First polarization study of the M87 jet and active galactic nuclei at submillimeter wavelengths with ALMA

Abstract

We present full-polarization observations at $\lambda =0.87$ mm (345 GHz) conducted with the Atacama Large Millimeter/submillimeter Array (ALMA) toward Messier 87 (M87) and seven other radio-loud active galactic nuclei (AGN). We determine polarization and Faraday properties of the targets, with linear polarization (LP) fractions spanning 1\% to 17\%, and Faraday rotation measures (RMs) exceeding $10^5$ rad m${}^{-2}$. These RM values, 1-2 orders of magnitude higher than typically observed at $\lambda >3$ mm, suggest denser Faraday screens or stronger magnetic fields in the (sub)millimeter emission regions. Additionally, we present the first submillimeter polarized images of the M87 jet and the observed AGN. In the M87 jet, we identify RM gradients and sign reversals, suggestive of a helical magnetic field structure extending over kiloparsec scales. These observations were part of the ALMA Band~7 Very Long Baseline Interferometry (VLBI) commissioning during the April 2021 Event Horizon Telescope (EHT) campaign. The results provide essential constraints for calibrating, analyzing, and interpreting VLBI data from the EHT at 345 GHz, representing a critical step toward submillimeter VLBI imaging.

17 pages, accepted for publication in A&A

References in corpus (23)

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• First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way
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• First M87 Event Horizon Telescope Results. II. Array and Instrumentation
• First M87 Event Horizon Telescope Results. III. Data Processing and Calibration
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• Probing the Parsec-scale Accretion Flow of 3C 84 with Millimeter Polarimetry
• Linear polarization in the nucleus of M87 at 7 mm and 1.3 cm
• Parsec Scale Faraday-Rotation Structure Across the Jets of 9 Active Galactic Nuclei
• First Very Long Baseline Interferometry Detections at 870μm
• A Characterization of the ALMA Phasing System at 345 GHz

Cited by in corpus (3)

• ALMA polarimetry of radio-quiet AGNs
• Constraints on High-Frequency Gravitational Waves from Graviton-Photon Conversion in the M87 Galaxy
• Full-polarization millimeter wavelength variability of Sagittarius A* during the 2018 EHT campaign