SKA-Athena Synergy White Paper SKA-Athena Synergy Team July 2018. Edited by: Francisco J. Carrera and Silvia Martínez-Núñez on behalf of the Athena Community Office. Revisions provided by: Judith Croston, Andrew C. Fabian, Robert Laing, Didier Barret, Robert Braun, Kirpal Nandra Authorship Authors Rossella Cassano (INAF-Istituto di Radioastronomia, Italy). • Rob Fender (University of Oxford, United Kingdom). • Chiara Ferrari (Observatoire de la Côte d’Azur, France). • Andrea Merloni (Max-Planck Institute for Extraterrestrial Physics, Germany). • Contributors Takuya Akahori (Kagoshima University, Japan). • Hiroki Akamatsu (SRON Netherlands Institute for Space Research, The Netherlands). • Yago Ascasibar (Universidad Autónoma de Madrid, Spain). • David Ballantyne (Georgia Institute of Technology, United States). • Gianfranco Brunetti (INAF-Istituto di Radioastronomia, Italy) and Maxim Markevitch (NASA-Goddard • Space Flight Center, United States). Judith Croston (The Open University, United Kingdom). • Imma Donnarumma (Agenzia Spaziale Italiana, Italy) and E. M. Rossi (Leiden Observatory, The • Netherlands). Robert Ferdman (University of East Anglia, United Kingdom) on behalf of the SKA Pulsar Science • Working Group. Luigina Feretti (INAF-Istituto di Radioastronomia, Italy) and Federica Govoni (INAF Osservatorio • Astronomico,Italy). Jan Forbrich (University of Hertfordshire, United Kingdom). • Giancarlo Ghirlanda (INAF-Osservatorio Astronomico di Brera and University Milano Bicocca, Italy). • Adriano Ingallinera (INAF-Osservatorio Astrofisico di Catania, Italy). • Andrei Mesinger (Scuola Normale Superiore, Italy). • Vanessa Moss and Elaine Sadler (Sydney Institute for Astronomy/CAASTRO and University of Sydney, • Australia). Fabrizio Nicastro (Osservatorio Astronomico di Roma,Italy), Edvige Corbelli (INAF-Osservatorio As- • trofisico di Arcetri, Italy) and Luigi Piro (INAF, Istituto di Astrofisica e Planetologia Spaziali, Italy). Paolo Padovani (European Southern Observatory, Germany). • Francesca Panessa (INAF/Istituto di Astrofisica e Planetologia Spaziali, Italy). • Gabriele Ponti (Max-Planck Institute for Extraterrestrial Physics, Germany). • Gabriel Pratt (IRFU and Universitè Paris Diderot, France) and Melanie Johnston-Hollitt (School of • Chemical and Physical Sciences, New Zealand). Reinout van Weeren (Leiden Observatory, Leiden University, the Netherlands). • Manami Sasaki (Dr. Karl Remeis Observatory, Erlangen Centre for Astroparticle Physics, Friedrich- • Alexander-University Erlangen-Nürnberg, Germany). Roberto Soria (ICRAR-Curtin University, Australia and NAOC, Chinese Academy of Sciences, China). • Ian Stevens (University of Birmingham, United Kingdom). • Franco Vazza (Università di Bologna, Italy and Universität Hamburg, Germany), Stefano Ettori (INAF • Osservatorio Astronomico di Bologna, Italy) and C. Gheller (CSCS-ETHZ, Switzerland). Natalie Webb (Institut de Recherche en Astrophysique et Planétologie, France). • Contents 1 Cosmic dawn . 9 1.1 The epoch of reionization . 9 1.1.1 Introduction . 9 1.1.2 Did galaxies or AGN drive reionization? When does the transition occur? . 10 1.1.3 What is the large-scale environment of high-z AGN? . 11 1.1.4 Which source(s) of X-rays drove the epoch of heating in the early Universe? . 11 1.2 The first stars . 11 1.2.1 Introduction: Population III Stars . 11 1.2.2 Athena and SKA: revealing GRB-PopIII progenitors . 12 2 Evolution of black holes and galaxies . 13 2.1 Introduction . 13 2.1.1 X-ray background and the associated radio sources: key to AGN evolution . 13 2.2 Athena and the faint radio sky . 16 2.3 A multi-wavelength view of star formation in galaxies . 18 2.3.1 Introduction . 18 2.3.2 The key role of Athena and SKA . 19 2.4 The gas content of distant active galaxies with SKA and Athena . 20 2.4.1 Introduction . 20 2.4.2 Connecting neutral hydrogen and soft X-ray absorption in AGN . 21 3 Active galaxy feedback in galaxy clusters . 23 3.1 Introduction . 23 3.2 The impact of jets on the thermodynamic evolution of the ICM . 23 3.3 Inverse Compton X-ray emission of radio lobes . 25 3.3.1 Tracing the contribution of AGN magnetic fields and relativistic particle injection to the ICM . 25 3.3.2 Inverse Compton emission from radio galaxies: an important component of the X-ray sky . 27 3.4 Finding the earliest galaxy groups and clusters efficiently with radio surveys . 27 4 Non-thermal phenomena in galaxy clusters . 29 4.1 Introduction . 29 4.2 Giant radio halos and the physics of the ICM . 30 4.2.1 Turbulence and radio halos . 31 4.2.2 Collective plasma effects and ICM microphysics . 31 4.2.3 Statistical investigation of radio halos . 32 4.2.4 The case of radio mini-halos . 34 4.3 Giant radio relics and shocks in the ICM . 35 4.3.1 SKA-Athena synergy for the study of giant radio relics . 36 4.4 Magnetic fields in galaxy clusters . 37 4.4.1 SKA-Athena synergies . 38 5 Detecting the cosmic web . 41 5.1 Introduction . 41 5.2 Continuum emission from the cosmic web . 41 5.2.1 Detecting the WHIM through its shocked gas . 41 5.2.2 Detecting the WHIM through Faraday rotation . 43 5.3 The WHIM and the “roaming” baryons . 44 6 Black-hole accretion physics and astrophysical transients . 47 6.1 Introduction . 47 6.2 X-ray binary winds and jets . 47 6.3 X-ray binaries at the highest accretion rates . 49 6.4 Ultraluminous X-ray sources . 51 6.5 Tidal disruption events . 53 6.5.1 The role of X-rays and future radio surveys . 53 6.5.2 The role of Athena in studying jetted TDE . 54 7 Galactic astronomy: stars, planets, pulsars and supernovae . 57 7.1 Introduction . 57 7.2 Young stellar objects and dwarf stars . 57 7.2.1 Low-mass protostars . 57 7.2.2 Ultracool dwarfs . 57 7.2.3 SKA–Athena synergies . 58 7.3 Stars and star-planet interactions . 58 7.4 Massive stars . 59 7.4.1 X-ray/radio emission processes and characteristics . 59 7.4.2 SKA-Athena synergies . 60 7.5 Pulsars . 61 7.6 Supernova remnants . 62 7.6.1 Studying interstellar shocks with SKA and Athena . 63 References . 66 Acronym List . ..