Wind-Fed GRMHD Simulations of Sagittarius A*: Tilt and Alignment of Jets
and Accretion Discs, Electron Thermodynamics, and Multi-Scale Modeling of the
Rotation Measure
Wind-fed models offer a unique way to form predictive models of the accretion
flow surrounding Sagittarius A*. We present 3D, wind-fed MHD and GRMHD
simulations spanning the entire dynamic range of accretion from parsec scales
to the event horizon. We expand on previous work by including nonzero black
hole spin and dynamically evolved electron thermodynamics. Initial conditions
for these simulations are generated from simulations of the observed Wolf-Rayet
stellar winds in the Galactic Centre. The resulting flow tends to be highly
magnetized (β≈2) with an ∼r−1 density profile
independent of the strength of magnetic fields in the winds. Our simulations
reach the MAD state for some, but not all cases. In tilted flows, SANE jets
tend to align with the angular momentum of the gas at large scales, even if
that direction is perpendicular to the black hole spin axis. Conversely, MAD
jets tend to align with the black hole spin axis. The gas angular momentum
shows similar behavior: SANE flows tend to only partially align while MAD flows
tend to fully align. With a limited number of dynamical free parameters, our
models can produce accretion rates, 230 GHz flux, and unresolved linear
polarization fractions roughly consistent with observations for several choices
of electron heating fraction. Absent another source of large-scale magnetic
field, winds with a higher degree of magnetization (e.g., where the magnetic
pressure is 1/100 of the ram pressure in the winds) may be required to get a
sufficiently large RM with consistent sign.Comment: Accepted by MNRAS. Animations for several figures in the paper are
available at
https://www.youtube.com/playlist?list=PL3pLmTeUPcqSd4jVBnRubYQpa-Dma25i