ALMA polarimetry measures magnetically aligned dust grains in the torus of NGC 1068

Abstract

The obscuring structure surrounding active galactic nuclei (AGN) can be explained as a dust and gas flow cycle that fundamentally connects the AGN with their host galaxies. This structure is believed to be associated with dusty winds driven by radiation pressure. However, the role of magnetic fields, which are invoked in almost all models for accretion onto a supermassive black hole and outflows, is not thoroughly studied. Here we report the first detection of polarized thermal emission by means of magnetically aligned dust grains in the dusty torus of NGC 1068 using ALMA Cycle 4 polarimetric dust continuum observations ($0.07"$, $4.2$ pc; 348.5 GHz, $860$ $\mu$m). The polarized torus has an asymmetric variation across the equatorial axis with a peak polarization of $3.7\pm 0.5$\% and position angle of $109\pm 2^{\circ }$ (B-vector) at $\sim 8$ pc east from the core. We compute synthetic polarimetric observations of magnetically aligned dust grains assuming a toroidal magnetic field and homogeneous grain alignment. We conclude that the measured 860 $\mu$m continuum polarization arises from magnetically aligned dust grains in an optically thin region of the torus. The asymmetric polarization across the equatorial axis of the torus arises from 1) an inhomogeneous optical depth, and 2) a variation of the velocity dispersion, i.e. variation of the magnetic field turbulence at sub-pc scales, from the eastern to the western region of the torus. These observations and modeling constrain the torus properties beyond spectral energy distribution results. This study strongly supports that magnetic fields up to a few pc contribute to the accretion flow onto the active nuclei.

arXiv comment19 pages, 11 figures (Accepted for Publication to ApJ)

References in corpus (43)

• Astropy: A Community Python Package for Astronomy
• Dust Grain Size Distributions and Extinction in the Milky Way, LMC, and SMC
• Density, Velocity, and Magnetic Field Structure in Turbulent Molecular Cloud Models
• AGN Dusty Tori: I. Handling of Clumpy Media
• Molecular line emission in NGC1068 imaged with ALMA. I An AGN-driven outflow in the dense molecular gas
• Obscured Active Galactic Nuclei
• The power of relativistic jets is larger than the luminosity of their accretion disks
• Planck intermediate results. XIX. An overview of the polarized thermal emission from Galactic dust
• Defining the intrinsic AGN infrared spectral energy distribution and measuring its contribution to the infrared output of composite galaxies
• Diagnostics of irradiated dense gas in galaxy nuclei. II. A grid of XDR and PDR models
• The close environments of accreting massive black holes are shaped by radiative feedback
• Dispersion of Magnetic Fields in Molecular Clouds. I
• Torus and AGN properties of nearby Seyfert galaxies: Results from fitting IR spectral energy distributions and spectroscopy
• ALMA resolves the torus of NGC 1068: continuum and molecular line emission
• The Parsec-scale Radio Structure of NGC 1068 and the Nature of the Nuclear Radio Source
• Radiation-driven Fountain and Origin of Torus around Active Galactic Nuclei
• Planck intermediate results. XX. Comparison of polarized thermal emission from Galactic dust with simulations of MHD turbulence
• ALMA images the many faces of the NGC1068 torus and its surroundings
• Inclination-Induced Polarization of Scattered Millimeter Radiation from Protoplanetary Disks: The Case of HL Tau
• ALMA Reveals Transition of Polarization Pattern with Wavelength in HL Tau's Disk
• High-Velocity Bipolar Molecular Emission from an AGN Torus
• ALMA Reveals an Inhomogeneous Compact Rotating Dense Molecular Torus at the NGC 1068 Nucleus
• Polarized Sub-Millimetre Emission from Filamentary Molecular Clouds
• Grain alignment induced by radiative torques: effects of internal relaxation of energy and complex radiation fields
• On the difference of torus geometry between hidden and non-hidden broad line active galactic nuclei
• Change of Magnetic Field$-$Gas Alignment at Gravity-Driven Alfvénic Transition in Molecular Clouds: Implications for Dust Polarization Observations
• ALMA 0.1-0.2 arcsec resolution imaging of the NGC 1068 nucleus - compact dense molecular gas emission at the putative AGN location
• The Location of the Nucleus of NGC 1068 and the Three-dimensional Structure of Its Nuclear Region
• Mid Infrared Spectral Energy Distribution of NGC 1068 with 0.1 arcsec Spatial Resolution
• AGN obscuration through dusty infrared dominated flows. I. Radiation-hydrodynamics solution for the wind
• The emission and distribution of dust of the torus of NGC 1068
• Nonlinear Hydromagnetic Wave Support of a Stratified Molecular Cloud
• Modeling Dust Polarization Observations of Molecular Clouds through MHD Simulations
• Silicate Dust in Active Galactic Nuclei
• Gemini Mid-IR Polarimetry of NGC1068: Polarized Structures Around the Nucleus
• A Multi-Transition Study of Molecules toward NGC 1068 based on High-Resolution Imaging Observations with ALMA
• Near-Infrared Polarimetric Adaptive Optics Observations of NGC 1068: A torus created by a hydromagnetic outflow wind
• Radiation feedback on dusty clouds during Seyfert activity
• HST NICMOS Observations of the Polarization of NGC 1068
• A complete disclosure of the hidden type-1 AGN in NGC 1068 thanks to 52 years of broadband polarimetric observation
• Mid-infrared imaging- and spectro-polarimetric subarcsecond observations of NGC 1068
• On the Optical-to-Silicate Extinction Ratio as a Probe of the Dust Size in Active Galactic Nuclei
• Parsec-scale obscuring accretion disk with large scale magnetic field in AGN

