Temperature asymmetry in the Milky Way's hot circumgalactic medium induced by the Magellanic Clouds

Abstract

The Milky Way is surrounded by a hot diffuse circumgalactic medium (CGM) with temperatures of millions of degrees. Recent X-ray observations with the eROSITA satellite discovered a significant temperature asymmetry of this hot CGM, with the southern hemisphere being on average hotter than the northern one by a relative difference of ${\Delta} T/T \approx 12\%$, where $T$ is averaged over the entire CGM. In this Letter, we investigate whether the passage of the Magellanic Clouds can be responsible for this asymmetry by means of a hydrodynamical/N-body simulation. In the simulation, the Magellanic Clouds induce a relative motion of the Milky Way's disc of up to 40 km/s. This motion leads to compression of the CGM gas in the southern hemisphere, resulting in an overall temperature increase in that region. We estimate a south-north temperature difference of ${\Delta} T/T \approx 13-20\%$, consistent with the observations. We find that this temperature asymmetry is a recent phenomenon that began ~100 Myr ago.