Interview with Michael Walmsley

Dunlap fellow at University of Toronto

 

What is your current role within the ESA Euclid mission?

"I do a couple of different things related to the ESA Euclid mission. I am a scientist with the Euclid Consortium, where I have two main projects. One is to measure detailed galaxy morphology – finding the bars, spiral arms, rings, mergers, and so on in the pictures that Euclid takes. The other project is with the strong lensing science working group, finding galaxy-galaxy strong lenses, where the light from a background galaxy is bent by a massive foreground galaxy, creating these beautiful arcs, which are not only visually pretty cool, if I say so myself, but they are also useful cosmological probes that can tell us about the dark matter wrapped around the foreground galaxy."

Have there been any unexpected findings or surprises in the ESA Euclid mission so far?

"Other than that everything worked," Walmsley said laughing. "We always hoped that Euclid would revolutionize strong lensing. It was predicted at least back in 2015 that Euclid would find something like 100.000 strong lenses, but I don't think we ever quite dared to dream that the prediction would come true. So, it has been a real indication of that forecast and of the quality of the instrument that this is exactly what is happening – we are finding tons of strong lenses. For me, it is often a surprise when things work out, and this was something of a surprise.

I think on the morphology side, what we are noticing is that what we have known about galaxy morphology like bars, rings, and spirals has really historically been focused on ground-based instruments looking at the sky, and when we compare these images with those Euclid takes, we can see so much more detail. It is a little like when the first JWST (James Webb Space Telescope) papers came out, they found there were more disk galaxies than they expected at higher redshifts. Where Hubble (Hubble Space Telescope) had seen amorphous shapes, JWST said 'oh actually, it is quite ordered'.

Euclid is doing a similar thing for more nearby galaxies. We expected them to be more featured, but Euclid can really prove that! And amongst all of those, we were hoping, I think, to find new kinds of galaxies, where you need to have those kinds of counts to reveal it. And I think there is a lot of ongoing work in the Euclid Consortium to try to pick out those mysterious galaxies."

What part of the Q1 data release and your own research are you most excited about?

"You could say that I am a builder - I make catalogues and train machine learning models, and I think the best part about being a builder is to make the catalogues public and let people dive in. So, it is a nice and exciting moment, with the strong lensing catalogue and the visual morphology catalogue to be able to say, 'Show me what you can do with this'.

We are really just at the start of being able to do science with this list of objects, and I am excited to see what the community takes from that. I really want to know for instance: can strong lenses show their substructure in dark matter halos and tell us something about cold dark matter or can Euclid's view of spiral arms perhaps tell us about what forms these spiral arms, which is also still an open question.

I think that especially combined with instruments like the DESI data released at the same day as the Euclid Q1 data, this combination of space-based images and large-scale spectra is really going to transform what we know about galaxies."

Based on the knowledge you have now from the Q1 data release, what are your main expectations from Euclid in the future?

"I think it's going to be hard work.
Q1 was an interesting middle ground. It was a lot of data and not much time to process it, but significant parts could be done manually. For example, in the strong lens search, we had 61 Euclid scientists looking through and vetting all the lens candidates, which were prioritized by the machine learning models, and the citizen scientists. That becomes rapidly harder moving forward, and in fact it will be largely impossible over the next couple of years.

It is sometimes said about start-ups that they do things that don't scale. In this way Euclid felt like running a start-up. You have a bunch of people put together to try to solve a problem, pivoting each day, trying to work out how the pieces fit together, and hacking around where we had to. With DR1, DR2, DR3 it has to become a systematized pipeline, which needs to be robust and automated and scalable, in a way which Q1 has only just started to touch. That transition is my forecast for Euclid in the future."

Do you have any advice for people who would like to use Euclid data?

"For people who want to use Euclid data, I would definitely suggest talking to the instrument teams, the builders, and the organizational unit who put the data together. They have insight into what's coming, what the caveats are, where the best documentation is, and ultimately talking to people are often the best way to find out."

 

 

For further details on Michael Walmsley's work on the morphology and strong lens catalogue, please refer to the following scientific papers published in arXiv:

For more information about the Euclid Q1 release, visit the ESA press release: