Niu Liu

Source Structure Variability in Multi-wavelength Astrometry

Overview

Many extragalactic radio sources exhibit extended and variable structures. Recent studies based on Gaia data suggest the presence of milliarcsecond-scale optical jets, indicating that source-structure-related systematics are a common challenge in constructing extragalactic reference frames. Because most of these sources are active galactic nuclei (AGNs), their structures can vary significantly over time, leading to apparent positional shifts. Such unpredictable behavior may affect the stability of the reference-frame axes and introduce additional uncertainties in multi-wavelength frame ties. The impact of source structure and its variability therefore needs to be carefully investigated and mitigated in the era of multi-wavelength microarcsecond astrometry.

Direct studies of source-structure effects are mainly feasible in the radio domain, where high-resolution VLBI imaging is available. In contrast, position time series for extragalactic sources will become increasingly available from both the final Gaia catalog and long-term very long baseline interferometry (VLBI) observations. These data make it possible to study the impact of source-structure variability on astrometric positions from a time-domain perspective.

This project investigates the implications of source-structure variability for multi-wavelength source positions. In particular, it focuses on the relation between multi-wavelength positions and source structure, the impact of source-structure variability on apparent positions, and possible strategies for correcting or mitigating these effects. Unlike previous studies based primarily on position time series, this project also uses light curves to identify active periods of AGNs, thereby reducing the influence of systematics unrelated to intrinsic source activity.

Objectives

Funding

National Natural Science Foundation of China

  1. Liu N., Lambert S. B., Arias E. F., Liu J.-C., Zhu Z. Evaluation of the ICRF stability from a position time series analysis. Astronomy & Astrophysics, 659, A75, 2022.

  2. Liu N., Lambert S. B., Charlot P., Zhu Z., Liu J.-C., Jiang N., Wan X.-S., Ding C.-Y. Comparison of multifrequency positions of extragalactic sources from ICRF3 and Gaia EDR3. Astronomy & Astrophysics, 652, A87, 2021.