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

Universidade Federal do Rio Grande do Sul (UFRGS), Instituto de Física, Departamento de Astronomia, Brazil e-mail: [maurogr;mgp;charles]@if.ufrgs.br

Received: 11 December 2008
Accepted: 14 July 2009

Abstract

Aims. In this work we derive clues to the formation scenario and ionisation source of the lenticular galaxy NGC 3607 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) make inferences about 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 NGC 3607. 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 1–13 Gyr. The dynamical mass and the Mg₂ gradient slope are consistent with mergers being important contributors to the formation mechanism of NGC 3607, a scenario consistent with the star formation episodes.. Emission-line ratios indicate a LINER at the centre of NGC 3607. Contribution of hot, old stars to the gas ionisation outside the central region is detected.