ALMA's Polarized View of 10 Protostars in the Perseus Molecular Cloud

TL;DR

This study uses ALMA 870 μm dust polarization observations to analyze the polarization signatures of 10 protostars in the Perseus Molecular Cloud, revealing different polarization mechanisms at disk and envelope scales.

Contribution

It provides detailed polarization observations of multiple protostars, distinguishing polarization mechanisms at different scales and identifying signatures of dust scattering and magnetic alignment.

Findings

Disk candidates show polarization vectors along the minor axis, indicating dust scattering.

Envelope polarization is higher and more disordered, likely due to magnetic alignment.

Polarization distributions differ significantly between disk and envelope scales.

Abstract

We present 870 $\mu$m ALMA dust polarization observations of 10 young Class 0/I protostars in the Perseus Molecular Cloud. At $\sim$ 0.35$"$ (80 au) resolution, all of our sources show some degree of polarization, with most (9/10) showing significantly extended emission in the polarized continuum. Each source has incredibly intricate polarization signatures. In particular, all three disk-candidates have polarization vectors roughly along the minor axis, which is indicative of polarization produced by dust scattering. On $\sim$ 100 au scales, the polarization is at a relatively low level ($\lesssim 1\%$) and is quite ordered. In sources with significant envelope emission, the envelope is typically polarized at a much higher ($\gtrsim 5\%$) level and has a far more disordered morphology. We compute the cumulative probability distributions for both the small (disk-scale) and large (envelope-scale) polarization percentage. We find that the two are intrinsically different, even after accounting for the different detection thresholds in the high/low surface brightness regions. We perform Kolmogorov-Smirnov and Anderson-Darling tests on the distributions of angle offsets of the polarization from the outflow axis. We find disk-candidate sources are different from the non-disk-candidate sources. We conclude that the polarization on the 100 au scale is consistent with the signature of dust scattering for disk-candidates and that the polarization on the envelope-scale in all sources may come from another mechanism, most likely magnetically aligned grains.