A new approach to measuring the dust sublimation radius in active nuclei
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.
Fig.1. Illustration of the equatorial scattering of radiation from the AGN central parts at the inner boundary of the dusty torus. The green arrow shows the unpolarized radiation in the broad emission lines, and the blue arrow shows the polarized radiation in the lines reflected from the scattering region.
Fig.2. A diagram of the distances inside the AGN. The upper part of the figure illustrates the distribution of dust inside the AGN. t1, t2, and t3 correspond to the moments of signal registration from the central source, the broad line region (BLR), and the scattering region, respectively. The lower part corresponds to the scale of distances in the AGN, which are determined in different ways. It can be seen that the distance Rsc, measured using the proposed method of polarimetric reverberation mapping, is the closest to the radius of the dust sublimation, in contrast to the methods of IR reverberation mapping ("K-band RM") and IR interferometry ("IR IF").