X-ray emission from hot gas in galaxy groups and clusters in SIMBA

Abstract

We examine X-ray scaling relations for massive haloes (M500 > 1012.3 M) in the SIMBA galaxy formation simulation. The X-ray luminosity, LX versus M500 has power-law slopes ≈5 3 and ≈8 3 above and below 1013.5 M, deviating from the self-similarity increasingly to low masses. TX − M500 is self-similar above this mass, and slightly shallower below it. Comparing SIMBA to observed TX scalings, we find that LX, LX-weighted [Fe/H], and entropies at 0.1R200 (S0.1) and R500 (S500) all match reasonably well. S500 − TX is consistent with self-similar expectations, but S0.1 − TX is shallower at lower TX, 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 LX versus central galaxy stellar mass M∗, predicting the additional trend that star-forming galaxies have higher LX(M∗). Electron density profiles for M500 > 1014 M haloes show a ∼0.1R200 core, but the core is larger at lower masses. TX are reasonably matched to observations, but entropy profiles are too flat versus observations for intermediate-mass haloes, with Score ≈ 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.