Multiwavelength view of SPT-CL J2106-5844: The radio galaxies and the thermal and relativistic plasmas in a massive galaxy cluster merger at z ≃ 1.13

Luca Di Mascolo*, Tony Mroczkowski, Yvette Perrott, Lawrence Rudnick, M. James Jee, Kim Hyeonghan, Eugene Churazov, Jordan D. Collier, Jose M. Diego, Andrew M. Hopkins, Jinhyub Kim, Bärbel S. Koribalski, Joshua D. Marvil, Remco van der Burg, Jennifer L. West

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)
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Context. SPT-CL J2106-5844 is among the most massive galaxy clusters at z > 1 yet discovered. While initially used in cosmological tests to assess the compatibility with Λ Cold Dark Matter cosmology of such a massive virialized object at this redshift, more recent studies indicate SPT-CL J2106-5844 is undergoing a major merger and is not an isolated system with a singular, well-defined halo.

Aims. We use sensitive, high spatial resolution measurements from the Atacama Large Millimeter/Submillimeter Array (ALMA) and Atacama Compact Array (ACA) of the thermal Sunyaev-Zeldovich (SZ) effect to reconstruct the pressure distribution of the intracluster medium in this system. These measurements are coupled with radio observations from the pilot survey for the Evolutionary Map of the Universe, using the Australian Square Kilometre Array Pathfinder (ASKAP), and the Australia Telescope Compact Array (ATCA) to search for diffuse nonthermal emission. Further, to better constrain the thermodynamic structure of the cluster, we complement our analysis with reprocessed archival Chandra observations.

Methods. We jointly fit the ALMA and ACA SZ data in uv-space using a Bayesian forward modeling technique. The ASKAP and low-frequency ATCA data are processed and imaged to specifically highlight any potential diffuse radio emission.

Results. In the ALMA and ACA SZ data, we reliably identify at high significance two main gas components associated with the mass clumps inferred from weak lensing. Our statistical test excludes at the ∼9.9σ level the possibility of describing the system with a single SZ component. While the components had been more difficult to identify in the X-ray data alone, we find that the bimodal gas distribution is supported by the X-ray hardness distribution. The EMU radio observations reveal a diffuse radio structure ∼400kpc in projected extent along the northwest-southeast direction, indicative of strong activity from the active galactic nucleus within the brightest cluster galaxy. Interestingly, a putative optical star-forming filamentary structure detected in the HST image is in an excellent alignment with the radio structure, albeit on a smaller scale.

Original languageEnglish
Article numberA153
Pages (from-to)1-18
Number of pages18
JournalAstronomy and Astrophysics
Publication statusPublished - 24 Jun 2021

Bibliographical note

Reproduced with permission from Astronomy & Astrophysics, Copyright ESO 2021. First published in Astronomy and Astrophysics, 650, A153, 2021, published by EDP Sciences. The original publication is available at Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.


  • Cosmic background radiation
  • Galaxies: clusters: individual: SPT-CL J2106-5844
  • Galaxies: clusters: intracluster medium
  • Radio continuum: galaxies


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