About the proper motion of lensed QSOs in Gaia DR2 - pitch slides
| Main Author: | Bombrun, Alex |
|---|---|
| Format: | info Proceeding |
| Terbitan: |
, 2019
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| Subjects: | |
| Online Access: |
https://zenodo.org/record/2634118 |
Daftar Isi:
- Slide 1 QSOs are anchors in the Gaia sky. They have been used to define DR2 reference frame and to analyse the quality of the astrometric solution. The distribution of their normalised proper motions follows a Gaussian with mean 0 and standard deviation close to 1 as one would expect from the error model. Among all the QSOs, the lensed QSOs formed a very particular subset. Being magnified by a foreground galaxy each lensed QSO presents multiple components within a few arcseconds. But contrary to the QSOs, their proper motions do not follow the expected distribution. More than 20% have a component with proper motion larger than 3 sigmas. This plot shows one example of such lensed QSOs. Do we have here some physical effect or is it an artefact of the data processing in DR2? It is more likely an artefact. DR2 processing was done with a single source model. The astrometry has some limitations for objects that are not isolated. Internal studies done last year by DPAC shows the impact of blending on astrometric observations for sources closer to one arc-second. These biases depend on the scanning law, the angular distance and magnitude differences between the sources and might explain the discrepancy seen in the astrometry of the lensed QSOs. This limitation might not only apply to the lensed QSOs but to a lot of other sources. One should be careful with peculiar astrometric objects in DR2. Slide 2 Links to 2 notebooks. One exploring DR2 astrometry of the known lensed QSOs and one illustrating the blending on simulated astrometric observations.