What is the Hidden Depolarization Mechanism in Low Luminosity AGN?

Abstract

Millimeter wavelength polarimetry of accreting black hole systems can provide a tomographic probe of the accretion flow on a wide range of linear scales. We searched for linear polarization in two low luminosity active galactic nuclei (LLAGN), M81 and M84, using the Combined Array for Millimeter Astronomy (CARMA) and the Submillimeter Array (SMA). We find upper limits of $\sim 1-2\%$ averaging over the full bandwidth and with a rotation measure (RM) synthesis technique. These low polarization fractions, along with similar low values for LLAGN M87 and 3C84, suggest that LLAGN have qualitatively different polarization properties than radio-loud sources and Sgr A*. If the sources are intrinsically polarized and then depolarized by Faraday rotation then we place lower limits on the RM of a few times $10^7\mathrm{rad}{\mathrm{m}}^{-2}$ for the full bandwidth case and $\sim 10^9\mathrm{rad}{\mathrm{m}}^{-2}$ for the RM synthesis analysis. These limits are inconsistent with or marginally consistent with expected accretion flow properties. Alternatively, the sources may be depolarized by cold electrons within a few Schwarzschild radii from the black hole, as suggested by numerical models.

arXiv commentAccepted for publication in ApJL

References in corpus (30)

• Coevolution (Or Not) of Supermassive Black Holes and Host Galaxies
• Advection-Dominated Accretion: Underfed Black Holes and Neutron Stars
• Hot Accretion Flows Around Black Holes
• On the Fate of Gas Accreting at a Low Rate onto a Black Hole
• Faraday Rotation Measure Synthesis
• The Feedback-Regulated Growth of Black Holes and Bulges through Gas Accretion and Starbursts in Cluster Central Dominant Galaxies
• General relativistic magnetohydrodynamical simulations of the jet in M87
• An Unambiguous Detection of Faraday Rotation in Sagittarius A*
• Interferometric Detection of Linear Polarization from Sagittarius A* at 230 GHz
• TADPOL: A 1.3 mm Survey of Dust Polarization in Star-forming Cores and Regions
• Resolved Magnetic-Field Structure and Variability Near the Event Horizon of Sagittarius A*
• A public code for general relativistic, polarised radiative transfer around spinning black holes
• Radiative efficiency, variability and Bondi accretion onto massive black holes: from mechanical to quasar feedback in brightest cluster galaxies
• The size of the jet launching region in M87
• Observational appearance of inefficient accretion flows and jets in 3D GRMHD simulations: Application to Sgr~A*
• The Disc-Jet Symbiosis Emerges: Modeling the Emission of Sagittarius A* with Electron Thermodynamics
• Measuring Mass Accretion Rate onto the Supermassive Black Hole in M 87 Using Faraday Rotation Measure with the Submillimeter Array
• Results from an extensive simultaneous broadband campaign on the underluminous active nucleus M81*: further evidence for mass-scaling accretion in black holes
• Faraday rotation in GRMHD simulations of the jet launching zone of M87
• A Stationary Core with a One-sided Jet in the Center of M81
• Variable Linear Polarization from Sagittarius A*: Evidence for a Hot Turbulent Accretion Flow
• The Linear Polarization of Sagittarius A* I. VLA Spectro-polarimetry at 4.8 and 8.4 GHz
• Numerical Parameter Survey of Nonradiative Black Hole Accretion -- Flow Structure and Variability of the Rotation Measure
• The First Simultaneous 3.5 and 1.3mm Polarimetric Survey of Active Galactic Nuclei in the Northern Sky
• An Attempt to Probe the Radio Jet Collimation Regions in NGC 4278, NGC 4374 (M84), and NGC 6166
• Probing the Parsec-scale Accretion Flow of 3C 84 with Millimeter Polarimetry
• The Submillimeter Array Polarimeter
• Detection of Circular Polarization in M81*
• The First IRAM/PdBI Polarimetric Millimeter Survey of Active Galactic Nuclei. I. Global Properties of the Sample
• A Black Hole Mass-Variability Time Scale Correlation at Submillimeter Wavelengths

Cited by in corpus (9)

• Polarimetric properties of Event Horizon Telescope targets from ALMA
• Faraday rotation in the jet of M87 inside the Bondi radius: indication of winds from hot accretion flows confining the relativistic jet
• ALMA Polarimetry of Sgr A*: Probing the Accretion Flow from the Event Horizon to the Bondi Radius
• Jet collimation and acceleration in the giant radio galaxy NGC 315
• Decomposing the Internal Faraday Rotation of Black Hole Accretion Flows
• Magnetic field at a jet base: extreme Faraday rotation in 3C 273 revealed by ALMA
• Relative depolarization of the black hole photon ring in GRMHD models of Sgr A* and M87*
• Resolving accretion flows in nearby active galactic nuclei with the Event Horizon Telescope
• Low optical polarisation at the core of the optically-thin jet of M87