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Modern galaxy evolution theories predict a large fraction of ordinary matter to be distributed in the form of gas over the largest galactic scales, with most of the gas mass encompassing the peak and high tail of the overall temperature distribution1. Satellite galaxies however, may lose a large amount of this extended gas due to stripping and ram pressure generated by their in-fall onto a larger system2. The presence of highly ionized gas associated with the Small and Large Magellanic Clouds has been recently confirmed through indirect probes3,4. Using eROSITA/SRG data, in this work we show the first direct images of the X-ray emission from the hottest gas associated to the circum-galactic medium surrounding the Magellanic Clouds. We discover an extended hot gas phase at ~2.3×106 K. This temperature challenges the theoretical expectations from a virialized system5,6 implying that heating mechanisms are at play in the Magellanic Clouds circum-galactic medium. We also discover a strong perturbation that we identify as a cold front in the (Galactic) South direction of the Magellanic Clouds, morphologically connected to them both. The cold front -the first ever discovered at galactic scales (~10 kpc)- also appears to be coincident with enhanced polarization at radio frequencies, as well as with a tangential alignment of the magnetic field lines. The detected discontinuity in the properties of the gas surrounding the Magellanic Clouds is consistent with a gas reservoir being perturbed by the three-body interaction between the Magellanic Clouds and the Milky Way7,8. The Magellanic Clouds provide a unique laboratory for assessing the presence of a hot gas phase in in-falling satellite systems9. The detection of a still large reservoir of hot gas, together with the detection of a front connected with thermal heating and magnetic amplification corroborates and inform galaxy evolution theories10.

The eROSITA X-ray telescope on board the Spectrum-Roentgen-Gamma (SRG) satellite has started to detect new X-ray sources over the full sky at an unprecedented rate. Understanding the performance and selection function of the source detection is important for the subsequent scientific analysis of the eROSITA catalogs. Through simulations, we test and optimize the eROSITA source detection procedures, and we characterize the detected catalog quantitatively. Taking the eROSITA Final Equatorial-Depth Survey (eFEDS) as an example, we ran extensive photon-event simulations based on our best knowledge of the instrument characteristics, the background spectrum, and the population of astronomical X-ray sources. We introduce a method of analyzing source detection completeness, purity, and efficiency based on the origin of each photon. According to the source detection efficiency measured in the simulation, we chose a two-pronged strategy to build eROSITA X-ray catalogs, creating a main catalog using only the most sensitive band (0.2-2.3 keV) and an independent hard-band-selected catalog using multiband detection in a range up to 5 keV. Because our mock data are highly representative of the real eFEDS data, we used the mock catalogs to measure the completeness and purity of the eFEDS catalogs as a function of multiple parameters, such as detection likelihood, flux, and luminosity. These measurements provide a basis for choosing the eFEDS catalog selection thresholds. The mock catalogs (available with this paper) can be used to construct the selection function of active galactic nuclei and galaxy clusters. A direct comparison of the output and input mock catalogs also gives rise to a correction curve that converts the raw point-source flux distribution into the intrinsic number counts distribution., Comment: Accepted by A&A for the Special Issue: The Early Data Release of eROSITA and Mikhail Pavlinsky ART-XC on the SRG Mission

We examine deep Chandra observations of the nearby Perseus and Centaurus galaxy clusters to examine AGN feedback and enrichment of the intracluster medium. We show evidence of 100 Myr of activity by the central nucleus in Perseus, generating shocks, bubbles and sound waves, heating the cluster core. Despite the AGN activity there exist 10 solar masses of ∼ 5× 10 K gas embedded in an intracluster medium 5 to 10 times hotter than it. Transport properties of the intracluster medium are likely to be important. We observe and map the distribution of metals in the Centaurus cluster, and show that Type II supernova enrichment is important in even the core of this cluster. It has been relatively undisturbed for 8 Gyr with a close heating/cooling balance.