Simulations of Galaxy Groups Observed by the Line Emission Mapper

In between massive clusters and typical galaxies, lie galaxy groups. Like the intracluster medium, the intragroup medium (IGrM) is dominated by X-ray emitting gas, yet the IGrM differs in several fundamental ways. The IGrM is cooler and often dominated by line as opposed to continuum emission. Groups harbor central and satellite galaxies that are more often star forming and therefore capable of supernova-driven superwinds. The IGrM has a greater proportion of cool, T<10⁵ K gas, likely indicating efficient cooling of X-ray emitting gas. All together, these properties make groups and their IGrM an intriguing target for the proposed Line Emission Mapper (LEM) probe-level mission. We demonstrate the capability of LEM to map nearby galaxy groups in exquisite detail owing to its excellent spectral resolution, large collecting area, and moderate angular resolution using state-of-the-art simulations. We show results from three leading simulations: EAGLE, IllustrisTNG, and SIMBA. LEM would revolutionize the observations of groups by mapping diverse structures, measuring sub-100 km/s kinematics, and tracing the abundance ratios across the IGrM. We argue that groups will provide some of the richest datasets that LEM will observe due to the IGrM’s brightness and complexity.