Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 499, Issue 3, Pages 3178-3192Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/staa3031
Keywords
accretion, accretion discs; black hole physics; MHD; methods: numerical; stars: jets; galaxies: individual: (SgrA*)
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Funding
- Oak Ridge Leadership Computing Facility - DOE office of Science User Facility [DE-AC05-00OR22725]
- Calcul Quebec
- Compute Canada
- Netherlands Organization for Scientific Research (NWO) VICI grant [639.043.513]
- Leverhulme Trust Early Career Research Fellowship
- NWO Spinoza Prize
- Northwestern University
- National Science Foundation [AST-1815304, AST-1911080]
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The candidate supermassive black hole in the Galactic Centre, Sagittarius A* (Sgr A*), is known to be fed by a radiatively inefficient accretion flow (RIAF), inferred by its low accretion rate. Consequently, radiative cooling has in general been overlooked in the study of Sgr A*. However, the radiative properties of the plasma in RIAFs are poorly understood. In this work, using full 3D general-relativistic magnetohydrodynamical simulations, we study the impact of radiative cooling on the dynamical evolution of the accreting plasma, presenting spectral energy distributions and synthetic sub-millimetre images generated from the accretion flow around Sgr A*. These simulations solve the approximated equations for radiative cooling processes self-consistently, including synchrotron, bremsstrahlung, and inverse Compton processes. We find that radiative cooling plays an increasingly important role in the dynamics of the accretion flow as the accretion rate increases: the mid-plane density grows and the infalling gas is less turbulent as cooling becomes stronger. The changes in the dynamical evolution become important when the accretion rate is larger than 10(-8) M-circle dot yr(-1) (greater than or similar to 10(-7)M(Edd), where M-Edd is the Eddington accretion rate). The resulting spectra in the cooled models also differ from those in the non-cooled models: the overall flux, including the peak values at the sub-mm and the far-UV, is slightly lower as a consequence of a decrease in the electron temperature. Our results suggest that radiative cooling should be carefully taken into account in modelling Sgr A* and other low-luminosity active galactic nuclei that have a mass accretion rate of M > 10(-7) M-Edd.
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