Unveiling Inner Shadows and Polarization Signatures of Rotating Einstein–Gauss–Bonnet Black Holes

Abstract Based on the backward ray-tracing method, we investigate the intensity and polarization images of a rotating Einstein–Gauss–Bonnet (EGB) black hole surrounded by a thin accretion disk. We examine the effects of the GB parameter $\xi$, the spin parameter $a$, and the observer inclination on the horizon-scale image of black hole. Our results show that $\xi$ mainly affects the size of the inner shadow, while the spin parameter controls its deformation. The photon-ring morphology is more sensitive to the viewing inclination than to the GB coupling. For polarized emission, the polarized-intensity distribution is consistent with the total-intensity distribution of the thin-disk image, but the polarization direction near the inner shadow and photon-ring regions responds clearly to changes in $\xi$. Finally, we conclude that, compared to previous reliance on either accretion disk or polarization images alone, the simultaneous combination and synergistic analysis of both can more profoundly reveal the optical properties of rotating EGB black holes, providing a stronger theoretical basis for identifying such black holes through future high-resolution observations.