Abstract
Aims. Although from a theoretical point of view magnetic fields are believed to play a significant role during the early stages of star formation, especially during the main accretion phase, the magnetic field strength and topology is poorly constrained in the youngest accreting Class 0 protostars that lead to the formation of solar-type stars.Methods. We carried out observations of the polarized dust continuum emission with the SMA interferometer at 0.87 mm to probe the structure of the magnetic field in a sample of 12 low-mass Class 0 envelopes in nearby clouds, including both single protostars and multiple systems. Our SMA observations probed the envelope emission at scales ~600 − 5000 au with a spatial resolution ranging from 600 to 1500 au depending on the source distance.Results. We report the detection of linearly polarized dust continuum emission in all of our targets with average polarization fractions ranging from 2% to 10% in these protostellar envelopes. The polarization fraction decreases with the continuum flux density, which translates into a decrease with the H2column density within an individual envelope. Our analysis show that the envelope-scale magnetic field is preferentially observed either aligned or perpendicular to the outflow direction. Interestingly, our results suggest for the first time a relation between the orientation of the magnetic field and the rotational energy of envelopes, with a larger occurrence of misalignment in sources in which strong rotational motions are detected at hundreds to thousands of au scales. We also show that the best agreement between the magnetic field and outflow orientation is found in sources showing no small-scale multiplicity and no large disks at ~100 au scales.
Highlights
Understanding the physical processes at work during the earliest phase of star formation is key to characterize the typical outcome of the star formation process, put constraints on the efficiency of accretion and ejection mechanisms, and determine the pristine properties of planet-forming material
(i) By comparing the 0.87 mm Submillimeter Array (SMA) continuum fluxes with single-dish observations, we find that our interferometric observations recover
The low flux fractions contained in the compact component are consistent with the classification as Class 0 of our sources. (ii) We report the detection of linearly polarized dust emission in all the objects of the sample with mean polarization fractions ranging from 2% to 10%. (iii) We find a decrease of the polarization fraction with the estimated H2 column density
Summary
Understanding the physical processes at work during the earliest phase of star formation is key to characterize the typical outcome of the star formation process, put constraints on the efficiency of accretion and ejection mechanisms, and determine the pristine properties of planet-forming material. Class 0 objects are the youngest accreting protostars Andre et al 1993, 2000 The bulk of their mass resides in a dense envelope that is being actively accreted onto the central protostellar embryo during a short main accretion phase (t < 105 yr; Maury et al 2011; Evans et al 2009). Few polarization observations have been performed to characterize the magnetic field topology at the protostellar envelope scales where the angular momentum problem is relevant. We analyze observations of the 0.87 mm polarized dust continuum for a sample of 12 Class 0 (single and multiple systems) protostars with the SMA interferometer (Ho et al 2004) to increase the current statistics on the polarized dust continuum emission detected in protostellar envelopes on 750–2000 au scales. We used an iterative procedure to self-calibrate the Stokes I visibility data
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