X-ray Emission From Hot Gas in Galaxy Groups and Clusters in Simba

We examine X-ray scaling relations for massive haloes (⁠M500>1012.3M⊙⁠) in the simba galaxy formation simulation. The X-ray luminosity, L_X versus M₅₀₀ has power-law slopes ≈53 and ≈83 above and below 1013.5M⊙⁠, deviating from the self-similarity increasingly to low masses. T_X − M₅₀₀ is self-similar above this mass, and slightly shallower below it. Comparing simba to observed T_X scalings, we find that L_X, L_X-weighted [Fe/H], and entropies at 0.1R₂₀₀ (S_0.1) and R₅₀₀ (S₅₀₀) all match reasonably well. S₅₀₀ − T_X is consistent with self-similar expectations, but S_0.1 − T_X is shallower at lower T_X, suggesting the dominant form of heating moves from gravitational shocks in the outskirts to non-gravitational feedback in the cores of smaller groups. simba matches observations of L_X versus central galaxy stellar mass M_*, predicting the additional trend that star-forming galaxies have higher L_X(M_*). Electron density profiles for M500>1014M⊙ haloes show a ∼0.1R₂₀₀ core, but the core is larger at lower masses. T_X are reasonably matched to observations, but entropy profiles are too flat versus observations for intermediate-mass haloes, with S_core ≈ 200–400 keV cm². simba’s [Fe/H] profile matches observations in the core but overenriches larger radii. We demonstrate that Simba’s bipolar jet AGN feedback is most responsible for increasingly evacuating lower-mass haloes, but the profile comparisons suggest this may be too drastic in the inner regions.