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Data reduction

Data reduction was done at SAO with the MIDAS 94NOV software package. The context SPEC is adapted to the SAO data formats to perform an automatic reduction of the one-dimensional IPCS spectra (Kniazev [1994]). Corrections for flat field, azimuthal shift and two-channel modulation are applied to the IPCS spectra. Then, standard corrections for the atmospheric extinction, sky subtraction, and the instrumental response curve are done. All the IPCS spectra were taken mainly during rather poor, non-photometric weather conditions and, therefore, are presented in a relative count scale.

For the Calar Alto two-dimensional CCD data, the reduction included bias-dark correction, cosmic-ray removal and flat-field correction. 1-D spectra are extracted by adding 3-4 consecutive CCD rows centered at the object intensity peak. After sky subtraction they are converted to linear scale and corrections for atmospheric extinction and flux calibration are applied. For the flux calibration we use the mean response curve obtained from observations of two standard stars. Calar Alto CCD spectra are presented on an absolute flux scale.

The redshifts and line fluxes are measured applying Gaussian fits to the line profiles. The average redshift of each galaxy is derived from the observed wavelengths of all prominent individual emission lines excluding [O II]$\lambda$3727 Å, which is outside of the region where the wavelength calibration curve is well determined. The typical internal redshift errors are estimated to be less than 0.0001 for the Calar Alto emission-line spectra and less than 0.0003 for the 6m emission-line spectra. For galaxies with absorption features the redshift errors are within $\sim$ 0.0005.

The emission line fluxes are derived as the sum of the pixel intensities inside the line region using standard MIDAS program tools. For all but one spectrum, the individual emission line fluxes of the H$\alpha$, [N II] $\lambda\lambda$6548,6583 Å and [S II] $\lambda\lambda$6716,6731 Å line blends are obtained by summing of pixel intensities over the total blend and then modelling the individual line fluxes using Gaussian fitting.