A Magnetic Field Connecting the Galactic Center Circumnuclear Disk with Streamers and Mini-spiral -Implications from 850 $\mu$m Polarization Data

Abstract

Utilizing James Clark Maxwell Telescope (JCMT) 850 $\mu$m SCUPOL dust polarization data, we investigate the configuration of the magnetic ($B$) field in the circumnuclear disk (CND) of the Galactic Center (GC). The SCUPOL data show a highly improved polarization coverage and resolution compared to earlier 100 $\mu$m observations. The 850 $\mu$m data have a resolution and coverage similar to previous 350 $\mu$m polarimetry data. However, with a proper sampling on a 10$"$ grid, we find the 850 $\mu$m data trace the morphological structures of the CND substantially better. Furthermore, because the 850 $\mu$m trace the field deeper into the material near Sgr A*, they represent the highest resolution submillimeter probe to date of the CND magnetic field. The observed $B$-field morphology is well described by a self-similar axisymmetric disk model where the radial infall velocity is one quarter of the rotational velocity. A detailed comparison with higher-resolution interferometric maps from the Submillimeter Array further reveals that the $B$-field aligns with the neutral gas streamers connecting to the CND. Moreover, the innermost observed $B$-field structure also appears to trace and align with the mini-spiral located inside the CND. This suggests that there is one underlying $B$-field structure that is connecting the CND with its streamers and the inner mini-spiral. An estimate of $\beta_{\rm Plasma} \lesssim 1-$based on the global B-field morphology that constrains the azimuthal-to-vertical field strength ratio of around 40 combined with a measurement of the azimuthal velocity--indicates that the B-field appears dynamically significant towards the CND and also onwards to the inner mini-spiral.