eROSITA cosmology with galaxy groups: Hot gas budget out to the virial radius

Non-gravitational processes that expel hot gas beyond the virial regions of groups and clusters of galaxies, known collectively as baryonic feedback, play a key role in reshaping the matter distribution of the Universe on Mpc scales. We use eROSITA observations of a complete sample of 25 galaxy groups selected from the first public release of the eROSITA-DE data (eRASS1) and identified with the Two Micron Redshift Survey optical group catalogue (2MRS). We extract and fit surface brightness (SBx) profiles and present hot gas mass and hot gas fraction profiles out to R 200. We perform a Bayesian analysis of M gas-M tot, L X-M tot, and L X-M gas relations, taking into account the aperture covariance effects. At R 500, we report uniformly flat SBx profiles with a mean β parameter of 0.38 plus or minus0.04, steepening to β= 0.76 plus or minus0.19 beyond R 500. We measure a sub-cosmic hot gas fraction at the median mass of our sample M 500 = 2.54 times10 13M of f gas,500 = 4.32 plus or minus0.42%. Similarly, at R 200 and the median mass M 200 = 3.69 times10 13M, we obtain f gas,200=5.78 plus or minus0.69%. Our f gas-M tot and L X-M tot relations show significant deviations from the predictions of the strong feedback variants of the FLAMINGO simulation (2.5σ to 8.0σ tension), while fiducial FLAMINGO and BAHAMAS provide the closest match to our measurements. Using our measured baryon fractions and the SP(k) model, we infer a 10%-15% reduction in the matter power spectrum at k = 5 h Mpc-1 relative to a dark matter-only universe, in agreement with fiducial FLAMINGO and BAHAMAS, while revealing a growing tension on smaller scales with the strong feedback variants.