Redshift Evolution of Galaxy Group X-ray Properties in Simba

Abstract

We examine the evolution of intragroup gas X-ray scaling relations for group-sized halos ($M_{500}=10^{12.3-15}M_{\odot}$) in the Simba galaxy formation simulation. X-ray luminosity $L_X$ vs $M_{500}$ shows increasing deviation from self-similarity from $z=3\to 0$, with $M_{500}<10^{13.5} M_{\odot}$ halos exhibiting a large reduction in $L_X$ and slight increase in X-ray luminosity-weighted temperature $T_X$. These shifts are driven by a strong drop in $f_{\rm gas}$ with time for these halos, and coincides with the onset of black hole jet feedback in these systems at $z\sim 1.5$ in Simba. The connection with black hole feedback is corroborated by $f_{BH}\equiv M_{BH}/M_{500}$ in $M_{500}<10^{13.5} M_{\odot}$ halos being strongly anti-correlated with $L_X$ and $f_{\rm gas}$ at $z\la 1.5$. This is further reflected in the scatter of $L_X-T_X$: halos with small $f_{BH}$ lie near self-similarity, while those with the highest $f_{BH}$ lie furthest below. Turning off jet feedback results in mostly self-similar behaviour down to $z=0$. For the X-ray weighted metallicity $Z_X$, 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 $M_{500}<10^{13.5} M_{\odot}$. This argues that 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.