First ALMA Detection of a Galaxy Cluster Merger Shock
Abstract
We report on the first ALMA measurement of a galaxy cluster merger shock, observed at the location of a radio relic in the famous El Gordo galaxy cluster at redshift z 0.9. Located at about half the current age of the Universe, this is also the most distant example of a directly measured astrophysical shock. ALMA Band 3 was utilised to measure the Sunyaev-Zel'dovich (SZ) effect signature that confirms a small-scale change in pressure as expected from the passage of a shock in the intracluster medium. The results support a previous radio-based estimate of the shock Mach number and display similarities, and also some mild tensions, with the X-ray based results. Most importantly, these results show the potential of ALMA to detect galaxy cluster shocks, observations that will advance our knowledge of cluster formation, non-thermal particle acceleration and amplification of magnetic fields across the entire observable Universe where such relic shocks can be found.
- Publication:
-
The Messenger
- Pub Date:
- December 2016
- Bibcode:
- 2016Msngr.166...53B