of IIZw71 is detected in
the spectrum of the central knot (knot C), the similarity of the star formation histories in
the four knots, as deduced from the fitting of SSPs, as well as the derived metallicities, point
to a common chemical evolution of the polar ring. In the case of J1657, the star formation
history for the three knots derived from STARLIGHT are remarkably similar, with an old
population of about 8 Gyr presenting more than the 95% contribution to the mass fraction.
This result is somewhat unexpected and data on its surface brightness distribution would be
very valuable to explore further this finding.
Regarding IIZw71, for the differential velocity, we used the wavelength position of Hα
and [Sii] to measure an asymmetric rotation of the ring with a mean value of 85 km s −1 at
an optical radius of 20 ′′ . This gives a dynamical mass of (2.8 ± 0.2) × 10 9 M ⊙ and a M/L B
ratio of 3.9, close to the value reported previously by Reshetnikov and Combes (1994). The
kinematics of the ring is significantly affected by the expanding bubbles of ionised gas, which
in the case of knot C reaches 60 km s −1 .
Future work
Several results of this work have revealed interesting new paths for further investigation.
This will entail the obtention of new data in a much wider wavelength range and the 3D
modelling of Hii regions, among others.
NGC 5471 is truly a very amazing object which deserves more detailed analysis. We
have spectrophotometric data of this region with the aim to perform a kinematical study of