VAPOLA -- A multiyear, multiband polarization survey of AGNs and Sgr A* at millimeter wavelengths with ALMA. II. Spectropolarimetric properties and their evolution from 2017 to 2023

We aim to present a systematic analysis of the spectropolarimetric properties of a sample of 39 active galactic nuclei (AGNs) and Sagittarius A* observed with the Atacama Large Millimeter/submillimeter Array during five VLBI campaigns between 2017 and 2023. We characterized the compact cores in total intensity and polarization, focusing on the behavior of the linear-polarization (LP) fraction, electric vector position angle (EVPA), and Faraday rotation measure (RM) over time and spectral domains. We investigated both individual objects---such as M87, Sgr A*, 3C273, and 3C279---and ensemble properties of different source classes, including flat-spectrum radio quasars, BLLac objects, and other active galaxies. While total intensity and spectral index are generally stable on weekly timescales, polarization properties often exhibit strong variability, with significant day-to-day changes in LP, EVPA, and RM. Several sources display large EVPA rotations accompanied by variations in LP and RM, in some cases coinciding with flaring activity. We observe that the magnitude of RM increases with observing frequency for all sources for which we have reliable multiband measurements, consistent with Faraday rotation arising in a magnetized sheath surrounding the relativistic jet, although an origin in the accretion flow---particularly in the case of Sgr A*---cannot be ruled out.

Authors

Publication Details

Journal
Astronomy and Astrophysics
Published
2026-10-30
DOI
https://doi.org/10.1051/0004-6361/202662590
Primary Topic
Astrophysical Phenomena and Observations
Type
article
Field-Weighted Citation Impact
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VAPOLA -- A multiyear, multiband polarization survey of AGNs and Sgr A* at millimeter wavelengths with ALMA. II. Spectropolarimetric properties and their evolution from 2017 to 2023

Chi‐kwan Chan, Richard Anantua, J. E. Carlstrom, Charles F. Gammie et al.
Astronomy and Astrophysics
Astrophysical Phenomena and Observations
article

VAPOLA -- A multiyear, multiband polarization survey of AGNs and Sgr A* at millimeter wavelengths with ALMA. II. Spectropolarimetric properties and their evolution from 2017 to 2023

Chi‐kwan Chan, Richard Anantua, J. E. Carlstrom, Charles F. Gammie, S. Britzen, Dominic O. Chang, Ezequiel Albentosa-Ruíz, Roman Gold, Geoffrey C. Bower, Christian M. Fromm, Avery E. Broderick, Ronald Hesper, Sandra Bustamante, Makoto Inoue, Sergio A. Dzib, Jordy Davelaar, Vedant Dhruv, Erandi Chavez, Kazi L. J. Rygl, Dominique Broguière, G. Crew, R. Blundell, Bradford A. Benson, Alejandro Mus, Brissa Gómez Miller, Anne-Kathrin Baczko, Bidisha Bandyopadhyay, Kazuhiro Hada, John Barrett, Peter Louis Galison, Juan Carlos Algaba, Razieh Emami, Kazunori Akiyama, Edward B. Fomalont, Per Friberg, Shiro Ikeda, Vincent L. Fish, Olivier Gentaz, C. Goddi, Boris Georgiev, Mareki Honma, Roger Brissenden, Marianna Foschi, Paul M. Chichura, Jason Dexter, T. M. Crawford, Maciek Wielgus, Mariafelicia De Laurentis, Indu K. Dihingia, Joseph Farah, Antonio Fuentes, Rebecca Azulay, C. M. Violette Impellizzeri, Katherine L. Bouman, Raquel Fraga-Encinas, Michael Bremer, Arturo I. Gómez-Ruiz, Thomas Bronzwaer, Iván Martí-Vidal, Mark Gurwell, Alejandro Cruz-Osorio, Koushik Chatterjee, Dirk Heumann, Nicholas S. Conroy, José Luis Gómez, Keiichi Asada, Rohan Dahale, Lindy Blackburn, Brandon Curd, Joost de Kleuver, Eleni Antonopoulou, John Edward Conway, Roberto García, William T. Freeman, H. Alyson Ford, David R. Ball, David H. Hughes, D. Hoak, W. Alef, Heino Falcke, Minfeng Gu, Ilje Cho, Luis C. Ho, Nicola Marchili, Dan Bintley, Paul Ho, Roger Deane, Daryl Haggard, Andrew Chael, Rohan Ganesh Amanaganti, Douglas Carlos, Ming-Tang Chen, Chin-Shin Chang, Yongjun Chen, Sheperd S. Doeleman, Chih-Wei L. Huang, Xiaopeng Cheng, Michi Bauböck, Yuzhu Cui, Antxon Alberdi
article en

