No direct coupling between bending of galaxy disc stellar age and light profiles

TL;DR

This study analyzes stellar age and brightness profiles in 44 face-on spiral galaxies, revealing that age upturns are not directly linked to surface brightness profiles and are likely due to early disc formation and inside-out quenching.

Contribution

It demonstrates that stellar age upturns occur in both type I and II galaxies and are not directly coupled with surface brightness profile types, challenging previous assumptions.

Findings

Age upturns observed in 17 out of 44 galaxies.

Age upturns are present in both type I and II profiles.

Light-weighted profiles show age upturns, but mass-weighted profiles do not.

Abstract

We study the stellar properties of 44 face-on spiral galaxies from the Calar Alto Legacy Integral Field Area survey via full spectrum fitting techniques. We compare the age profiles with the surface brightness distribution in order to highlight differences between profile types (type I, exponential profile; and II, down-bending profile). We observe an upturn ("U-shape") in the age profiles for 17 out of these 44 galaxies with reliable stellar information up to their outer parts. This "U-shape" is not a unique feature for type II galaxies but can be observed in type I as well. These findings suggest that the mechanisms shaping the surface brightness and stellar population distributions are not directly coupled. This upturn in age is only observable in the light-weighted profiles while it flattens out in the mass-weighted profiles. Given recent results on the outer parts of nearby systems and the results presented in this Letter, one of the most plausible explanations for the age upturn is an early formation of the entire disc ($\sim$~10~Gyr ago) followed by an inside-out quenching of the star formation.