Impacts of radiative cooling on the images of a black hole shadow and extended jets in two-temperature GRMHD simulations

The recent 230 GHz observations from the Event Horizon Telescope (EHT) collaboration have successfully imaged the supermassive black hole shadow of the M87 galaxy. However, the relatively high radiative efficiency observed in the hot accretion flow suggests that radiative cooling is nonnegligible and should be considered when calculating the electron temperature. In this study, we compared accretion models without and with radiative cooling across a range of mass accretion rates, aiming to assess the impact of cooling on the disk structure, electron temperature distribution, black hole shadow morphology, broadband spectral energy distributions (SEDs), and flux variability. We performed general relativistic radiative transfer (GRRT) calculations on two-temperature, radiative, general relativistic magnetohydrodynamic simulations, employing different electron heating prescriptions across a range of mass accretion rates, dot M _ BH = (1. 0 - 10), _ 10^ -6 M Edd. Our models incorporate the nonthermal electron distribution function, analyzing the radiation transfer due to synchrotron emission at 230 GHz with a fixed viewing inclination angle of 163^̧irc. These simulations were targeted toward M87 *. By comparing density profiles, electron temperature distributions, GRRT images, SEDs, and time variability between models without and with radiative cooling across different mass accretion rates, we find that the radiative cooling sharply decreases the electron temperature in the inner disk around the equatorial plane (rłesssim 10, r_), where the density is highest. In contrast, the temperature in the jet sheath decreases slightly. Radiative cooling leads to a dimmer disk, more extended and brighter jets, and an overall reduction in total flux. For a given accretion rate, cooling reduces the high-frequency flux compared to models without radiative losses. We also find that the time variability mainly originates from the midplane region for both non-cooling and cooling cases. With increasing mass accretion rate, time variability decreases in both non-cooling and cooling cases. Although currently below the dynamic range of EHT observations, the features identified in this study can be resolved by next-generation arrays such as the ngEHT. g