# X-ray bubbles in the circumgalactic medium of TNG50 Milky Way- and M31-like galaxies: signposts of supermassive black hole activity

**Authors:** Annalisa Pillepich, Dylan Nelson, Nhut Truong, Rainer Weinberger, Ignacio Martin-Navarro, Volker Springel, Sandy M. Faber, Lars Hernquist  
**arXiv:** [2105.08062](https://arxiv.org/abs/2105.08062)  
**Date:** 2021-05-17  
**Summary page:** https://www.summarizepaper.com/en/paper/2105.08062v1/

## Key points

- Recent numerical simulations have attempted to reproduce the observed properties of X-ray emitting bubbles, shells, and cavities in the circumgalactic gas above and below the stellar disks of Milky Way- and Andromeda-like galaxies.
- A new study has analyzed the output of the TNG50 simulation - a gravity and magnetohydrodynamical run of a cosmological volume that models the formation and evolution of thousands of galaxies in the full cosmological context.
- The simulation returns bubbles and shells of over-pressurized gas above and below the disks of simulated galaxies with morphological features reminiscent of those observed in our own Milky Way galaxy.
- Two-thirds of the 198 Milky Way/M31 analogues simulated within TNG50 show one or more large-scale coherent features impinging into their gaseous halo. Some galaxies include a succession of bubbles or shells ranging from a few to many tens of kpc in height.
- The bubble gas is typically at temperatures between 10^6.4-7.2 K and enriched to metallicities between 0.5-2 solar.
- According to TNG50's results, X-ray emitting bubbles similar to those observed in the Milky Way should be a frequent feature of disk-like galaxies prior to, or on the verge of being quenched; this suggests that these bubbles should be within reach for eROSITA with only a few ks observations within our local Universe.

## Summary

Recent numerical simulations have attempted to reproduce the observed properties of X-ray emitting bubbles, shells, and cavities in the circumgalactic gas above and below the stellar disks of Milky Way- and Andromeda-like galaxies. A new study has analyzed the output of the TNG50 simulation - a gravity and magnetohydrodynamical run of a cosmological volume that models the formation and evolution of thousands of galaxies in the full cosmological context. The simulation returns bubbles and shells of over-pressurized gas above and below the disks of simulated galaxies with morphological features reminiscent of those observed in our own Milky Way galaxy. These bubbles are a manifestation of episodic kinetic energy injections from supermassive black holes at galaxy centers that accrete at low Eddington ratios. Two-thirds of the 198 Milky Way/M31 analogues simulated within TNG50 show one or more large-scale coherent features impinging into their gaseous halo. Some galaxies include a succession of bubbles or shells ranging from a few to many tens of kpc in height. These are prominent in gas pressure, X-ray emission, gas temperature, often exhibiting sharp boundaries indicative shocks with typical Mach numbers ranging from 2-4. The bubble gas is typically at temperatures between 10^6.4-7.2 K and enriched to metallicities between 0.5-2 solar. The bubbles expand with speeds as high as 1000-2000 km/s (about 1-2 kpc/Myr), but with great diversity and larger bubbles expanding at slower speeds. According to TNG50's results, X-ray emitting bubbles similar to those observed in the Milky Way should be a frequent feature of disk-like galaxies prior to, or on the verge of being quenched; this suggests that these bubbles should be within reach for eROSITA with only a few ks observations within our local Universe.