Ionized gas in E/S0 galaxies with dust lanes

We report the results of multicolour observations of 30 E/S0 galaxies with dust lanes. For each galaxy we obtained broad-band images and narrow-band images using interference filters isolating the H alpha+[N ii] emission lines to derive the amount and morphology of dust and ionized gas. To improve the wavelength coverage we retrieved data from the Sloan Digital Sky Survey and Two Micron All Sky Survey and combined these with our data. Ionized gas is detected in 25 galaxies and shows in most cases a smooth morphology, although knots and filamentary structure are also observed in some objects. The extended gas distribution closely follows the dust structure, with a clear correlation between the mass of both components. An extinction law by the extragalactic dust in the dark lanes is derived and is used to estimate the dust content of the galaxies. The derived extinction law is used to correct the measured colours for intrinsic dust extinction and the data are fitted with a stellar population synthesis model. We find that the H alpha emission and colours of most objects are consistent with the presence of an 'old' stellar population (similar to 10 Gyr) and a small fraction of a 'young' population (similar to 10-100 Myr). To check this we closely examine NGC 5363, for which archival Spitzer/Infrared Array Camera and Galaxy Evolution Explorer data are available, as a representative dust-lane E/S0 galaxy of the sample.