Rare strong lens gems emerging from the Space Warps ESA Euclid Data Release 1 search
A few months ago, we started the full-scale search for strong gravitational lenses in the ESA Euclid Data Release 1 (DR1) survey. While we are carefully analysing your classifications, in this blog post we highlight some of our favourite strong lens candidates that you’ve collectively found in this dataset.
Congratulations!! You’ve now passed the milestone of an incredible 5 million classifications since the first ESA Euclid Quick Data Release 1 (Q1) lens search began in 2024, including 2.7 million in the current ESA Euclid DR1 search. We have been completely blown away, and are excitedly analysing all your classifications! While the lens search and our analysis continue, we wanted to highlight some of the stunning strong lens candidates that you have found and let you know what’s happening next with the lens search.
Beyond the fascinating individual systems we highlight in this blog post, thousands of other lens candidates are emerging from your collective classifications – such a large population which will help to revolutionise the study of strong lenses. Prior to Euclid DR1 only a few hundred strong gravitational lenses had been identified in space-based imaging and so the thousands of lens systems which you have found will change how we can study these systems, enabling us to analyse the strong lens population as a whole.
Amongst this treasure trove of lens systems are some scientific gems:
First up is a lensed quasar (ID: 119727051); this has four lensed images forming a ‘quad’ configuration. The light from the quasar (a bright supermassive black-hole at the centre of a distant galaxy) is strong enough to outshine both the light of the deflector or lens galaxy and that of the host galaxy it resides in. Unlike galaxy-galaxy strong lenses, the light from the central deflector can’t be seen in the image. Quasars, in particular quadruply imaged quasars like this one, are particularly useful probes of cosmology. Light emitted from the background quasar will arrive at the Earth at different times depending on which of the four routes (corresponding to the 4 lensed images) that it takes. The arrival time of the emitted light is dependent on the degree of lensing (how much mass there is in the deflector galaxy), and the expansion rate of the universe. From the separation of the lensed images we can estimate the mass of the deflector or lens and therefore, by measuring the time delay of each of the four images, strongly lensed quasars can help to constrain the expansion of the universe!
Next up are two lens systems with bright dust lanes (119696543 and 119705025 ). In both of these systems, at least 3 lensed images are visible (in the left example the counter-image is likely hidden behind the smaller satellite galaxy to the right). These systems highlight the superb resolution of the Euclid telescope, as well as the benefits of colour imaging which helps distinguish the dust lanes from lensed arcs or tidal features.
This is an example of a candidate double-source-plane lens (ID: 119665581) – here the deflector galaxy is lensing two different background galaxies, creating two sets of lensed arcs. These are very rare systems even within strongly lensed systems since they require the close alignment of two source galaxies with the deflector galaxy rather than just one. They are also especially useful for a range of astrophysical and cosmological studies, for example the two Einstein rings allow us to tightly constrain how much mass is present in the deflector galaxy, and where it is most concentrated.
This final system (ID: 121188143) suggests that the lensed background galaxy has interesting structure. In this image you can see four images of the same bright, white blob but around these finer stellar filaments can be seen. This implies that the background galaxy has a central bright component and more extended fainter structure around it. By developing a model of such systems, we can remove the distortion caused by gravitational lensing and reconstruct what the source galaxy really looks like. The extra detail visible in the lensed arcs can help us produce a sharper, higher-resolution image of the background galaxy than would be possible if we were observing the same galaxy without the amplification and magnification by strong lensing.
These systems are just a small snapshot of the lensed systems you have already identified. Behind the scenes, we are analysing all of your classifications both in classify and refine in preparation for the public release of all the Euclid DR1 images in November this year. In the meantime, we are adding the second batch of approximately 50,000 Euclid DR1 images to Space Warps Classify. These systems were flagged as lens candidates by a new machine learning network, and we’re keen to see what you think! This network used multiple bands (colours) in order to classify the lensed images, so it will be really interesting to see if different types of strong lens systems appear in this second batch compared to the first.
Thank you again for your classifications and we look forward to discussing further exciting strong lens systems with you!
The Space Warps ESA Euclid Strong Lens team.
Narrowing down the ESA Euclid lens sample
Last year we launched Space Warps Refine, a project where we asked you to be more discerning than ‘Classify’ and grade the lens candidates according to your confidence they were genuine lenses. We took your collective grades and have been poring over the interesting results. Phil Holloway shares his summary of Refine below along with an exciting update on the Euclid DR1 lens candidates.
In recent years, telescope surveys have grown larger, deeper, and higher in the detail (or resolution) we can see in their imaging. Eventually we expect to discover more than 100,000 strong lenses. The space-based Euclid telescope is enabling the discovery of many of these systems, and through your tremendous efforts we have already made great progress using the Euclid Q1 data (summarised here and here).
