Exploring the outskirts of the EAGLE disc galaxies

TL;DR

This study analyzes simulated EAGLE disc galaxies to understand how their surface brightness profiles, stellar age distributions, and angular momentum relate, revealing correlations and differences among various disc types.

Contribution

It provides new insights into the connection between galaxy angular momentum, stellar age profiles, and surface density structures in simulated galaxies.

Findings

Inner scale-lengths correlate with stellar spin parameter {1}

TII discs favor fast rotating galaxies

Old stellar populations show larger flaring in TIII systems

Abstract

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 a clear correlation between the inner scale-lengths and the stellar spin parameter, {\lambda}, for all three disc types with {\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 rotating 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 TIII systems compared to TI and TII, which could indicate the action of other processes. Overall, the relative distributions of mono-age stellar populations and the dependence of the star formation activity on radius are found to shape the different disc types and age profiles.