Active galactic nuclei (AGN) are unresolvable with modern optical
telescopes since the apparent angular size of the central parsec is
<<0.1 arcsec even for the closest active galaxies. This leads to
difficulties with methods for estimating distances within the AGN.
In particular, determining the size of the dusty torus surrounding
the core is critical for estimating the dust sublimation radius and,
consequently, the physical state of matter in the circumnuclear region,
as well as for determining the masses of central supermassive black
holes by the spectropolarimetric method.
The authors propose a method for estimating the size of a dusty torus
based on reverberation mapping of broad emission lines in polarized light.
In type 1 AGN, the polarization of the broad lines is caused by the
equatorial scattering on the dusty torus; the profile of the broad
lines in polarized light thus acquires specific features. This allows
us to uniquely determine by spectropolarimetry tools whether the
equatorial scattering is the dominant polarization mechanism in
the observed object. The time delay between the signal in the
unpolarized continuum and the polarized broad emission line determines
the distance to the scattering region, where the medium becomes optically
thick and the temperature is low enough for the dust to survive. This
method was first applied to the Seyfert galaxy Mrk 6, whose
spectropolarimetric observations were carried out in 2010-2013 using
the universal spectrograph SCORPIO-2 in the primary focus of the BTA.
The resulting delay was ~100 days, which clarified the size of the
scattering region by a factor of 2 relative to the estimates given
by infrared interferometric observations obtained at the Keck Observatory
telescopes (Hawaii, USA).
Published:
Shablovinskaya E.S., Afanasiev V.L., PopoviÓ L.ó. Measuring the AGN
Sublimation Radius with a New Approach: Reverberation Mapping of Broad
Line Polarization, 2020, ApJ, 892, 118. doi:10.3847/1538-4357/ab7849.
Contact person - Shablovinskaya E.S.,
Trainee researcher at the Laboratory of Spectroscopy and Photometry
of Extragalactic Objects, SAO RAS
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