Quasar Lenses and Galactic Streams: Outlier Selection and GAIA Multiplet Detection

Understand

I describe two novel techniques originally devised to select strongly lensed quasar candidates in wide-field surveys.

• The first relies on outlier selection in optical and mid-infrared magnitude space; the second combines mid-infrared colour selection with GAIA spatial resolution, to identify multiplets of objects with quasar-like colours.
• Both methods have already been applied successfully to the SDSS, ATLAS and DES footprints: besides recovering known lenses from previous searches, they have led to new discoveries, including quadruply lensed quasars, which are rare within the rare-object class of quasar lenses.
• As a serendipitous by-product, at least four candidate Galactic streams in the South have been identified among foreground contaminants.