ALMA Science Verification Data: Millimeter Continuum Polarimetry of the Bright Radio Quasar 3C 286

TL;DR

This paper reports the first full-polarization ALMA observations of quasar 3C 286 at 1.3 mm, revealing highly ordered magnetic fields and EVPA changes linked to core position, with additional detection of a submillimeter galaxy.

Contribution

It presents the first full-polarization ALMA data of a radio quasar, demonstrating magnetic field properties at millimeter wavelengths and their relation to jet structure.

Findings

Core fractional polarization is about 17%, higher than at centimeter wavelengths.

EVPA in the core is approximately 39°, increasing from centimeter to millimeter wavelengths.

Detected a likely submillimeter galaxy in the field of view.

Abstract

We present full-polarization observations of the compact, steep-spectrum radio quasar 3C~286 made with the ALMA at 1.3~mm. These are the first full-polarization ALMA observations, which were obtained in the framework of Science Verification. A bright core and a south-west component are detected in the total intensity image, similar to previous centimeter images. Polarized emission is also detected toward both components. The fractional polarization of the core is about 17\%, this is higher than the fractional polarization at centimeter wavelengths, suggesting that the magnetic field is even more ordered in the millimeter radio core than it is further downstream in the jet. The observed polarization position angle (or EVPA) in the core is $\sim$\,$39^{\circ}$, which confirms the trend that the EVPA slowly increases from centimeter to millimeter wavelengths. With the aid of multi-frequency VLBI observations, we argue that this EVPA change is associated with the frequency-dependent core position. We also report a serendipitous detection of a sub-mJy source in the field of view, which is likely to be a submillimeter galaxy.