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

¹ Max-Planck-Institut für Astrophysik (MPA), Karl-Schwarzschild-Strasse 1, Garching 85741, Germany
² Astronomy Unit, Department of Physics, University of Trieste, via Tiepolo 11, Trieste 34131, Italy
e-mail: luca.dimascolo@units.it
³ INAF – Osservatorio Astronomico di Trieste, via Tiepolo 11, Trieste 34131, Italy
⁴ IFPU – Institute for Fundamental Physics of the Universe, Via Beirut 2, 34014 Trieste, Italy
⁵ European Southern Observatory (ESO), Karl-Schwarzschild-Strasse 2, Garching 85748, Germany
⁶ School of Chemical and Physical Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand
⁷ Minnesota Institute for Astrophysics, School of Physics and Astronomy, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455, USA
⁸ Department of Astronomy, Yonsei University, 50 Yonsei-ro, Seoul 03722, Korea
⁹ Department of Physics, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA
¹⁰ Space Research Institute, Profsoyuznaya str. 84/32, Moscow 117997, Russia
¹¹ The Inter-University Institute for Data Intensive Astronomy (IDIA), Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
¹² School of Science, Western Sydney University, Locked Bag 1797, Penrith, NSW 2751, Australia
¹³ Instituto de Física de Cantabria (CSIC-UC), Avda. Los Castros s/n, 39005 Santander, Spain
¹⁴ Australian Astronomical Optics, Macquarie University, 105 Delhi Rd, North Ryde, NSW 2113, Australia
¹⁵ Australia Telescope National Facility, CSIRO Astronomy and Space Science, PO Box 76, Epping, NSW 1710, Australia
¹⁶ National Radio Astronomy Observatory, PO Box O, Socorro, NM 87801, USA
¹⁷ Dunlap Institute for Astronomy and Astrophysics University of Toronto, Toronto, ON M5S 3H4, Canada

Received: 28 December 2020
Accepted: 12 April 2021

Abstract

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 ∼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.