Spectroastrometric Reverberation Mapping of Broad-line Regions by Yan-Rong Li et al. on Tuesday 29 November

Spectroastrometry measures source astrometry as a function of

wavelength/velocity. Reverberations of spectroastrometric signals naturally

arise in broad-line regions (BLRs) of active galactic nuclei as a result of the

continuum variations that drive responses of the broad emission lines with time

delays. Such signals provide a new diagnostic for mapping BLR kinematics and

geometry, complementary to the traditional intensity reverberation mapping (RM)

technique. We present the generic mathematical formulism for spectroastrometric

RM and show that under realistic parameters of a phenomenological BLR model,

the spectroastrometric reverberation signals vary on a level of several to tens

of microarcseconds, depending on the BLR size, continuum variability, and

angular-size distance. We also derive the analytical expressions of

spectroastrometric RM for an inclined ring-like BLR. We develop a Bayesian

framework with a sophisticated Monte-Carlo sampling technique to analyze

spectroastrometic data and infer the BLR properties, including the central

black hole mass and angular-size distance. We demonstrate the potential of

spectroastrometric RM in spatially resolving BLR kinematics and geometry

through a suite of simulation tests. An application to realistic observation

data of 3C~273 obtains tentative, but enlightening results, reinforcing the

practical feasibility of conducting spectroastrometric RM experiments on bright

AGNs with the operating Very Large Telescope Interferometer as well as possibly

with the planned next-generation 30m-class telescopes.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.14767v1