The impact of strong feedback on galaxy group scaling relations

Feedback from active supermassive black holes alters the distribution of matter in the Universe by injecting energy in the neighbouring hot gaseous medium, which leads to ejection of gas from the halos of galaxy groups and massive galaxies. Recent cosmological simulations such as FLAMINGO calibrate their feedback model on the baryon fractions of galaxy groups to tune the efficiency of gas ejection. However, recent observational constraints from optically selected groups and the kinetic Sunyaev–Zel’dovich effect yield lower baryon fractions than previous studies, which indicates that feedback may be more ejective than previously thought. In this work, we confirm that the scaling relations of local galaxy groups in the mass range 10 13 − 10 14 M ⊙ favour the fiducial FLAMINGO feedback calibration. We study the X-ray luminosity–temperature relation in a sample of 44 galaxy groups with high-quality XMM-Newton observations. We show that highly ejective models under-predict the luminosity of galaxy groups at fixed mass at high significance (5.7 σ ). This discrepancy cannot be explained by selection effects and is obtained from directly measurable and minimally correlated quantities. We point out that turning observable quantities into gas fraction estimates is challenging, especially in the context of stacking large samples of heterogeneous systems. We argue that validating feedback models against observable scaling relations is necessary to warrant the validity of feedback implementations in cosmological simulations.