First NIR Polarimetry of 30 Doradus

Abstract

Abstract We have carried out the first near-infrared (NIR) polarimetric imaging observations of the central part (7$\rlap{.}^{\prime}$7 $\times$ 7$\rlap{.}^{\prime}$7 $\sim 110 {\rm\; pc} \times 110 {\rm\; pc}$) of 30 Doradus. The totals of 106, 131, and 34 sources have significant polarization degrees at $J, H$, and $K_{\rm s}$, respectively. The $E$-vectors toward 30 Dor were mapped with unprecedentedly high resolutions. As previously noticed by optical observations, there is an overall tendency for the $E$-vectors to be roughly aligned in the east-west direction. In addition, our observations reveal a more complex structure of their alignment. The position angles of the $E$-vectors are not uniform, but show a gradual spatial variation. It is plausible to assume that they trace the magnetic field toward 30 Dor. One of the expanding shells toward 30 Dor, Shell 5, is clearly enveloped by $E$-vectors. The expanding shell has probably swept the magnetic field together into the rim, while creating the curved structure. We obtained the ratios of polarization degree among the NIR wavelengths: $P_H / P_J = 0.76\pm0.02$ and $P_{K_{\rm s}} / P_H = 0.87\pm0.06$. These fit a power-law dependence of $P \propto \lambda^{-0.9}$.