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3 Data reduction

As in Papers I to III, standard pre-processing was applied to the raw data, up to the rebinning in wavelength. The galaxy centers (r=0) were determined by a Gaussian fitting to a limited range ($\simeq 12''$) around the intensity peak. In the outer regions, cosmic-ray hits were removed with a median filter, and adjacent lines were combined with a variable weighting function (a Gaussian continuously wider faintward). A Fourier-Fitting technique determined the central velocity dispersion $\sigma_0$ and, when possible, the radial profile $\sigma(r)$ of the dispersion, together with the projected rotation curve V(r) along the major axis. A two-pass mode (described in Paper I) allowed to remove cosmics on the inner lines, where the spatial resolution must be preserved. We adopted as the systemic velocity the value measured at r=0. Whenever possible, we have determined the maximum rotation velocity $V_{\rm max}$, as the mean of representative values on the opposite semi-axes.


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