Cited by in corpus (23)

• The Galaxy Activity, Torus and Outflow Survey (GATOS) I. ALMA images of dusty molecular tori in Seyfert galaxies
• The Galaxy Activity, Torus and Outflow Survey (GATOS): II. Torus and polar dust emission in nearby Seyfert galaxies
• ALMA 0.02"-resolution observations reveal HCN-abundance-enhanced counter-rotating and outflowing dense molecular gas at the NGC 1068 nucleus
• The strength and structure of the magnetic field in the galactic outflow of M82
• High-energy Neutrinos from the Inner Circumnuclear Region of NGC 1068
• Dynamical evidence of the sub-parsec counter-rotating disc for a close binary of supermassive black holes in the nucleus of NGC 1068
• Hypercubes of AGN Tori (HYPERCAT) -- I. Models and Image Morphology
• High Sensitivity Observations of the Water Megamasers of NGC 1068: Precise Astrometry and Detailed Kinematics
• Hypercubes of AGN Tori (HYPERCAT) -- II. Resolving the Torus with Extremely Large Telescopes
• Dissecting the active galactic nucleus in Circinus IV. MUSE NFM observations unveil a tuning-fork ionised gas morphology
• The complex infrared dust continuum emission of NGC1068: ground-based N- and Q-band spectroscopy and new radiative transfer models
• On the origin of radio-loudness in active galactic nuclei using far-infrared polarimetric observations
• The Centimeter to Submillimeter Broad Band Radio Spectrum of the Central Compact Component in A Nearby Type-II Seyfert Galaxy NGC 1068
• JWST reveals the diversity of nuclear obscuring dust in nearby AGN: nuclear isolation of MIRI/MRS datacubes and continuum spectral fitting
• ALMA polarimetry of radio-quiet AGNs
• Modelling Grain Rotational Disruption by Radiative Torques and Extinction of Active Galactic Nuclei
• The 2175 Å~ Bump Features in FeLoBAL Quasars: One Indicator of MW-like Dust in the Nuclear Region of Quasar
• High angular resolution polarimetric imaging of the nucleus of NGC 1068: Disentangling the polarising mechanisms
• Systematic Study of the Inner Structure of Molecular Tori in Nearby U/LIRGs using Velocity Decomposition of CO Rovibrational Absorption Lines
• Study of the Inner Structure of the Molecular Torus in IRAS 08572+3915 NW with Velocity Decomposition of CO Rovibrational Absorption Lines
• Gamma rays as leptonic portals to energetic neutrinos: a new Monte Carlo approach
• The properties of the obscuring material of an AGNs sample from mid-IR and X-ray simultaneous fitting
• From the Circumnuclear Disk in the Galactic Center to thick, obscuring tori of AGNs -- Modelling the molecular emission of a parsec-scale torus as found in NGC1068