4 Line indices

We measured the Mg, Fe, and H$\beta$ line strength indices following Worthey et al. (1994) from flux calibrated spectra, as done in Paper I. Spectra were rebinned in the dispersion direction as well as in the radial direction as before. We indicate the average Iron index with <Fe> $\rm = (Fe_{5270}+Fe_{5335})/2$ (Gorgas et al. 1990) and the usual combined Magnesium-Iron index with $\rm [MgFe] = \sqrt{\rm Mg{\it b}<Fe>}$ (González 1993). We corrected all the measured indices for velocity dispersion broadening and calibrated our measurements to the Lick systems using stars from Faber et al. (1985). No focus correction was applied because atmospheric seeing was the dominant effect during observations (see Mehlert et al. 1998 for details). Errors on indices were derived from photon statistics and CCD read-out noise, and calibrated by means of Monte Carlo simulations. The measured values of H$\beta$, [MgFe], <Fe>, Mgb and Mg₂ are listed in Table 4 and plotted in Fig. 2. Figure 3 shows the comparison between the measurements of H$\beta$, [MgFe], <Fe>, Mgb and Mg₂ along the major axis of GMP 1176 and GMP 3792 obtained here and measurements obtained in Paper I. The agreement within the error is excellent. The data we obtained in this paper are fully consistent with those of Paper I. Indeed, Fig. 4 shows that the mean central values of $\sigma$, H$\beta$, [MgFe], <Fe>, Mgb and Mg₂ measured along the minor axes of the sample galaxies within an aperture of 2'' and those obtained along the corresponding major axes are in agreement within the errors, assessing that the new galaxy dataset is on the Lick system.

Figure 4: Central values of $\sigma$, H$\beta$, [MgFe], <Fe>, Mgb and Mg2 measured along major and minor axes and averaged within an aperture of 2''.