Determine the origin of the anomalous colour gradient in simulated clumps

Determine why the colour gradient of simulated clumps detected in high-mass galaxies is significantly steeper than the gradients measured in lower-mass galaxy bins, despite the best-fit models in those other bins having slopes statistically consistent with zero.

Background

The study measures radial colour gradients for observed clumps, the diffuse galaxy background, and simulated clumps across host galaxies of different stellar masses. The observed clumps generally become bluer with increasing galactocentric distance, whereas the simulated clumps are intended as a control population whose positions and properties should not produce strong intrinsic radial gradients.

For the highest-mass host galaxies, however, the simulated clumps exhibit a significant negative colour gradient, unlike the simulated-clump results in the lower-mass bins. The paper does not establish whether this arises from detection incompleteness, photometric contamination, properties of the simulated sample, or another systematic effect, leaving the interpretation of this control result unresolved.