a) Comparison of the systemic velocities obtained from NED and those estimated from the Hα+[N ii] radial velocities (see Sect. 3.2.1) for the objects in the sample. Error bars in the horizontal axis correspond to the velocity uncertainties provided by NED. These velocity uncertainties and the standard deviation of the averaged radial Hα+[N ii] velocities of each object were combined to calculate the error bars for the vertical axis. b) Comparison of the systemic velocities derived from Hα+[N ii] and [O iii] emission lines for the objects in the sample. Error bars in the horizontal axis correspond to the standard deviation of the averaged radial velocities to estimate for each object. Error bars for the vertical axis were calculated from the standard deviation of Hα+[N ii] and [O iii] radial velocities. In both panels, blue dots correspond to objects identified as galaxies in interaction (see Sect. 2.3 and Table A.1)