Two-dimensional line-strength maps in three well-studied early-type galaxies

Integral field spectroscopy has been obtained for the nuclear regions of th ree large, well-studied, early-type galaxies. From these spectra we have ob tained line-strength maps for about 20 absorption lines, mostly belonging t o the Lick system. An extensive comparison with multilenslet spectroscopy s hows that accurate kinematic maps can be obtained, and also reproducible li ne-strength maps. Comparison with long-slit spectroscopy also produces good agreement. We show that Mg is enhanced with respect to Fe in the inner disc of one of the three galaxies studied, the Sombrero. [Mg/Fe] there is larger than in t he rest of the bulge. The large values of Mg/Fe in the central disc are con sistent with the centres of other early-type galaxies, and not with large d iscs, like the disc of our Galaxy, where [Mg/Fe] similar to 0. We confirm w ith this observation a recent result of Worthey: that Mg/Fe is determined o nly by the central kinetic energy, or escape velocity, of the stars, and no t by the formation time-scale of the stars. A stellar population analysis using the models of Vazdekis et al. shows tha t our observed H gamma agrees well with what is predicted based on the othe r lines. Given the fact that H beta is often contaminated by emission lines , we confirm the statement of Worthey & Ottaviani, Kuntschner & Davies and others that if one tries to measure ages of galaxies, H gamma is a much bet ter index to use than H beta. Using the line strength of the Ca ii IR tripl et as an indicator of the abundance of Ca, we find that Ca follows Fe, and not Mg, in these galaxies. This is peculiar, given the fact that Ca is an a lpha element. Finally, by combining the results of this paper with those of Vazdekis et al., we find that the line-strength gradients in the three gal axies are primarily caused by variations in metallicity.