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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 hasin general been overlooked in the study of Sgr A*. However, the radiativeproperties of the plasma in RIAFs are poorly understood. In this work, usingfull 3D general-relativistic magneto-hydrodynamical simulations, we study theimpact of radiative cooling on the dynamical evolution of the accreting plasma,presenting spectral energy distributions and synthetic sub-millimeter imagesgenerated from the accretion flow around Sgr A*. These simulations solve theapproximated equations for radiative cooling processes self-consistently,including synchrotron, bremsstrahlung, and inverse Compton processes. We findthat radiative cooling plays an increasingly important role in the dynamics ofthe accretion flow as the accretion rate increases: the mid-plane density growsand the infalling gas is less turbulent as cooling becomes stronger. Thechanges in the dynamical evolution become important when the accretion rate islarger than $10^{-8}\,M_{\odot}~{\rm yr}^{-1}$ ($\gtrsim 10^{-7} \dot{M}_{\rmEdd}$, where $\dot{M}_{\rm Edd}$ is the Eddington accretion rate). Theresulting spectra in the cooled models also differ from those in the non-cooledmodels: the overall flux, including the peak values at the sub-mm and thefar-UV, is slightly lower as a consequence of a decrease in the electrontemperature. Our results suggest that radiative cooling should be carefullytaken into account in modelling Sgr A* and other low-luminosity active galacticnuclei that have a mass accretion rate of $\dot{M} > 10^{-7}\,\dot{M}_{\rmEdd}$.

Spectral and Imaging properties of Sgr A* from High-Resolution 3D GRMHD Simulations with Radiative Cooling