Niu Liu

Project: Mitigation of extragalactic source structure

Implication of source structure variability on the multiwavelength positions of extragalactic sources

Descriptions

Most extragalactic sources are known to have an extended radio structure. Recent studies based on Gaia data indicate the existence of the milliarcsecond-scale optical jet, which suggests that the source structure-related systematics is a common issue for constructing the extragalactic reference frame. As most extragalactic sources are active galactic nuclei (AGN), their structure varies due to the strong activity, which leads to abrupt changes in their apparent positions. This kind of unpredictable behavior further makes the axes of the extragalactic reference frame unstable, degrading the long-term stability of the extragalactic frame and introducing new problems to the multiwavelength frame link. Therefore, the effect due to the source structure and its variability should be taken into consideration in the era of multiwavelength micro-arcsecond astrometry. Limited by the image resolution, however, the structure effect can only be studied in the radio domain. In contrast, the position time series for extragalactic sources will be available in the final Gaia catalog and very long baseline interferometry (VLBI) database, making studying the source structure variability effect feasible. We, therefore, propose to investigate the implication of source structure variability on the multiwavelength source positions by addressing three problems: the relation between multiwavelength position and source structure, the impact of source structure variability on multiwavelength positions, and the correction of source structure variability effect. Different from previous studies solely based on the position time series, we will use the light curve to label the active period of the AGN, making our investigation free of various systematics in the position time series.

Funding

National Natural Science Foundation of China

Keywords

Research Output

  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).