The imprint of the thick stellar disc in the mid-plane of three early-type edge-on galaxies in the Fornax cluster

Abstract

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.

12 pages, 7 figures; Accepted for publication in MNRAS

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• The vertical structure of the spiral galaxy NGC 3501: first stages of the formation of a thin metal-rich disc
• Star formation in outer rings of S0 galaxies. IV. NGC 254 -- a double-ringed S0 with gas counter-rotation
• Relatively young thick disks in star-forming late-type galaxies
• A prediction on the age of thick discs as a function of the stellar mass of the host galaxy
• An Integral Field Spectroscopy Study Of Thin And Thick Discs In IC 2531