Portraits of Euclideans – Louis Gabarra

Euclid is a space mission planned, built, and operated by more than 2000 scientists and engineers across Europe and other countries. In Portraits of Euclideans we showcase the people behind the mission.

In this portrait: Louis Gabarra, Euclid Research Scientist in Galaxy Evolution and Spectroscopy

  • Can you tell us something about your background?

Before entering in science and in my academic career, I was working as an engineer in something totally different. I used to work in mass production in automotive industry. My job was to optimise manufacturing practices using Lean manufacturing practices and best project management practices (Critical Chain Project Management). At a certain point, I decided to go back to studies and this is when I started to study astrophysics and then a Ph.D. in astrophysics.

  • Could you tell us something about the place you grew up in?

I grew up in Paris. For me, Paris has been an amazing place where I had the opportunity to meet people from different background. And this is like in the Euclid Consortium! This is something I really love about, working with people from all over Europe and even beyond.

  • So you studied in Paris as well?

I studied in Lyon, where I spent five years to do my master degree in engineering. Being a student in Lyon was a great experience. This city is very welcoming and has a lot to offer, a great history, great location close to the Alpes to get some fresh air, excellent food, and a particularly dynamic student and cultural life.  

  • Maybe you could tell us a little bit also about the other work that you’ve done. I know that you’ve been teaching as well?

Yes, that was the way how I went from engineering to science. I loved my job as an engineer but I missed physics and maths. When you work as an engineer, then you take responsibilities and you don’t do physics and maths any more. So, I decided to change my path and I went to teach physics in a French school. And then, while I was teaching physics in Ethiopia, I realized that I loved it, I loved science. I love teaching too. There were these telescopes available that nobody was using at that time and this has been a game changer in my career. I asked myself “Can I take the lead of the astronomy club?”; and then I did. I actually had to work a lot to study what we could observe because initially I didn’t know coming from the automotive industry. This is when I got into it and I enjoyed it maybe even more than the students. I was my own student. And, at a certain point I had even the privilege to teach it to others and to share this very newborn passion with the students.

Teaching, learning… this is what brought me back to study, and this experience in particular.

  • That’s at this very moment that you decided to be an astrophysicist?

At this very moment, I was remembering that when I was younger, I was good in maths and physics. But, could I still do it? Could I take that challenge? I knew it was far away. I would miss the bases that I knew by heart when I was studying. I would start to refresh all this knowledge.

Astrophysics was very scary to me because I remember speaking to a friend and I said that I wanted to study astrophysics, but I don’t want to deal with the formulas. Once I got into the studies, I realized this was crazy. I realized, I was more thinking about astronomy from an amateur point of view, where you can talk about planets and discoveries without entering too much into in the science behind. But when you are entering the field, you see what produces those results is actually all about science. And I realized also programming.And I realized also programming.So this is in this context that I decided to go back to study.

  • Where do you currently work and live?

I currently work and live in Oxford. I am just starting a new position here. It’s actually very related to what I have learned in Euclid. Euclid was a great experience to put together and to develop different expertise. For me, it was perfect because there were ways to put my engineering skills to work on the development of the instrument. The Euclid Consortium has this kind of very wide, broad range of expertise that goes from this technical aspect of the instrument up to the science. And so, I could also do science at the same time, studying galaxies and their physical properties. Now that I am in Oxford, I am applying what I have learned on Euclid to the MOSAIC spectrograph of the biggest telescope ever built, a 40 meters mirror in Chile, the Extremely Large Telescope.

So, I am working on developing the MOSAIC spectrograph while doing some science combining Euclid data with data from another spectrograph (WEAVE) to study galaxy evolution. Combining different spectrographs is indeed a very powerful way to get the most to do science (the sum is greater than the parts) where both instruments can be used for mutual calibration. What is interesting when you develop an instrument is also to know what we will do with this instrument. Starting from an idea that when you start there is a state of the art of knowledge of science that will be different when this instrument will finally work. This needed flexibility is why it it important to do science while developing the instrument and it’s something that I learned in Euclid and I will go on with this kind of hybrid approach that can really make you understand the data and be ready for surprises.

  • I guess you will get to travel to Chile?

With everything that we hear every day, I’m not any more into this. I don’t want to take the plane. Especially since this area is a very sensitive area. So, it’s a huge responsibility that we have as astronomers. It’s very important that minimize as much as we can our trips. I will go there only if it is necessary.

  • What is your role in the Euclid Consortium?

My role was to test the performance of the NISP instrument but in the context of the science that it will do. Euclid ends up studying dark matter and dark energy. But whatever the thing you want to study in space, you will observe galaxies. So basically, when you want to do cosmology, at a certain point you need to understand what are the galaxies that you will observe. Therefore, I was working on what kind of population of galaxies we will detect and how the galaxy will be detected by the instrument. So, I work on this kind of tests that we can call end-to-end approach, from the pixels to the cosmology probes. I was studying, scrutinizing this data processing pipeline while do science on galaxy evolution.

