Euclid Quick Data Release (Q1). The Strong Lensing Discovery Engine E -- Ensemble classification of strong gravitational lenses: lessons for Data Release 1

Collaboration
Mar 19, 2025
15 pages
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Abstract: (arXiv)
The Euclid Wide Survey (EWS) is expected to identify of order 100000100\,000 galaxy-galaxy strong lenses across 1400014\,000deg2^2. The Euclid Quick Data Release (Q1) of 63.163.1deg2^2 Euclid images provides an excellent opportunity to test our lens-finding ability, and to verify the anticipated lens frequency in the EWS. Following the Q1 data release, eight machine learning networks from five teams were applied to approximately one million images. This was followed by a citizen science inspection of a subset of around 100000100\,000 images, of which 65%65\% received high network scores, with the remainder randomly selected. The top scoring outputs were inspected by experts to establish confident (grade A), likely (grade B), possible (grade C), and unlikely lenses. In this paper we combine the citizen science and machine learning classifiers into an ensemble, demonstrating that a combined approach can produce a purer and more complete sample than the original individual classifiers. Using the expert-graded subset as ground truth, we find that this ensemble can provide a purity of 52±2%52\pm2\% (grade A/B lenses) with 50%50\% completeness (for context, due to the rarity of lenses a random classifier would have a purity of 0.05%0.05\%). We discuss future lessons for the first major Euclid data release (DR1), where the big-data challenges will become more significant and will require analysing more than 300\sim300 million galaxies, and thus time investment of both experts and citizens must be carefully managed.
Note:
  • Paper submitted as part of the A&A Special Issue `Euclid Quick Data Release (Q1)', 15 pages, 8 figures