Interview with William Hartley

Adjoint Scientifique at University of Geneva

 

What is your current role within the ESA Euclid mission?

I work within a team called OU-PHZ, which we lead in Geneva, and which is a sub part of the overall data processing pipeline, called the Science Ground Segment. Our job is to measure the distances to galaxies, via their redshifts, and to classify the objects that Euclid sees into different types: stars, galaxies and exotic things like quasi-stellar objects (QSOs). Once we've classified objects and measured their distances we determine their properties. For galaxies we measure their total mass in stars, the rate at which they are forming stars and a number of other quantities that our colleagues in the consortium want to use in their work.

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

Yes, there have been! Not all of the surprises have been good in fact. We have had to keep on our toes and quickly identify and fix issues in many different unexpected ways. For instance, we had the ice contamination that was reported earlier in the mission, which was rather surprising in the way it behaved. But thankfully that was solved some time ago. In the Q1 data release, we found a problem with some of our pipeline outputs and had to scramble to make a fix and reprocess some of the data at the last moment. But there have been many positive surprises as well. In particular the lens that was discovered, the Einstein ring, this was fantastic and completely blew me away when I saw this for the first time. I did not expect that we would find something like that, so it was lovely to see and it has really shown what Euclid is capable of. Also, the general quality of the Euclid images - I mean we had simulations of them, expectations of how deep we could go and how precise and sharp these images would be, but actually seeing them has been phenomenal, and it has worked so much better than I thought.

 

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

The things that excite me the most are the things that I do not work on actually, because the wonderful results and final products come almost out of the blue from my perspective, and it is so good to see the breadth of science that is being done with the data. For example, the galaxy morphology catalogue and the link up with the citizen scientists in partnership with galaxy zoo (https://www.esa.int/Science_Exploration/Space_Science/Euclid/Euclid_Galaxy_Zoo_help_us_classify_the_shapes_of_galaxies) and then the discovery of all the strong lenses: so many of them even in this small area (https://www.esa.int/Science_Exploration/Space_Science/Euclid/Euclid_opens_data_treasure_trove_offers_glimpse_of_deep_fields). In my own field of expertise, I contributed to the Q1 data release, and I am hoping to lead a paper that will come out in the late summer, on the stellar mass function of galaxies. Essentially, we count how many galaxies there are of different stellar masses as we look back further in time, and this tells us about how galaxies form and evolve. Q1 includes just one week of Euclid observations; however, this is a data set which is already five times larger than the equivalent data that we had before for this research. So we can get much more accurate measurements of how many galaxies exist in the universe and how massive they are. I am really looking forward to sharing those results, when they come out.

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

Everything is going to get bigger and hopefully better. The scale of the data causes some challenges, but we are up to those, and the really exciting thing that will come is the cosmology. Q1 was not about cosmology because we need a much larger area in order to study cosmology. But this is what the mission was built to achieve and there have been some very tantalizing and interesting results coming out from other telescopes and other analyses that suggest that there is something we do not currently understand about our universe. It is going to be amazing to see whether Euclid can actually confirm that and what we will have to say on the topic even at this early stage in the mission.

Do you have any advice for people who would like to follow a similar career path or to use Euclid data?

Well, the data are public, but they are not necessarily easy to use for people that are unfamiliar with them. We also release nice pictures, which you can dig around in and search for interesting objects. There are several citizen science outreach projects that are going on, and this is a nice way to get involved.
For young people that would like to follow this career path, well it is very heavy in mathematics and physics. From there just explore your interests, be excited, read things and ask questions too. Follow your enthusiasm, I think is the key point. Astronomy is a branch of physics, and the deeper you know physics, the better you understand the universe. I think it is really, really worth your time to do a physics degree if astronomy is your passion.

 

 

For further details on William Hartley’s work on the photometric redshifts and physical properties of galaxies through the PHZ processing function, please refer to the following scientific paper submitted to the arXiv:

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