Spiral Magnetic Field and Their Role on Accretion Dynamics in the Circumnuclear Disk of Sagittarius A*: Insight from {\lambda} = 850 {\mu}m Polarization Imaging

Abstract

We showcase a study on the physical properties of the Circumnuclear Disk surrounding the Sgr A* of the Galactic Center, emphasizing the role of magnetic field (B field) with 0.47 pc spatial resolution, based on the sensitive {\lambda} = 850 {\mu}m polarization data taken with the JCMT. The B field within the CND exhibits a coherent spiral pattern. Applying the model described by Wardle and Ko\ddot{o}nigl 1990 (WK model) to the observed B field pattern, it favors gas-pressure-dominant models without dismissing a gas-and-B field comparable model, leading us to estimate the B-field strength in the ionized cavity around Sgr A* as 0.24 + 0.05 mG. Analysis -0.04 based on the WK model further allows us to derive representative B-field strengths for the radial, azimuthal, and vertical components as (Br,B{\phi},Bz) = (0.4 \pm 0.1,-0.7 \pm 0.2,0.2 \pm 0.05) mG, respectively. A key finding is that the |{\phi}| component is dominant over Br and Bz components, consistent with the spiral morphology, indicating that the CND' s B-field is predominantly toroidal, possibly shaped by accretion dynamics. Considering the turbulent pressure, estimated plasma \{beta} values indicate the effective gas pressure should surpass the magnetic pressure. Assessing the CND of our MWG in the toroidal-and-vertical stability parameter space, we propose that such an "effective" magnetoro-tational instability (MRI) may likely be active. The estimated maximum unstable wavelength, {\lambda}max = 0.1 \pm 0.1 pc, is smaller than the CND' s scale height (0.2 \pm 0.1 pc), which indicates the potential for the effective MRI intermittent cycles of \sim 10^{6} years, which should profoundly affect the CND's evolution, considering the estimated mass accretion rate of 10^{-2}M_{\odot} yr^{-1} to the Sgr A*.