Exploring the outskirts of the EAGLE disc galaxies

Observations show that the surface brightness of disc galaxies can be well-described by a single exponential (TI), up-bending (TIII) or down-bending (TII) profiles in the outskirts. Here we characterize the mass surface densities of simulated late-type galaxies from the EAGLE project according to their distribution of mono-age stellar populations, the star formation activity and angular momentum content. We find that the inner scale-lengths of TII galaxies correlate with their stellar spin parameter $\lambda$, while those with TI and TIII profiles show a correlation only for $\lambda>0.35$. The outer scale-lengths of TII and TIII discs show a positive trend with $\lambda$, albeit weaker for the latter. TII discs prefer fast rotator galaxies. With regards to the stellar age distribution, negative and U-shape age profiles are the most common for all disc types. Positive age profiles are determined by a more significant contributions of young stars in the central regions, which decrease rapidly in the outer parts. TII discs prefer relative higher contributions of old stars compared to other mono-age populations across the discs whereas TIII discs become progressively more dominated by intermediate age (2-6 Gyrs) stars for increasing radius. The change in slope of the age profiles is located after the break of the mass surface density. We find evidence of larger flaring for the old stellar populations in TI and TIII systems compared to TII. Overall, the relative distributions of mono-age stellar populations and the dependence of star formation on radius is found to modulate the different disc types and age profiles.