Distortion of Magnetic Fields in a Starless Core. IV. Magnetic Field Scaling on Density and Mass-to-flux Ratio Distribution in FeSt 1-457

Kandori, Ryo; Tomisaka, Kohji; Tamura, Motohide; Saito, Masao; Kusakabe, Nobuhiko; Nakajima, Yasushi; Kwon, Jungmi; Nagayama, Takahiro; Nagata, Tetsuya; Tatematsu, Ken’ichi

In the present study, the magnetic field scaling on density, | B| \propto {ρ }κ , was revealed in a single starless core for the first time. The κ index of 0.78 ± 0.10 was obtained toward the starless dense core FeSt 1-457 based on the analysis of the radial distribution of the polarization angle dispersion of background stars measured at the near-infrared wavelengths. The result prefers κ = 2/3 for the case of isotropic contraction, and the difference of the observed value from κ = 1/2 is 2.8 sigma. The distribution of the ratio of mass-to-magnetic flux was evaluated. FeSt 1-457 was found to be magnetically supercritical near the center (λ ≈ 2), whereas nearly critical or slightly subcritical at the core boundary (λ ≈ 0.98). Ambipolar diffusion-regulated star formation models for the case of moderate magnetic field strength may explain the physical status of FeSt 1-457. The mass-to-flux ratio distribution for typical dense cores (critical Bonnor-Ebert sphere with central λ = 2 and κ = 1/2-2/3) was calculated, and found to be magnetically critical/subcritical at the core edge, which indicates that typical dense cores are embedded in and evolve from magnetically critical/subcritical diffuse surrounding medium.

DOI: 10.3847/1538-4357/aadb3f