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

3.4. Results 81
ID log L(bb) I(bb) a -EW(bb)
(erg · s −1 )
Å
Knot A 38.58 ± 0.04 20.3 ± 1.7 14.0 ± 1.2
Knot B 37.41 ± 0.06 27.4 ± 3.5 25.5 ± 3.3
Knot C 37.90 ± 0.05 22.7 ± 2.8 16.4 ± 2.9
Knot D · · · · · · · · ·
a In units of 100 · I(Hβ)
Table 3.3: Luminosities, relative intensities and equivalent widths of the Wolf-Rayet features measured
on the integrated spectra of four knots at 4650 Å (blue bump, bb). All quantities have been
corrected for reddening.
3.4.8 Physical properties and chemical abundances from the integrated
spectra
In order to study the mean properties of the Hii complex, several integrated spectra were
obtained from the PPak-field. As we have seen in Figure 3.14, there are four main Hα intense
knots. These structures have enough signal-to-noise to perform an analysis of the physical
properties of the gas and their abundances. Unfortunately, auroral lines with acceptable
errors were not found in individual fibers; enough signal-to-noise to measure these weak lines
was achieved only in the integrated spectrum of each knot.
In section 3.3.8 we have seen that a complete mosaic of 993 spectra was accomplished for
the blue range (3700-7000 Å), while for the red data (7000-10000 Å) we had only one pointing
of 331 spectra, since there was a problem with the guiding and de-rotator. Therefore, in order
to take advantage of all the relevant emission lines available, we had to build the integrated
spectrum for each knot from the first blue and red pointing. Since the FOV for one pointing
is not completely covered by all the fibers (see Figure 3.8, for example), we cannot expect to
obtain absolute fluxes. Nevertheless, we can assume that the relative intensities of the lines
should be similar, so that the derived properties and abundances should not be different
within the errors.
The spatial limits of each of the four knots were defined in the Hα map by means of
visual inspection with the help of isocontour plots. The limit contour is at the 20-30% of
the maximum peak. In order to have a better definition, we used the Hα map built from
the mosaic (3 pointings). Then, once the knots were defined, we co-added all the fibers
belonging to each knot in the mosaic exposure, obtaining four, absolute flux calibrated,
integrated spectra. It is important to ensure that the integrated spectra of each knot in the
one dithering exposure is built coming from exactly the same area. Performing this task
is another advantage of IFU data, since each fiber is perfectly identified. From the mosaic
integrated spectra we had the ID of the fibers, and therefore the fibers coming from each
of the three ditherings. Thus, we co-added the fibers coming from the first blue and red