Paradigm shift in understanding the Galactic eROSITA Bubbles

Abstract

The magnificent bubbles at the Galactic center provide a great channel to understand the effects of feedback on galaxy evolution. The newly discovered eROSITA bubbles show enhanced X-ray emission from the shells around bubbles. Previous works assumed that the X-ray emitting gas in the shells has a single temperature component and that they trace the shock-heated lower-temperature Galactic halo gas. Here we show that the thermal structure of the eROSITA bubble shells is more complex. Using Suzaku observations we find with high confidence that the X-ray emission from the shells is best described by a two-temperature thermal model, one near Galaxy's virial temperature at ~0.2 keV and the other at super-virial temperatures ranging between kT = 0.4-1.1 keV. Furthermore, we show that temperatures of the virial and super-virial components are similar in the shells and in the ambient medium, although the emission measures are significantly higher in the shells. We argue that the X-ray bright eROSITA bubble shells are the signature of compressed isothermal radiative shocks. The age of the bubbles is constrained to 70-130 Myr. This expansion timescale, as well as the observed non-solar Ne/O and Mg/O ratios, favor the stellar feedback models for the formation of the Galactic bubbles, settling a long-standing debate on the origin of the Galactic bubbles.

Detection of a Supervirial Hot Component in the Milky Way Circumgalactic Medium Along Multiple Sight Lines by Using the Stacking Technique

“…The same was found by Das et al (2021) for Mrk 421, whose line of sight does not cross the bubbles. This is further confirmed by emission studies of the CGM, which have found a hot component coexistent with the virial phase toward directions away from the Galactic center (e.g., Bhattacharyya et al 2022;Bluem et al 2022;Gupta et al 2022).…”

“…However, our analysis is too limited to further explore this possibility. This result would be in contrast to the emission measure of the CGM hot and warm phases, which have been observed to vary by an order of magnitude in large and short scales (Das et al 2019;Gupta et al 2021Gupta et al , 2022Bhattacharyya et al 2022;Bluem et al 2022).…”