State of the Universe

The Purely Astrometric Quasar Survey: A Colour-blind approach to quasar identification

by Prof. Jens-Kristian Krogager (Institut d'Astrophysique de Paris (France))

Friday, March 12, 2021 from to (Asia/Kolkata)
at Zoom
Description
Quasars are widely used in astrophysics to probe various environments, ranging from large-scale studies of the intergalactic medium through Lyman-alpha absorption and clustering to galactic-scale studies of interstellar and circumgalactic media. Moreover, the details of quasar evolution and how this is reflected in the various observational phenomena are still poorly understood. One main limitation to quasar studies, in general, is the pre-selection for spectroscopic observations. The largest spectroscopic quasar samples to date are selected based on optical colours with inhomogeneous inclusion of multi-wavelength data to increase purity. Such identifications lead to potential biases in the derived quasar demographic and can have severe consequences for foreground absorption studies. Various other methods for selecting quasars based on different parts of the quasar energy distribution have been employed (e.g., radio, X-ray or IR), yet current samples are small. In this talk, I will highlight our efforts to obtain the first colour-independent quasar sample by selecting candidates for observation purely based on astrometry from Gaia. This method allows us to select a sample of bright quasars with no assumption on the shape of the SED. The talk will focus on the implications for studies of foreground absorption systems as well as the quasar demographic in general. 
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