Basu, K.K.BasuSommer, M.M.SommerErler, J.J.ErlerEckert, D.D.EckertVAZZA, FRANCOFRANCOVAZZAMagnelli, B.B.MagnelliBertoldi, F.F.BertoldiTOZZI, PaoloPaoloTOZZI2020-05-072020-05-0720162041-8205http://hdl.handle.net/20.500.12386/24595We present ALMA measurements of a merger shock using the thermal Sunyaev-Zel’dovich (SZ) effect signal, at the location of a radio relic in the famous El Gordo galaxy cluster at z≈ 0.9. Multi-wavelength analysis in combination with the archival Chandra data and a high-resolution radio image provides a consistent picture of the thermal and non-thermal signal variation across the shock front and helps to put robust constraints on the shock Mach number as well as the relic magnetic field. We employ a Bayesian analysis technique for modeling the SZ and X-ray data self-consistently, illustrating respective parameter degeneracies. Combined results indicate a shock with Mach number { M }={2.4}<SUB>-0.6</SUB><SUP>+1.3</SUP>, which in turn suggests a high value of the magnetic field (of the order of 4-10 μ {{G}}) to account for the observed relic width at 2 GHz. At roughly half the current age of the universe, this is the highest-redshift direct detection of a cluster shock to date, and one of the first instances of an ALMA-SZ observation in a galaxy cluster. It shows the tremendous potential for future ALMA-SZ observations to detect merger shocks and other cluster substructures out to the highest redshifts.STAMPAenArticle10.3847/2041-8205/829/2/L232-s2.0-84991111345000385412300002https://iopscience.iop.org/article/10.3847/2041-8205/829/2/L232016ApJ...829L..23BFIS/05 - ASTRONOMIA E ASTROFISICAScienze Fisiche Settori ERC (ERC) di riferimento::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation