Colour distributions in E-S0 galaxies.

Abstract

Colours distributions have been studied in 12 S0 galaxies, most of these nearly edge-on, from high resolution frames obtained at the CFHT and the Pic du Midi 2 m telescope, supplemented for some purposes by low resolution frames from the Observatoire de Haute Provence 120 cm telescope. Great attention has been given to reduce the effects of “differential seeing", resulting from different PSF's in the two frames needed for a colour measurement. Errors from various sources, and their effect upon measured quantities, have been evaluated from the study of pseudo-colours (obtained by applying our measuring techniques to pair of frames taken in the same passband), and from the comparison of colours data from our various series. Data are given about the following topics: – Radial isophotal colour profiles, leading to reference colours at re and gradients in 4 colour indices (except for missing data); – Reference colours and gradients in possibly dustless regions of nearly pure bulge or disk, allowing a comparison between the two components; – Dust patterns, seen in 7 objects; – Systematic differences between major and minor axis colours upon isophotal contours (outside dust patterns). Both a redder or bluer major axis are encountered depending upon the object, or the central distance in a given object. The observations may sometimes be explained by local dust concentration in disks. In other cases population differences between spheroidal and disk components should be invoked; – Asymmetries in light and colour distributions along the minor axis in 3 objects, due to dust concentrated in the disk; – Correlations between ring structure and major axis colour profiles.