Polarization images of accretion flow around supermassive black holes:
  imprints of toroidal field structure
  With unprecedented angular resolution, the Event Horizon Telescope (EHT) has
opened a new era of black holes. We have previously calculated the expected
polarization images of M87* with the EHT observations in mind. There, we
demonstrated that circular polarization (CP) images, as well as the linear
polarization (LP) maps, can convey quite useful information to us, such as the
flow structure and magnetic field configuration around the black hole. In this
paper, we make new predictions for the cases in which disk emission dominates
over jet emission, bearing Sgr A* in mind. Here we set the proton-to-electron
temperature ratio of the disk component to be Tp/Te $\sim$ 2 so as to suppress
jet emission relative to emission from accretion flow. As a result, we obtain
ring-like images and triple-forked images around the black hole for face-on and
edge-on cases, respectively. We also find significant CP components in the
images ($\gtrsim 10\%$ in fraction), both with positive and negative signs,
amplified through the Faraday conversion, not sensitively depending on the
inclination angles. Furthermore, we find a "separatrix" in the CP images,
across which the sign of CP is reversed and on which the LP flux is brightest,
that can be attributed to the helical magnetic field structure in the disk.
These results indicate that future full polarization EHT images are a quite
useful tracer of the magnetic field structure. We also discuss to what extent
we will be able to extract information regarding the magnetic field
configurations, under the scattering in the interstellar plasma, in future EHT
polarimetric observations of Sgr A*.
