The impact of strong feedback on galaxy group scaling relations

TL;DR

The paper addresses whether strongly ejective AGN feedback can reproduce the gas content and X-ray properties of galaxy group halos in the $M_{500}\sim10^{13}$–$10^{14} M_\odot$ range. It analyzes 44 nearby groups from the X-GAP sample with uniform XMM-Newton data and compares measured $L_X$-$T$ and $L_X$-$M$ relations to FLAMINGO simulations across feedback strengths, including a strong-$fgas$ scenario. The main result is that highly ejective feedback models under-predict the X-ray luminosity at fixed temperature or mass, with a significance of $5.7σ$, while the fiducial FLAMINGO model remains consistent with the data; selection biases cannot fully account for the discrepancy. The study argues that calibrating feedback on baryon fractions is prone to large systematics and that observable scaling relations, especially $L_X$-$T$, provide a more robust diagnostic for the impact of AGN feedback on the hot atmospheres and the small-scale matter distribution, with implications for modeling galaxy groups and cosmology.

Abstract

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. Here we show that models involving highly ejective feedback are inconsistent with the scaling relations of local galaxy groups in the mass range $10^{13}-10^{14}M_\odot$. 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 ($5.7σ$). This conclusion is robust against 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 calibrating feedback models on baryon fractions is prone to systematic uncertainties and that observable scaling relations are better suited for this task.

Figures (3)

• Figure 1: Luminosity-mass (left) and luminosity-temperature (right) relations for X-GAP groups (colored symbols, see Table \ref{['tab:lxt']}). The solid curves show the relations obtained in various FLAMINGO runs (see B24). In the left-hand panel, the black diamonds show the luminosity-mass relation of optically selected groups in the eFEDS field Popesso:2024b.
• Figure 2: Predicted median temperatures (left) and number of selected groups (right) for FLAMINGO runs with varying feedback. Each data point shows the median and 16th/84th percentiles of simulated X-GAP-like mock samples. The orange vertical lines show the median temperature and the number of selected groups in the observed X-GAP sample. The numbers on top indicate the statistical significance of the difference with the data.
• Figure 3: $L_X-T$ relation as a function of $T_{500}$ (left) and $T_{300kpc}$ (right) for X-GAP (coloured symbols, see Table \ref{['tab:lxt']}) in comparison with literature measurements. In the left-hand panel, the magenta and green curves show the bias-corrected relations from Lovisari:2015 and Zou:2016, respectively. The orange curve in the right-hand panel is the $L_{X,500}-T_{300kpc}$ relation from XMM-XXL Giles:2016. In both panels, the blue curve shows the fit to the X-GAP $L_X-T$ relation, with the uncertainty in the mean indicated as the dark blue shaded area and the scatter around the mean indicated in light blue.