Thermal and chemical properties of the eROSITA bubbles from Suzaku observations

TL;DR

This study uses Suzaku observations to reveal that the eROSITA bubbles' shells are characterized by complex, two-temperature X-ray emission, indicating denser gas rather than hotter shock-heated material, and supports stellar feedback as their origin.

Contribution

It provides the first detailed two-temperature thermal model of the eROSITA bubble shells, challenging previous shock-based assumptions and favoring stellar feedback models.

Findings

Shells are best described by a two-temperature model.

Shells are denser, not hotter, than ambient medium.

Non-solar Ne/O and Mg/O ratios support stellar feedback origin.

Abstract

The X-ray bright bubbles at the Galactic Center provide an opportunity to understand the effects of feedback on galaxy evolution. The shells of the eROSITA bubbles show enhanced X-ray emission over the sky background. Previously, these shells were assumed to have a single temperature component and to trace the shock-heated lower-temperature halo gas. Using Suzaku observations, we show that the X-ray emission of the shells is more complex and best described by a two-temperature thermal model: one component close to the Galaxy's virial temperature and the other at super-virial temperatures. Furthermore, we demonstrate 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. This leads us to conclude that the eROSITA bubble shells are X-ray bright because they trace denser gas, not because they are hotter. Given that the pre- and post-shock temperatures are similar and the compression ratio of the shock is high, we rule out that the bubble shells trace adiabatic shocks, in contrast to what was assumed in previous studies. We also observe non-solar Ne/O and Mg/O ratios in the shells, favouring stellar feedback models for the formation of the bubbles and settling a long-standing debate on their origin.