Exploring the link between galaxy assembly and dark matter halo assembly in IllustrisTNG: insights from the Mutual Information

ABSTRACT We employed Mutual Information (MI) analysis to investigate the relationship between galaxy properties and the assembly history of their host dark matter (DM) haloes from the IllustrisTNG simulations. Focusing on central and satellite galaxies with stellar masses between $10^{9} \, \mathrm{ and} \, 10^{11.5}$ h$^{-1}$ ${\rm M}_{\odot }\,$, we examined the correlation between halo assembly time and galaxy assembly time, specific star formation rate (sSFR), colour $(g-i)$, and galaxy formation efficiency $F_\star$. Our results indicate a strong correlation between $F_\star$ and the halo assembly time for low-mass central galaxies, suggesting a co-evolutionary relationship. In contrast, sSFR and colour $(g-i)$ exhibit weaker correlations with halo assembly time, indicating that additional factors should influence these galaxy properties. Satellite galaxies show negligible correlation between their properties and halo assembly time, highlighting the impact of environmental processes on their evolution. We further extended our analysis to cluster observables, including the magnitude gap, the satellite richness, and the distances to the satellites. Although these cluster properties display weak overall correlations with halo assembly time, the richness consistently increases with stellar mass. This trend suggests that richness is more closely linked to formation history in more massive haloes, where satellite accretion dominates the growth of their host DM haloes. These findings establish $F_\star$ as a more sensitive indicator of halo assembly history than colour $(g-i)$, sSFR, or cluster observables, offering new insights into the complex interplay between galaxy evolution and the hierarchical growth of their host dark matter haloes.