Abstract
Abstract Utilizing James Clark Maxwell Telescope 850 μm SCUPOL dust polarization data, we investigate the configuration of the magnetic (B) field in the circumnuclear disk (CND) of the Galactic center. The SCUPOL data show a highly improved polarization coverage and resolution compared with earlier 100 μm observations. The 850 μm data have a resolution and coverage similar to previous 350 μm polarimetry data. However, with a proper sampling on a 10″ grid, we find that the 850 μm data trace the morphological structures of the CND substantially better. Furthermore, because the 850 μm trace the field deeper into the material near SgrA*, 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 β Plasma ≲ 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 toward the CND and also onwards to the inner mini-spiral.
Highlights
Utilizing James Clark Maxwell Telescope (JCMT) 850 μm SCUPOL dust polarization data, we investigate the configuration of the magnetic (B) field in the circumnuclear disk (CND) of the Galactic Center (GC)
As already hinted by the earlier lower-resolution 100 μm polarization data (Hildebrand et al 1990, 1993), the B-field of the CND traced by the higher-resolution 850 μm SCUPOL data at a 20′′ resolution can be described as an axially symmetric field, which is generated by the differentially-rotating radial inflow in the WKmodel
We find that the northeast lobe (NE-lobe) and the region E can be better fitted by the model gc4
Summary
The origin of the 2-pc circumnuclear disk (CND) in the Galactic Center (GC) has remained unclear in spite of intensive studies over the past decades (e.g., Gusten et al 1987; Jackson et al 1993; Amo-Baladron et al 2011; Harris et al 1985; Mezger et al 1989; Etxaluze et al 2011; Lau et al 2013; Dent et al 1993; Morris & Serabyn 1996; Wright et al 2001; Montero-Castano et al 2009; Martın et al 2012; Herrnstein & Ho 2002, 2005; Christopher et al 2005; Requena-Torres et al 2012; Mills et al 2013; Hsieh et al 2017). Near-infrared polarimetric data have shown that the orientation of the B-field is more parallel to the Galactic plane (toroidal), but is nearly perpendicular to the plane above b ≥ 0.4◦ (Nishiyama et al 2010) This provides evidence for a smooth transition of the large-scale Bfield. Wardle & Konigl (1990); Desch & Roberge (1997) investigated a smooth disk model for the CND including the B-field They adopted an axially symmetric magnetic model where an initially poloidal field threading the differentially rotating disk is pulled into a toroidal configuration. This alignment of field orientations with the Galactic plane is attributed to a large-scale toroidal B-field configuration (i.e., azimuthal field). In order to work with the maximum of independent data points, we present data with σP ≥ 2, and we will focus on the B-field structure of the CND
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