Traditionally, following a lens search, researchers have sorted candidates into classes based on their confidence that each is a genuine lens system. However, with so many promising lens candidates arriving from Euclid, the number of lens candidates is huge!! Last year in Space Warps Refine, you did a tremendous job in helping us find the best method for separating the most compelling lens candidates from the more ambiguous ones, while also identifying candidates that our team might have overlooked in their inspection. We want to share some of those results with you.
Given the huge number of lens candidates that we will identify in forthcoming Euclid data releases, minimising the number of classifications required for each system will be key. However, as you have experienced, lens grading can be subjective and we don’t want to miss genuine systems so crowd classifications are really important. Your classifications in Space Warps Refine show that a consensus grade can be reached much faster for definite lenses and definite non-lenses than those that are more ambiguous intermediate systems (‘probable’ and ‘possible’ lenses). We find the same result when using your classifications and when using the grades from strong lens researchers. This is really good news because we want to find the most reliable and highest grade systems and get rid of the lowest grade systems as fast as possible. Rapidly reaching a consensus grade on these systems means we can start working on them early and then focus on more ambiguous intermediate systems which can be much more subjective.
Your independent classifications have also allowed us to see what the researchers overlooked. Below are a selection of systems which you graded higher than the researchers.
Center: This system has a blue arc to the right-hand side of the central galaxy. Researchers graded this as a ‘possible’ lens. The blue arc appears to be deflected round the central galaxy but no counter-image is visible (a tell-tale sign of a strong lens). While the mass of the central galaxy has likely caused this deflection, it may not be massive enough to produce multiple-imaging. Nevertheless, gravitational lensing is at work here!
Right: Researchers graded this system as a non-lens, whereas Space Warps volunteers classed this as a probable lens system. It does have some classic characteristic features of a strong lens so perhaps the researchers were too hasty! There is a blue arc on the right-hand-side, deflected round the central galaxy. On the left-hand-side there is a small bright clump, with a similar colour to the larger arc. This configuration is plausible for an arc + counter-image lensed system. However, there are some features which are more unusual for a lens – there is a faint arc extending further upwards anticlockwise from the right-hand arc, and the central galaxy is relatively small (faint) to produce lensing. We can’t be sure what is happening here – is it an unusual lens system, or an imposter?
A huge thank you to everyone who took part in Space Warps Refine last year – your contributions have been truly incredible! I’ll post the draft paper soon so you can see the full analysis.
What’s next? The results from last year’s Space Warps Refine are hugely exciting, and are informing our strategy for inspecting the huge number of strong lens candidates which will be identifiable with the Euclid satellite and beyond. Indeed, your success means we would like to ask for you help in “Refining” the early candidates that are emerging from your incredible classifications on the first batch of Euclid Data Release 1 data. So many great candidates are emerging, please join us and have a closer look at these beautiful and fascinating finds!!
WOW: A million classifications!!
After just two weeks, we have surpassed an incredible 1 million classifications on the new ESA Euclid data! Many congratulations to all of the Space community on reaching this milestone! We have been blown away by your amazing contributions – a huge thank you to each and every one of you! In this blog post, Phil Holloway shares some of his favourites from the fantastic systems the Space Warps community has found so far.
First up is a double-source plane lens (ID: 119647449), where two different galaxies, at different distances from us, are lensed by the same foreground galaxy. Double-source plane systems are very rare because they require all three galaxies (the lens, and two sources) to be almost perfectly aligned. This system shows two rings around the central lens, and is reminiscent of the Jackpot lens in its almost circular nature. Such a clear double-source-plane lens will no doubt be studied for many years to come.
The second system is a face-on spiral lens (ID: 119679277). Most lens galaxies are elliptical and are typically made up of old stars. Occasionally, spiral galaxies can act as lenses, since they have the most massive and older stars in their central regions, though when they do they are usually seen edge-on since this maximises the amount of mass along our line-of-sight which makes lensing more likely. Face-on spiral lenses, such as shown below, are practically unheard of! This lens, alongside a beautiful spiral galaxy complete with bright blue star-forming clumps, is a really fantastic find.
Finally, we have an edge-on lens surrounded by a near-complete Einstein ring (ID: 119674016). There are two darker lines extending horizontally along the length of the lens – this is dust within the lens galaxy, which acts to absorb some of the background light. The light of the source galaxy is relatively white/yellow, which indicates it could be made up of older stars, have dust that turns blue light red or be very distant (further analysis is needed to identify which it is), unlike many lensed sources which appear blue because of their young stellar population.
These amazing finds are just a small fraction of the lenses you’ve discovered so far and we can’t wait to see what else you’ll find. Thanks again for all your amazing classifications, happy classifying and we’ll see you on Talk!
Space Warps 