Magnetically Regulated Disk Formation in the Inner 100 au Region of the Class 0 Young Stellar Object OMC-3/MMS 6 Resolved by JVLA and ALMA

Abstract

We have carried out polarization calibration for archival Jansky Very Large Array (JVLA) (∼9 mm) full polarization observations toward the Class 0 young stellar object (YSO) OMC-3/MMS 6 (also known as HOPS-87), and then compared the results with the archival Atacama Large Millimeter Array (ALMA) 1.2 mm observations. The resolved spectral indices show that the innermost ∼100 au region of OMC-3/MMS 6 is marginally optically thin (e.g., τ ≲ 1) at ∼9 mm wavelength, such that the JVLA observations can directly probe the linearly polarized emission from nonspherical dust. Assuming that the projected long axis of dust grains is aligned perpendicular to magnetic field ( B -field) lines, we propose that the overall B -field topology resembles an hourglass shape. The geometry of this system is consistent with a magnetically regulated dense (pseudo)disk, although this “hourglass” appears to be ∼40° inclined with respect to the previously reported outflow axis. In contrast, the inner ∼100 au region of this YSO is likely very optically thick (e.g., τ ≫ 1) at ∼1 mm wavelength. The electric field position angles resolved by JVLA and ALMA present ∼90° offsets on this region, which indicate that the dominant polarization mechanism at 1 mm wavelength is dichroic extinction. This is the second case where the (sub)millimeter dichroic extinction is demonstrated by the direct comparison between the JVLA and ALMA polarization observations.