Abstract

We aim to present a systematic analysis of the spectropolarimetric properties of a sample of 39 active galactic nuclei (AGNs) and Sagittarius A* observed with the Atacama Large Millimeter/submillimeter Array during five VLBI campaigns between 2017 and 2023. We characterized the compact cores in total intensity and polarization, focusing on the behavior of the linear-polarization (LP) fraction, electric vector position angle (EVPA), and Faraday rotation measure (RM) over time and spectral domains. We investigated both individual objects---such as M87, Sgr A*, 3C273, and 3C279---and ensemble properties of different source classes, including flat-spectrum radio quasars, BLLac objects, and other active galaxies. While total intensity and spectral index are generally stable on weekly timescales, polarization properties often exhibit strong variability, with significant day-to-day changes in LP, EVPA, and RM. Several sources display large EVPA rotations accompanied by variations in LP and RM, in some cases coinciding with flaring activity. We observe that the magnitude of RM increases with observing frequency for all sources for which we have reliable multiband measurements, consistent with Faraday rotation arising in a magnetized sheath surrounding the relativistic jet, although an origin in the accretion flow---particularly in the case of Sgr A*---cannot be ruled out.

Astronomy and Astrophysics
National Science Foundation, Smithsonian Institution, U.S. Department of Energy, National Aeronautics and Space Administration, Simons Foundation, John Templeton Foundation, Gordon and Betty Moore Foundation, University of Wisconsin-Milwaukee, Massachusetts Institute of Technology, Harvard University, Rice University, University of Texas at San Antonio, National Center for Theoretical Sciences, Heriot-Watt University, CERN, Università degli Studi di Cagliari, Space Telescope Science Institute, Ministerio de Ciencia, Innovación y Universidades, National Radio Astronomy Observatory, POSCO TJ Park Foundation, International Max Planck Research School for Environmental, Cellular and Molecular Microbiology, Joint Institute for Computational Fundamental Science, Flatiron Health, Government of Canada, Leverhulme Trust, European Commission, National Research Foundation, University of Pretoria, Deutsche Forschungsgemeinschaft, Ministry of Education, Culture, Sports, Science and Technology, Canada Research Chairs, Fundação de Amparo à Pesquisa do Estado de São Paulo, National Natural Science Foundation of China, Academia Sinica, Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Chinese Academy of Sciences, Kyungpook National University, Chalmers Tekniska Högskola, China Postdoctoral Science Foundation, Fonds Wetenschappelijk Onderzoek, Nederlandse Organisatie voor Wetenschappelijk Onderzoek, Generalitat Valenciana, Universitat de València, University of Toronto, Korea Astronomy and Space Science Institute, National Research Foundation of Korea, A.G. Leventis Foundation, Max-Planck-Gesellschaft, Vetenskapsrådet, Ministry of Education, India, China Scholarship Council, European Southern Observatory, Ministerio de Ciencia e Innovación, National and Kapodistrian University of Athens, Universidade de São Paulo, Universidad Nacional Autónoma de México, Universidad de Concepción, National Astronomical Observatory of Japan, Vlaamse regering, Istituto Nazionale di Fisica Nucleare, Hellenic Foundation for Research and Innovation, Ministry of Science and ICT, South Korea, Instituto de Astrofísica de Andalucía, Agencia Nacional de Investigación y Desarrollo, National Science and Technology Council, Institut Périmètre de physique théorique, East Asian Core Observatories Association, Toray Science Foundation, University of Illinois at Urbana-Champaign, Office of Science, National Nuclear Security Administration, Physics Division, National Center for Theoretical Sciences, Harvard Data Science Initiative, Harvard University, HORIZON EUROPE Framework Programme, Natural Sciences and Engineering Research Council of Canada, Science and Technology Facilities Council, Japan Society for the Promotion of Science, Fundação para a Ciência e a Tecnologia, Fonds de recherche du Québec – Nature et technologies, Consejo Superior de Investigaciones Científicas, Dirección General de Asuntos del Personal Académico, Universidad Nacional Autónoma de México, National Institutes of Natural Sciences, Agencia Estatal de Investigación, National Key Research and Development Program of China, Office of International Science and Engineering, High Energy Physics, Astrophysics Division, Oak Ridge National Laboratory, Fermilab, Los Alamos National Laboratory
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