期刊
ASTROPHYSICAL JOURNAL LETTERS
卷 843, 期 2, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.3847/2041-8213/aa7b2e
关键词
accretion, accretion disks; black hole physics; galaxies: active; galaxies: jets
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 (LLAGNs), M81 and M84, using the Combined Array for Millimeter Astronomy and the Submillimeter Array. We find upper limits of similar to 1%-2% averaging over the full bandwidth and with a rotation measure (RM) synthesis technique. These low polarization fractions, along with similarly low values for LLAGNs M87 and 3C 84, suggest that LLAGNs 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) rad m(-2) for the full bandwidth case and similar to 10(9) rad 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.
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