Measuring the CGM to the virial radius with LEM mock observations

The Astro2020 Decadal Survey has clearly identified the mapping of the circumgalactic medium (CGM, gaseous halo around galaxies that extends to the virial radius) as a key objective. The Line Emission Mapper (LEM) is an X-ray Probe concept for the 2030s that will address this, and many other outstanding questions concerning structure formation in the Universe. We demonstrate the transformative capabilities of LEM to trace the CGM and provide conclusive answers on the galaxy formation and interplay of stellar and AGN feedback processes.

Based on realistic mock observations that include the foreground and background components, we find that LEM can - for the first time - measure the surface brightness of the hot gas of individual galaxies (Milky Way size) out to R₅₀₀. We show that we can even recover observables of the different feedback prescriptions included in the IllustrisTNG, Eagle, and Simba hydrodynamical simulations, such as substructure in the gas, or line ratio profiles. We derive temperature and velocity maps from spectral fitting for some individual galaxies to demonstrate the detectability of rotation features, AGN outbursts, and enrichment processes, which has never been observed for Milky Way-sized halos.