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Thermal and chemical properties of the eROSITA bubbles from Suzaku observations

Abstract

The X-ray bright bubbles at the Galactic Centre 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 supervirial temperatures. Furthermore, we demonstrate that temperatures of the virial and supervirial 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 postshock 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.

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Fig. 1: X-ray emission maps from our Suzaku survey of the Galactic bubbles and the surrounding halo regions.
Fig. 2: F-test probability map for the hot-component significance required over the standard three-component SDXB model for the Suzaku observations investigated in this work.
Fig. 3: Distribution of the emission measures and the temperatures of the warm-hot and the hot components of the X-ray emission.

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Data availability

The data presented in this paper are publicly available at the High Energy Astrophysics Science Archive Research Center (HEASARC) archive.

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Acknowledgements

This research has made use of data obtained from the Suzaku satellite, a collaborative mission between the space agencies of Japan (Japan Aerospace Exploration Agency (JAXA)) and the USA (National Aeronautics and Space Administration (NASA)). We are grateful to B. Ryden for her notes of the ‘Radiate Gas Dynamics’ graduate course at Ohio State. We gratefully acknowledge support through the NASA Astrophysics Data Analysis Program (ADAP) grants 80NSSC18K0419 to A.G. and NNX16AF49G to S.M.

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A.G. did the X-ray data analysis and wrote the text. S.M. contributed to the interpretation of the results and revised the manuscript. J.K. did the Suzaku data reduction and made the images. S.D. and Y.K. helped with the interpretation of the results. All the coauthors contributed to the discussion and commented on the manuscript.

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Correspondence to Anjali Gupta.

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Nature Astronomy thanks Kartick Sarkar, Masayoshi Nobukawa and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Tables 1 and 2 and Figs. 1 and 2.

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Gupta, A., Mathur, S., Kingsbury, J. et al. Thermal and chemical properties of the eROSITA bubbles from Suzaku observations. Nat Astron 7, 799–804 (2023). https://doi.org/10.1038/s41550-023-01963-5

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