Spatially resolved origin of millimeter-wave linear polarization in the nuclear region of 3C 84
Journal article, 2019

We report results from a deep polarization imaging of the nearby radio galaxy 3C 84 (NGC 1275). The source was observed with the Global Millimeter VLBI Array (GMVA) at 86 GHz at an ultrahigh angular resolution of 50 μas (corresponding to ∼200Rs). We also add complementary multiwavelength data from the Very Long Baseline Array (VLBA; 15 and 43 GHz) and from the Atacama Large Millimeter/submillimeter Array (ALMA; 97.5, 233.0 and 343.5 GHz). At 86 GHz, we measured a fractional linear polarization of ∼2% in the VLBI core region. The polarization morphology suggests that the emission is associated with an underlying limb-brightened jet. The fractional linear polarization is lower at 43 and 15 GHz (∼0.3-0.7% and <0.1%, respectively). This suggests an increasing linear polarization degree toward shorter wavelengths on VLBI scales. We also obtain a large rotation measure (RM) of ∼10 5-6 rad m 2 in the core at 43 GHz. Moreover, the VLBA 43 GHz observations show a variable RM in the VLBI core region during a small flare in 2015. Faraday depolarization and Faraday conversion in an inhomogeneous and mildly relativistic plasma could explain the observed linear polarization characteristics and the previously measured frequency dependence of the circular polarization. Our Faraday depolarization modeling suggests that the RM most likely originates from an external screen with a highly uniform RM distribution. To explain the large RM value, the uniform RM distribution and the RM variability, we suggest that the Faraday rotation is caused by a boundary layer in a transversely stratified jet. Based on the RM and the synchrotron spectrum of the core, we provide an estimate for the magnetic field strength and the electron density of the jet plasma.

Galaxies: jets

Galaxies: individual: NGC 1275

Techniques: polarimetric

Galaxies: active

Techniques: interferometric

Galaxies: individual: 3C 84

Author

J. Y. Kim

Max Planck Institute

T.P. Krichbaum

Max Planck Institute

A. Marscher

Boston University

S.G. Jorstad

Boston University

Saint Petersburg State University - Spsu

I. Agudo

CSIC - Instituto de Astrofísica de Andalucía (IAA)

C. Thum

Instituto de Radio Astronomía Millimétrica

J. Hodgson

Korea Astronomy and Space Science Institute

N. R. Macdonald

Max Planck Institute

Eduardo Ros

Max Planck Institute

R.S. Lu

Max Planck Institute

Shanghai Astronomical Observatory

M. Bremer

Institut de RadioAstronomie Millimetrique (IRAM)

P. de Vicente

Yebes Observatory

Michael Lindqvist

Chalmers, Space, Earth and Environment, Onsala Space Observatory, Onsala Space Observatory, Observation Support

S. Trippe

Seoul National University

A.J. Zensus

Max Planck Institute

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 622 1 A196

Subject Categories

Meteorology and Atmospheric Sciences

Astronomy, Astrophysics and Cosmology

Fusion, Plasma and Space Physics

DOI

10.1051/0004-6361/201832920

More information

Latest update

7/19/2019