Unrecognized Astrometric Confusion in the Galactic Centre

TL;DR

This paper investigates how unrecognized source confusion in the crowded Galactic Centre introduces astrometric noise, biases orbital parameter estimates, and highlights the need for improved noise modeling in high-precision stellar observations.

Contribution

It provides a self-consistent simulation of source confusion effects, quantifies their impact on orbital estimates, and emphasizes the importance of modeling time-correlated noise for future studies.

Findings

Source confusion causes sub-mas astrometric noise.

Biases in orbital and black hole parameter estimates are significant.

Time-correlated noise models are necessary for accurate parameter inference.

Abstract

The Galactic Centre is a highly crowded stellar field and frequent unrecognized events of source confusion, which involve undetected faint stars, are expected to introduce astrometric noise on a sub-mas level. This confusion noise is the main non-instrumental effect limiting the astrometric accuracy and precision of current near-infrared imaging observations and the long-term monitoring of individual stellar orbits in the vicinity of the central supermassive black hole. We self-consistently simulate the motions of the known and the yet unidentified stars to characterize this noise component and show that a likely consequence of source confusion is a bias in estimates of the stellar orbital elements, as well as the inferred mass and distance of the black hole, in particular if stars are being observed at small projected separations from it, such as the star S2 during pericentre passage. Furthermore, we investigate modeling the effect of source confusion as an additional noise component that is time-correlated, demonstrating a need for improved noise models to obtain trustworthy estimates of the parameters of interest (and their uncertainties) in future astrometric studies.