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 into multi-wavelength frame ties. The effects of source structure and its variability therefore need to be carefully investigated and mitigated in the era of multi-wavelength microarcsecond astrometry.

Direct studies of source-structure effects are primarily feasible in the radio domain, where high-resolution VLBI imaging is available. Position time series for extragalactic sources will also become increasingly available from future Gaia data releases and long-term very long baseline interferometry (VLBI) observations. These data make it possible to investigate the effects 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. It focuses on the relation between multi-wavelength astrometric positions and source structure, the impact of structural variability on apparent source positions, and possible strategies for correcting or mitigating these effects. In addition to position time series, the project uses light curves to identify active periods of AGNs and distinguish intrinsic source variability from unrelated astrometric systematics.

Objectives

Funding

  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. A&A 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. A&A 652, A87 (2021).