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

4.3. Results 121
the uncertainties of the least square fit and the reddening corrected Hβ intensity. Column 1 of
the table shows the wavelength and the name of the measured lines. The adopted reddening
curve, f(λ), normalized to Hβ, is given in column 2 of Table 4.4. The errors in the emission
lines, as explained in previous chapters, were obtained by propagating in quadrature the
observational errors in the emission line fluxes and the reddening constant uncertainties.
We have not taken into account errors in the theoretical intensities since they are much
lower than the observational ones. Finally, to compare the high quality of the data of J1657
achieved by Hägele et al. (2008) for Knot A, we have listed in Column 5 of Table 4.4 the
fractional error in the line intensities calculated as explained above.
4.3.2 Physical conditions of the gas
The physical conditions of the
ionized gas, including electron temperatures
and electron density,
have been derived from the emission
line data using the same procedures
as in Chapter §3, based
on the five-level statistical equilibrium
atom approximation in the
task temden, of the software package
IRAF. See Appendix B for a
detailed description of the relations
of the physical conditions of the gas
and ionic abundances. As usual,
we have taken as sources of error
the uncertainties associated with
Flux (erg s -1 cm -2 Å -1 )
5e-16
4e-16
1,1e-15
1e-15
9e-16
[OIII]
4363 Å
[OIII]
4363 Å
IIZw71 - Knot B
IIZw71 - Knot C
8e-16
4300 4320 4340 4360 4380 4400 4420
Wavelength (Å)
Figure 4.11: Detail of the rest-frame spectra of the knots
B and C of IIZw71 around the [Oiii] 4363 Å emission line.
the measurement of the emissionline
fluxes and the reddening correction,
and we have propagated them through our calculations.
Electron densities were derived in the four knots of IIZw71 from [Oii] λλ 3726 / 3729 Å
line ratios and in all the knots of both galaxies from [Sii] λλ 6717 / 6731 Å line ratios, which
are representative of the low-excitation zone of the ionized gas.
In all knots of IIZw71 the density values provide upper limits, which are lower when
the [Oii] lines are used. In the case of these lines, however, the spectral dispersion of our
data does not allow total resolution of the lines, and they were deconvolved by fitting two
Gaussian components as shown in Figure 4.8. The values for the electron density are lower
in both galaxies than the critical density for collisional de-excitation.