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

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1 Citation (Scopus)


Context. SPT-CL J2106-5844 is among the most massive galaxy clusters at zâ€., >â€., 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 ∼400  kpc 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
JournalAstronomy and Astrophysics
Publication statusPublished - 2021 Jun 1

Bibliographical note

Funding Information:
Acknowledgements. We are grateful to the referee for the stimulating suggestions and comments. These provided valuable indications that helped us improve this manuscript. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2016.1.01175.S and ADS/JAO.ALMA#2017.1.01649.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory (JAO) is operated by ESO, AUI/NRAO and NAOJ. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The Australian SKA Pathfinder is part of the Australia Telescope National Facility which is managed by CSIRO. Operation of ASKAP is funded by the Australian Government with support from the National Collaborative Research Infrastructure Strategy. ASKAP uses the resources of the Pawsey Supercomputing Centre. Establishment of ASKAP, the Murchison Radioastronomy Observatory and the Pawsey Supercomputing Centre are initiatives of the Australian Government, with support from the Government of Western Australia and the Science and Industry Endowment Fund. We acknowledge the Wajarri Yamatji people as the traditional owners of the Observatory site. The POSSUM project has been made possible through funding from the Australian Research Council, the Natural Sciences and Engineering Research Council of Canada, the Canada Research Chairs Program, and the Canada Foundation for Innovation. The Dunlap Institute is funded through an endowment established by the David Dunlap family and the University of Toronto. Partial support for LR comes from US National Science Foundation grant AST 17-14205 to the University of Minnesota. MJJ acknowledges support from the National Research Foundation of Korea under the program nos. 2017R1A2B2004644 and 2017R1A4A1015178. JLW acknowledges the support of the Natural Sciences and Engineering Research Council of Canada (NSERC) through grant RGPIN-2015-05948, and of the Canada Research Chairs program. LDM is supported by the ERC-StG ‘ClustersXCosmo’ grant agreement 716762. He would like to personally thank Alexandro Saro and Andrea Biviano for the constructive suggestions, and Gabriella Di Gennaro for helping me getting my mind around radio haloes. The authors thank Ettore Carretti and Michał Michałowski for the useful comments, and the GOGREEN collaboration for fruitful discussions and for providing the spectroscopic redshifts for the cluster members. We additionally thank the Additional Representative Images for Legacy (ARI-L) project for making us aware of the rich ALMA and ACA archival data sets. The results presented in this paper were produced using the following python packages: NumPy (Harris et al. 2020), SciPy (Virtanen et al. 2020), Matplotlib (Hunter 2007), dynesty (Speagle 2020), Astropy (Astropy Collaboration 2018), APLpy (Robitaille & Bressert 2012; Robitaille 2019).

Publisher Copyright:
© ESO 2021.

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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