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arXiv · 2507.04913

First detection of Circular Polarization in radio continuum towards a Massive Protostar

A. G. Cheriyan·S. Vig·Nirupam Roy·Samir Mandal·C. Carrasco-González·A. Rodríguez-Kamenetzky·A. Pasetto
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Abstract

Polarization measurements provide strong constraints on magnetic fields in star-forming systems. While magnetic field estimates of a few kiloGauss (kG) have been obtained near the surface of low-mass protostars, there are no analogous measurements in the immediate vicinity of the surface of massive protostars. We report the measurement of radio continuum circular polarization (CP) towards a massive protostar IRAS 18162-2048 for the first time wielding Karl G. Jansky Very Large Array (VLA) observations. The fractional CP varies between $3-5\%$ across the observed frequency range of $4-6$ GHz. We consider multiple hypotheses for the production of CP and propose (i) gyrosynchrotron emission and (ii) Faraday conversion due to turbulence in the magnetic medium - both driven by mildly relativistic electrons as plausible mechanisms. We estimate, for the first time, a magnetic field $B\gtrsim20-35$ G close to the massive protostar. The Lorentz factor of the low energy electrons is estimated to be in the range $\gamma_{min}\sim5-7$ for gyrosynchrotron emission and $80-100$ for Faraday conversion from our observations. The magnetic field estimate can provide important constraints to the formation models of massive stars.

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A. G. Cheriyan, S. Vig, Nirupam Roy, Samir Mandal, C. Carrasco-González, A. Rodríguez-Kamenetzky, A. Pasetto. 2025-07-07. First detection of Circular Polarization in radio continuum towards a Massive Protostar. https://arxiv.org/abs/2507.04913

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