Growth of Ex-situ Diffuse Intragroup Light in Simulated Galaxy Groups

Abstract: Deep surface photometry reveals a faint, diffuse baryonic component in a significant fraction of galaxy groups, permeating the intragroup space. This intragroup light (IGL) is primarily formed by stars removed from their host galaxies through gravitational interactions and now drifting freely, unbound to any galaxy. We conduct a detailed analysis to investigate how various physical parameters of galaxy groups influence the formation of ex-situ IGL during the earliest stages of group assembly, and to explore their correlations with this component. Additionally, we evaluate the potential of the IGL as a luminous tracer of the total mass distribution in galaxy groups, with particular focus on systems that are far from being dynamically relaxed. We use controlled numerical simulations of 100 low-mass galaxy groups spanning a range of masses and numbers of constituent galaxies. We show that the IGL typically begins to form in significant amounts after the turnaround epoch (redshift ~ 0.85), increasing steadily thereafter. We observe a sublinear relationship between the masses of this component and the brightest group galaxy, indicating intertwined formation histories but differing growth rates, which suggests that other group members may also significantly contribute to the diffuse light. Additionally, we observe indications that IGL formation is enhanced in groups with lower internal velocity dispersions, suggesting that gravitational interactions among member galaxies become more effective when their relative velocities are reduced. Two-thirds of our groups reveal significant alignment between the radial surface density profiles of the total and IGL mass, with fractional discrepancies below 25%. This supports the notion that this diffuse and faint baryonic component serves as a reliable tracer of the total gravitational potential in galaxy aggregations, regardless of their dynamical state.