In my current work on Euclid, I will take some of this information and combine them with data collected from other telescopes. So, I am trying to see how we can combine Euclid data in synergy with other spectrographs to get the most of the data to optimize our analysis. In particular, I am doing dust attenuation study using an optical spectrograph (WEAVE) together with the near infrared Euclid spectrograph which can be very efficient to study the most dusty star formation regions.

  • What is the most interesting or exciting thing about your job?

The most exciting thing about my job is that you don’t have any limit to what you can study. If you want to push the limits of what you can understand, you will never reach the end. The only limit is your curiosity, and this is just fascinating.

  • If it is a never-ending journey, how do you fit that in a project that is very limited in time?

I think that when you work on such project, everything that you learn during the process is absolutely crucial for the next steps. The telescope we are working on is the results from experiences in the past. This can be useful to understand the critical aspects of the development of an instrument, the science, how to define science for an instrument, etc. So, this does not really matter that the project is ending. The science that has been defined for Euclid relies on knowledge that has been developed for decades. What we are doing right now is going to be crucial to understand and plan the next challenges.

  • Why is the near infrared and thereby the NISP instrument so important for Euclid?

Just nearby the visible light, which is only a small fraction of the spectrum. There is the near-infrared than can’t be seen with our eyes and can barely be studied from earth, because of the atmosphere that emits a lot of light in this wavelength range. This is it important, because when we look at galaxies far away, their light becomes redder and redder. This is the so-called redshift. A lot of information can be extracted from the visible light but we can track these features only on nearby galaxies. As soon as we want to track these very well-studied well-calibrated features on further away galaxies, they are all redshifted in the near-infrared. So, we are losing an amazing part of the spectrum. This is why we send the telescope into space. The NISP instrument of Euclid will provide the first large map of the sky in the near infrared.

  • Why do you need models and simulations of Euclid targets already before the start of the observations?

The simulations are useful for two main purposes. The first one is to get trained with our algorithm. You make fake images and you try to extract the spectra. You make the community ready for the real data. The second purpose is to make some performance forecast for the science that you are planning. Let’s say that if you want to reach it a goal, you need to understand how you can reach it with your instrument. For instance your want to run simulations to study the optimal exposure time. You want it long enough to detect galaxies, but, since you want to scan the entire sky, you are also limited in the duration. So there is a trade-off to optimize the exposure time for the purpose of the survey.

  • How do you simulate galaxies and what are the observational effects you simulate?

First, we have been doing ground-tests where we illuminated the NISP focal plane in all the ways you can imagine to characterized the optical performance. Second of all, when Euclid will be in the sky, we will have some background light detected by our detectors, while our Milky Way will absorb some of the light from the galaxies we want to observe. The ecliptic plane, which is the plane where we have all the planets, also emits some light because there is a bit of dust that scatters the light from the sun, the so-called zodiacal light. Then, the last thing that you need is to give a representative sample of the galaxies that you want to spot. Then you have to put these all together to make some forecast of the instrument performance.

It’s hard to simulate galaxies. At some point, I tried to count the lines from the different scripts and I stopped at 100,000 lines. I couldn’t even open all the scripts. It’s a huge script that required years of experience from different people to build and you are never sure that you are simulating properly. From the real data, it will also be a way to calibrate our simulator. So we will still do simulations.

One can say, why do you make simulation even after launch? Well, because there are some aspects that you cannot get easily from the data. When you want to test the effect on specific variables such as, for example, what would happen in such event if we have so many galaxies organized with this density, can we detect them? From the data, we will calibrate the simulator, and using the simulations, we will calibrate the data! This ping pong game will be performed during the entire missions. 

  • If you are not doing science, you have an idea what you would do?

I would certainly be teaching more for kids around ten and thirteen, when they don’t know yet whether they are subjectively ‘good’ or ‘bad’ at doing physics and maths. To keep their motivation, at this age, it is fascinating.

  • What do you do for fun?

Outside work I play football and I like to share moments with people around a good glass of wine or beer. Right now, my kids are my fun.

  • Do you have any recommendations (movies, theatre, music…)?

Nothing specific but during your studies or you work, never stop reading books, watching movies. For example, I’m fascinated by the French New Wave which is a French art movement in the 60s-70s, with directors like Godard, it gives me a timeless perspective on our current time. I mean that you also need to keep good quality in your readings, movies, music, in your way to access culture in general. It is important to keep an interest in Art, whatever it is. Science is a kind of art at the end. As our work will also inspire artists, we need to be inspired by artists. 

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