The resulting 
map is shown on Figure 5b.
For each of the 21 bins where the STNEI model provides a good description of the observed spectra,
we evaluated the confidence regions in the 
plane. The
results indicate a value of the ionization time 
yr
cm
in 18 bins,
while values compatible with the range 
can be found in the remaining 3 cases.
The low 
values resulting in the other 18 bins
is very difficult to interpret on the basis of our physical expectations, as
discussed in section 3.2.c. In fact, we recall that, since our
measurement is actually an estimate of 
, a ionization time
less than 10 yr cm can be regarded as unrealistic.
Hence, in the next section, we will focus
our attention only on the 3 bins
which have a 99% confidence range which
overlaps with the physically plausible range 
in yr
cm. In table 3, we
list the 3 bins which satisfy this criterion (hereafter the T3 bins),
and which therefore provide the most reliable numbers for the derived
quantities.