Image Morphology of Misaligned Magnetically Arrested Disks

Abstract

Horizon scale images probe the plasma dynamics and spacetime in the vicinity of accreting black holes. Interpreting these images requires models that connect image morphology to the structure of the underlying accretion flow. Disk misalignment is expected in many systems, yet most horizon scale image analyses assume that the emitting flow is aligned with the black hole spin. We investigate whether tilted accretion flows produce image features distinguishable from axisymmetric flows and whether their effects can be absorbed by changes in aligned model parameters. Using general relativistic magnetohydrodynamic simulations of tilted magnetically arrested disks spanning black hole spins $a^*=-0.9375$ to $0.9375$ and initial disk tilts $0^\circ$ to $30^\circ$, we generate synthetic images and quantify their morphology through fits to an aligned, semi-analytic emission model. Using this approach, we show that high spin prograde models show little sensitivity to disk tilt, as the inner emitting flow aligns with the black hole spin. In contrast, retrograde tilted disks develop warped, non-axisymmetric inner structure that distorts the inner shadow and strongly alters image morphology. While the aligned semi-analytic model reproduces most prograde images well, retrograde tilted disk images are fit less accurately and yield biased inferred parameters, especially for spin. The image morphologies indicate that tilt affects horizon scale images only when misalignment survives into the near horizon emitting region, motivating image models that include disk tilt as an explicit degree of freedom when alignment is uncertain.