The lenticular galaxy NGC 3607 : stellar population , metallicity and ionised gas

Context. The investigation of the dominant formation mechanism of early-type galaxies. Aims. In this work we derive clues to the formation scenario and ionisation source of the lenticular galaxy NGC3607 by means of metallicity gradients, stellar population and emission lines properties. Methods. We work with long-slit spectroscopy from which we (i) study the radial distribution of the equivalent widths of conspicuous metallic absorption features, (ii) infer on the star-formation history (with a stellar population synthesis algorithm), and (iii) investigate the ionisation source responsible for a few strong emission lines. Results. Negative radial gradients are observed for most of the absorption features of NGC3607. Compared to the external parts, the central region has a deficiency of alpha elements and higher metallicity, which implies different star-formation histories in both regions. At least three star formation episodes are detected, with ages within 1-13Gyr. The dynamical mass and the Mg2 gradient slope are consistent with mergers being important contributors to the formation mechanism of NGC3607. Emission-line ratios indicate the presence of a LINER at the centre of NGC3607. Contribution of hot, old stars to the gas ionisation outside the central region is detected. Conclusions. Evidence drawn from this work suggest small mergers as important contributors to the formation of NGC3607, a scenario consistent with the star-formation episodes.