Redshift evolution of galaxy group X-ray properties in the SIMBA simulations

Abstract

We examine the evolution of intragroup gas rest-frame X-ray scaling relations for group-sized haloes (M500 = 1012.3–1015 M) in the SIMBA galaxy formation simulation. X-ray luminosity LX versus M500 shows increasing deviation from self-similarity from z = 3 → 0, with M500 < 1013.5 M haloes exhibiting a large reduction in LX and slight increase in X-ray luminosity-weighted temperature TX. These shifts are driven by a strong drop in fgas with time for these haloes, and coincides with the onset of SIMBA’s black hole (BH) jet feedback, occurring when MBH > 107.5 M and Eddington ratio <0.2, in group haloes at z ∼ 1.5. The connection with BH feedback is corroborated by fBH ≡ MBH/M500 in M500 < 1013.5 M haloes being strongly anticorrelated with LX and fgas at z 1.5. This is further reflected in the scatter of LX − TX: haloes with small fBH lie near self-similarity, while those with the highest fBH lie furthest below. Turning off jet feedback results in mostly self-similar behaviour down to z = 0. For the X-ray weighted metallicity ZX, stellar feedback impacts the enrichment of halo gas. Finally, halo profiles show that jet feedback flattens the electron density and entropy profiles, and introduces a core in X-ray surface brightness, particularly at M500 < 1013.5 M. This argues that in SIMBA, intragroup X-ray evolution is largely driven by jet feedback removing hot gas from the cores of massive groups, and expelling gas altogether in less massive groups.