Euclid: The Early Release Observations Lens Search Experiment

We investigated the ability of the Euclid telescope to detect galaxy-scale gravitational lenses. To do so, we performed a systematic visual inspection of the 0.7,deg^2 Euclid Early Release Observations data towards the Perseus cluster using both the high-resolution band and the lower-resolution and bands. Each extended source brighter than magnitude 23 in was inspected by 41 expert human classifiers. This amounts to 12,086 stamps of times . We found 3 grade A and 13 grade B candidates. We assessed the validity of these 16 candidates by modelling them and checking that they are consistent with a single source lensed by a plausible mass distribution. Five of the candidates pass this check, five others are rejected by the modelling, and six are inconclusive. deg $galaxy-galaxy lenses that are both discoverable through visual inspection and have valid lens models. This is consistent with theoretical forecasts of discoverable galaxy-galaxy lenses in Euclid. Our five modelled lenses have Einstein radii in the range ang E but their Einstein radius distribution is on the higher side when compared to theoretical forecasts. This suggests that our methodology is likely missing small-Einstein-radius systems. Whilst it is implausible to visually inspect the full Euclid dataset, our results corroborate the promise that Euclid will ultimately deliver a sample of around$10^5$ galaxy-scale lenses.