Speaker
Description
X-ray emission from the hot gaseous atmospheres of galaxy groups and clusters is a sensitive tracer of the non-gravitational processes that redistribute the matter within and around dark matter halos. In particular, energetic processes associated with accreting matter onto supermassive black holes, known as active galactic nuclei (AGN) feedback, are currently the favoured scenario for ejecting gas outside the virial regions of groups and clusters of galaxies, ultimately reshaping the matter distribution of the Universe on small scales. At $R_{\mathrm{200}}$, gas fraction measurements are scarce due to the limited sensitivity of X-ray instruments. Cosmological hydrodynamical simulations, on the other hand, provide insights on large scales (several $R_{\mathrm{500}}$), but they reveal notable discrepancies that can be traced to their different AGN feedback implementations. We confront this picture by using state-of-the-art eROSITA X-ray data to study the properties of hot gas outside $R_{\mathrm{500}}$ of an X-ray selected sample of 25 galaxy groups, detected through their large-scale X-ray emission in eRASS1 and confirmed in the 2MRS spectroscopic catalogue. In doing so, we take into account, for the first time, the aperture-covariance effect between quantities with a shared integration radius. We put our results in context by comparing them to recent X-ray observations and numerical simulations with various AGN feedback recipes. We find a gas fraction at the median mass of the sample $M_{\mathrm{500}} = 2.5 \times 10^{13}M_{\odot}$ of $4.5 \pm 0.42 \%$. Similarly, at $R_{\mathrm{200c}}$ and the median mass $M_{\mathrm{200}} = 3.8 \times 10^{13}M_{\odot}$, we get a sub-cosmic $f_{\mathrm{gas,200}}$ of $6.1 \pm 0.7 \%$. Our $f_{\mathrm{gas}}−M$ relation comes in excellent agreement with the predictions of BAHAMAS, SIMBA, and the fiducial FLAMINGO simulation runs, while our $f_{\mathrm{gas}} − M$ and $L_{\mathrm{X}} − M$ relations deviate significantly from the predictions of the strong feedback simulation variations. Our work fills an important gap in our knowledge of low-mass galaxy groups and demonstrates the strengths of using eROSITA in tracing the hot gas budget with large-scale X-ray emission outside the virial regions.