Spatial distribution of the X-ray emission from the hot gas around a massive dark matter halo. The dashed circle indicates the size of r_200m. At large radii, the halo is connected to and accreting smaller nearby halos from cosmic filaments. This map is produced using gas particles from a 20 × 20 × 20 Mpc³ box around the id=32 halo in the z = 0 snapshot of the TNG300-1 simulation (see Sect. 4 for the details of map creation). The central halo is in a mass M_500c = 2.8 × 10¹⁴ M_⊙ and an r_200m of 2.5 Mpc. Short arrows mark the accretion shock, i.e., the boundary between shock-heated gas and the cool intergalactic medium.