A near-infrared, optical and ultraviolet polarimetric and timing investigation of complex equatorial dusty structures

Abstract

Context. From stars to active galactic nuclei, many astrophysical systems are surrounded by an equatorial distribution of dusty material that are, in a number of cases, spatially unresolved even with cutting edge facilities. Aims. In this paper, we investigate if and how one can determine the unresolved and heterogeneous morphology of dust distribution around a central bright source using time-resolved polarimetric observations. Methods. We use polarized radiative transfer simulations to study a sample of circumnuclear dusty morphologies. We explore a grid of uniform, fragmented, density-stratified, geometrically-variable models in the near-infrared, optical and ultraviolet bands, and present their distinctive time-dependent polarimetric signatures. Results. As expected, varying the structure of the obscuring equatorial disk has a deep impact on the inclination-dependent flux, polarization degree and angle, and time-lags we observe. We find that stratified media are distinguishable by time-resolved polarimetric observations, and that the expected polarization is much higher in the infrared band than in the ultraviolet. However, due to the physical scales imposed by dust sublimation, the average time-lags between the total and polarized fluxes are important (months to years), lengthening the observational campaigns necessary to break more sophisticated (and therefore also more degenerated) models. In the ultraviolet band, time-lags are slightly shorter than in the infrared or optical bands, and, coupled to lower diluting starlight fluxes, time-resolved polarimetry in the UV appears more promising for future campaigns.