# Evidence for a hot galactic halo around the Andromeda Galaxy using fast radio bursts

**Authors:** Reshma Anna-Thomas, Casey J. Law, Eric W. Koch, Alexa C. Gordon, Kritti Sharma, Benjamin F. Williams, Nickolas M. Pingel, Sarah Burke-Spolaor, Zhuo Chen, Jordan Stanley, Calvin Dear, Frank Verdi, J. Xavier Prochaska, Geoffrey C. Bower, Laura Chomiuk, Liam Connor, Paul B. Demorest, Anya Nugent, Fabian Walter  
**arXiv:** [2503.02947](https://arxiv.org/abs/2503.02947)  
**Date:** 2025-03-04  
**Summary page:** https://www.summarizepaper.com/en/paper/2503.02947v1/

## Key points

- Fast Radio Bursts (FRBs) are brief bursts of radio waves that offer insights into matter in distant galaxies
- Researchers used the realfast fast transient detection system to detect FRBs from the Andromeda Galaxy (M31)
- Analysis of FRBs like FRB 20230903A and FRB 20230506C helped understand M31's electron density distribution
- Calculations considered factors like dispersion from Milky Way, host galaxy, and intergalactic medium
- Estimated contributions from M31 for FRB 20230903A and FRB 20230506C with confidence level of 90%
- Modeling showed M31's halo could contribute to dispersion measure (DM) values with specific ranges
- Measured DM_M31,halo values aligned closely with predictions based on M31's halo profile
- Indirect evidence suggested a hot halo surrounding M31 due to insufficient ions from cool halo alone
- Speculation about potential intersection between line of sight of FRB 20230506C and a baryon bridge connecting M31 with Milky Way
- Study sheds light on extragalactic matter structure through analysis of FRBs from Andromeda Galaxy

## Summary

Fast Radio Bursts (FRBs) are brief bursts of radio waves that provide valuable insights into the composition and distribution of matter in distant galaxies. In a recent study, researchers utilized the realfast fast transient detection system at the Very Large Array to detect and pinpoint two FRBs originating from the Andromeda Galaxy (M31). By analyzing these FRBs, specifically FRB 20230903A and FRB 20230506C, researchers were able to gain a better understanding of M31's electron density distribution. Through careful calculations that accounted for various contributing factors such as dispersion from the Milky Way, the host galaxy, and intergalactic medium along the line of sight, researchers estimated that M31 alone likely contributed between 21-217 pc cm^-3 for FRB 20230903A and between 43-338 pc cm^-3 for FRB 20230506C with a confidence level of 90%. Additionally, by modeling the contribution of M31's disk to the dispersion measure (DM), researchers determined that M31's halo could contribute between 9-145 pc cm^-3 for FRB 20230903A and between 28-286 pc cm^-3 for FRB 20230506C with a confidence level of 90%. Interestingly, the measured values of DM_M31,halo aligned closely with predictions based on the modified Navarro-Frenk-White profile of M31's halo at specific impact parameters. Furthermore, it was noted that ions from M31's cool halo alone were insufficient to explain the calculated DM_M31,halo values, suggesting indirect evidence of a hot halo surrounding M31. Moreover, there was speculation regarding a potential intersection between the line of sight of FRB 20230506C and a hot baryon bridge connecting M31 with our own Milky Way galaxy. This finding hints at complex interactions between galaxies in close proximity. Overall, this study sheds light on the intricate structure and composition of extragalactic matter through the analysis of Fast Radio Bursts originating from Andromeda Galaxy. The detailed measurements and modeling techniques employed provide valuable insights into the nature of galactic halos and their impact on observed phenomena in distant galaxies.