LAUSR

Galactic stellar discs, such as that of the Milky Way consisting of a thin and a thick component, have usually a complex structure. The study of galactic disc substructures and their differences can shed light on the galaxy assembling processes and their evolution. However, due to observational difficulties there is a lack of information about the stellar population of the thick disc component in the external galaxies. Here we investigate three edge-on early-type disc galaxies in the Fornax cluster (IC 335, NGC 1380A, NGC 1381) by using publicly available photometrical data and our new deep long-slit spectroscopy along galactic mid-planes obtained with the 10-m SALT telescope. We report that significant changes of the stellar population properties beyond the radius where photometrical profiles demonstrate a knee are caused by an increasing thick disc contribution. Stellar population properties in the the outermost thick-disc dominated regions demonstrate remarkably old ages and low metallicity. We interpret these findings as a consequence of star formation quenching in the outermost regions of the discs due to the ram pressure gas stripping from the disc periphery at the beginning of the cluster assembly while subsequent star formation occurring in the inner discs being gradually extinguished by the starvation.