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The Highly Polarized Dusty Emission Core of Cygnus A

Lopez-Rodriguez, Enrique and Antonucci, Robert and Chary, Ranga-Ram and Kishimoto, Makoto (2018) The Highly Polarized Dusty Emission Core of Cygnus A. Astrophysical Journal Letters, 861 (2). Art. No. L23. ISSN 2041-8205. doi:10.3847/2041-8213/aacff5.

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We report the detection of linearly polarized emission at 53 and 89 μm from the radio-loud active galactic nucleus (AGN) Cygnus A using High-resolution Airborne Wideband Camera-plus (HAWC+) on board the Stratospheric Observatory For Infrared Astronomy (SOFIA). We measure a highly polarized core of 11 ± 3% and 9 ± 2% with a position angle (PA) of polarization of 43° ± 8° and 39° ± 7° at 53 and 89 μm, respectively. We find (1) a synchrotron-dominated core with a flat spectrum (+0.21 ± 0.05) and a turnover at 543 ± 120 μm, which implies synchrotron emission is insignificant in the infrared (IR), and (2) a 2–500 μm bump peaking at ~40 μm described by a blackbody component with color temperature of 107 ± 9 K. The polarized spectral energy distribution (SED) has the same shape as the IR bump of the total flux SED. We observe a change in the PA of polarization of ~20° from 2 to 89 μm, which suggests a change of polarization mechanisms. The ultraviolet, optical, and near-IR (NIR) polarization has been convincingly attributed to scattering by polar dust, consistent with the usual torus scenario, though this scattered component can only be directly observed from the core in the NIR. By contrast, the gradual rotation by ~20° toward the far-IR (FIR), and the near-perfect match between the total and polarized IR bumps, indicate that dust emission from aligned dust grains becomes dominant at 10–100 μm, with a large polarization of 10% at a nearly constant PA. This result suggests that a coherent dusty and magnetic field structure dominates the 10–100 μm emission around the AGN.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Lopez-Rodriguez, Enrique0000-0001-5357-6538
Chary, Ranga-Ram0000-0001-7583-0621
Kishimoto, Makoto0000-0002-2216-3252
Additional Information:© 2018. The American Astronomical Society. Received 2018 May 28; revised 2018 June 19; accepted 2018 June 28; published 2018 July 13. We are grateful to Chris Packham and Edgar Ramirez for their numerous comments that helped to clarify and improve the text. Based on observations made with the NASA/DLR Stratospheric Observatory for Infrared Astronomy (SOFIA). SOFIA is jointly operated by the Universities Space Research Association, Inc. (USRA), under NASA contract NAS2-97001, and the Deutsches SOFIA Institut (DSI) under DLR contract 50 OK 0901 to the University of Stuttgart. Financial support for this work was provided by NASA through award #05_0071 issued by USRA. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. E.L.-R. acknowledges support from the Japanese Society for the Promotion of Science (JSPS) through award PE17783, the National Observatory of Japan (NAOJ) at Mitaka and the Thirty Meter Telescope (TMT) Office at NAOJ-Mitaka for providing a space to work and great collaborations during the short stay in Japan. Facilities: SOFIA (HAWC+) - , Herschel (PACS - , SPIRE) - . Software: astropy (Astropy Collaboration et al. 2013).
Group:Infrared Processing and Analysis Center (IPAC), Thirty Meter Telescope
Funding AgencyGrant Number
Deutsches SOFIA Institut (DSI)DLR 50 OK 0901
Universities Space Research Association05_0071
Japanese Society for the Promotion of Science (JSPS)PE17783
National Observatory of Japan (NAOJ)UNSPECIFIED
Thirty Meter Telescope ProjectUNSPECIFIED
Subject Keywords:galaxies: active; galaxies: individual (Cygnus A) ; galaxies: nuclei; infrared: galaxies; techniques: polarimetric
Issue or Number:2
Record Number:CaltechAUTHORS:20180713-095036943
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Official Citation:Enrique Lopez-Rodriguez et al 2018 ApJL 861 L23
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:87819
Deposited By: George Porter
Deposited On:13 Jul 2018 17:09
Last Modified:15 Nov 2021 20:52

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