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

## TL;DR

This paper introduces two innovative techniques for identifying strongly lensed quasars and Galactic streams using wide-field survey data, successfully discovering new lenses and streams with potential for further refinement.

## Contribution

The paper presents two novel methods combining outlier detection and GAIA data to improve the identification of quasar lenses and Galactic streams in large surveys.

## Key findings

- Successfully recovered known lensed quasars from SDSS, ATLAS, and DES.
- Discovered new quadruply lensed quasars and Galactic stream candidates.
- Demonstrated the potential to adapt methods for stellar object detection.

## Abstract

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. There is considerable scope for tailoring the WISE-GAIA multiplet search to stellar-like objects, instead of quasar-like, and to automatically detect Galactic streams.