  Galactic stellar discs, such as that of the Milky Way, have usually a complex
structure consisting of a thin and a thick component. 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 populations of
the thick disc components in external galaxies. Here we investigate three
edge-on early-type disc galaxies in the Fornax cluster IC335, NGC1380A, NGC1381
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
outermost thick-disc dominated regions demonstrate remarkably old ages and a
low metallicity. We interpret these findings as a consequence of star formation
quenching in the outermost regions of the discs due to 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 starvation.

Astrophysics of Galaxies