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

Abstract

Context. Deep surface photometry has revealed the presence of a faint and diffuse baryonic component permeating the intragroup space in a significant fraction of galaxy groups. This intragroup light (IGL) is primarily formed by stars that are removed from their host galaxies through gravitational interactions and now drift freely, unbound to any particular galaxy. Aims. We conducted 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 the mass and fractional abundance of this component. Additionally, we evaluated the potential of the IGL as a luminous tracer of the total mass distribution in galaxy groups, with a particular focus on systems that are far from dynamically relaxed. Methods. We used controlled numerical simulations of 100 low-mass galaxy groups spanning a range of masses and numbers of constituent galaxies to track the formation and evolution of IGL during the earliest pre-virialization stages of these systems. Results. We show that the IGL typically begins to form in significant amounts after the turnaround epoch, which in our simulated groups occurs at a median redshift (z̄_ta) of ∼0.85, increasing steadily thereafter. We observe a sub-linear relationship between the masses of this component and the brightest group galaxy, which indicates intertwined formation histories but differing growth rates. This 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, which suggests that gravitational interactions between member galaxies become more efficient when their relative velocities are reduced. For two-thirds of our groups, the radial surface density profiles of the total and IGL mass are significantly aligned, 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. However, the results also indicate that the degree of similarity depends on the viewing direction.