Optical spectra are presented for all program objects in Fig. 4 (click here). They have all been corrected for telluric absorption, though some of the corrections were not as good as we would have thought.
Figure 4: The spectra of VLIRGs f 
vs. 
.
The units of the vertical axis are ergs s -1 cm -2
Å-1
Figure 4: Continued
Figure 4: Continued
Figure 4: Continued
Figure 5: Example of Gaussian fit for
H 
+[NII] 
emission. Three narrow Gaussian components are used
The pluses are observed data
Figure 6: Example of multi-component fit for the galaxies with
strong Balmer absorption. One Lorentz absorption and
one narrow Gaussian emission components are used
Figure 7: Example of Gaussian fit for Seyfert 1 s. One broad and
three narrow Gaussian emission components are used
Figure 8: Distribution of redshift differences between our
data and the 2 Jy redshift catalog
The measurements of emission line, absorption line and continuum strengths were performed within
the IRAF environment using tasks (SPLOT and SPECFIT).
For isolated emission lines such as
, 
and 
, both Gaussian fitting and direct integral methods were used.
For the blended lines such as 
, 
, and 
double lines, we employed a multi-Gaussian component method using task SPECFIT,
to deblend them. There are three parameters for each
Gaussian component: the central wavelength, the total flux and width of the emission line;
and two parameters for each continuum component: the flux and the slope. In
order to speed up the convergence, some limit conditions were adopted. For example,
we fixed the center wavelengths of several components relate to one another.
In Fig. 5 (click here), for example, we used the simplex
algorithm for the fitting and obtained the result via a chi-square
minimization process. As for the spectra with obvious
absorption indicating an underlying stellar population, a similar method was used.
Because of the coexistence of emission and absorption, one emission and one
absorption component were used for the fitting. The
wide absorption wings due to stellar populations often cause the absorption to be overestimated
if Gaussian model is adopted.
To solve this problem, we adopted the Lorentz model as shown in
Fig. 6 (click here), and the results
seem better. Some of our sample galaxies are Seyfert-like, and their spectra could not fitted well
with only single Gaussian component for each of , . In those case, we combined one
narrow 
and
one broad 
Gaussian
component as shown in Fig. 7 (click here).
The relative emission-line fluxes are listed in Table 3
for all objects. The typical uncertainty in these measurement
is about 10%. Colons (:) and semicolons (;) indicate values with relative uncertainties
at about 30% and 50% respectively. For the line , we could not obtain a value with an uncertainty of less than 20%,
because it was at the blue end of the spectra, which can be affected by the
low Q.E., lower S/N and poor flux calibration.
In some cases, lines were heavily
affected by the nearby emission lines 
which could increase
the uncertainty. The telluric absorption bands
and 
was
also enlarge the uncertainty in the measurement
of lines near them, despite
the corrections performed. The double lines
,
could sometimes be separated,
but when this was not possible, only the combined values are given.
The measured redshifts, observed fluxes,
equivalence widths of emission lines, NaID absorption lines and absorption lines, and two
continuum fluxes (at 
and 
) are listed in
Table 4.
The typical uncertainty in the measured
fluxes was 15%, as the
lines often had to be deblended from an overlapping [NII] emission line.
Finally, we compare our measured redshifts with those of corresponding sources in the 2 Jy redshift sample. The distribution of redshift differences is plotted in Fig. 8 (click here). The mean redshift difference is 0.000054 and scatter is 0.00038. This means that our measurements agree well with these of the 2 Jy catalogue.