Interview with Giorgia Girardi

2nd year PhD student at University of Padova

 

What is your current role within the ESA Euclid mission?

I am the lead author of one of the papers using Euclid Q1 data (https://www.cosmos.esa.int/web/euclid/q1-data) and I am also finalizing another paper based on Euclid Early Release Observations (ERO) (https://www.cosmos.esa.int/web/euclid/ero-public-release).
I am a member of the Euclid Consortium, and I am part of the Galaxy/Active galactic nuclei (AGN) Evolution Working Group: my work focuses in particular on the study of high-redshift galaxies, up to around redshift 6 or 7. You can think of redshifts as a measure of time or distance. The higher the redshift - the further back in time you are looking, and the more distant the objects are from us.

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

I would not say unexpected. I am studying massive galaxies with a lot of dust, which present red colours, and we select them based on this characteristic. From previous studies, we know that they can contribute in a substantial way to the stellar mass function at the massive end. The stellar mass function is a way of counting how many galaxies exist at different mass ranges, based on the amount of stars they contain. You can compute this at different epochs, to see how their distribution changes as the universe evolves. Until now, the samples we had were relatively small. For example, using the data from the Euclid Early Release Observations of the Perseus field, our sample consisted of only 42 objects. But with the new Euclid Q1 data, we now have a much larger observed area. Even after carefully cleaning the sample - where we removed image artifacts or sources that aren't reliable - we still end up with nearly 4000 galaxies. This larger sample gives us a much better chance to understand how these massive galaxies have formed and evolved over time. At the moment what we have found has confirmed what we already expected based on previous studies.
The most astonishing result in my opinion came from the early release observations of the Perseus Field, where we identified a possible candidate at redshift 14. This is amazing, and two analytical tools already confirmed this photometric redshift. We will need to observe it spectroscopically, but it is very interesting.

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

I am very excited about the wide area of the Euclid Q1 data release. While this is only a small part of what we can expect from Euclid with its continuous observations, I already find the Q1 data release very exciting. With the next release, it will be even more incredible, as we will have a big increase in the amount of data. This will allow us to better constrain the photometric quantities we measure, since some of these can be a bit tricky to estimate. Spectroscopy provides very reliable measurements, while photometric estimates are naturally less certain - though they remain a very powerful tool.
In my own research, I am just really excited about working on galaxies. I really like to look at them and to select them. Every time I do a talk like the one I did at ESLAB 2025 (https://www.cosmos.esa.int/web/euclid-eslab-2025), I am a little nervous that other researchers will not think my research is interesting, but I always get very good response, and the audience often asks questions. That also makes me excited about my work, knowing that it is not only interesting to me but actually also to others.

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

In general, I believe the data collected by Euclid will be groundbreaking for a lot of different fields. In my field specifically I believe we will be able to do really great statistical analysis of the objects observed by Euclid once we receive all the data. It will be the first time that we are able to capture such good resolution and depth over such a large area. James Webb, for instance, offers excellent resolution and depth, but only on much smaller portions of the sky.
So that is my main expectation from Euclid, amazing and detailed data that can lead us to great discoveries.

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

I would say that it depends on the persons age and where they are in the education system. If you are in high school, I would say that in order to get a career in astrophysics you need to endure the first years on the bachelor. You have a lot of physics and mathematics, and when you think about astronomy you might not see the immediate link. However, the link definitely is there, and even if it does not seem to make sense right now, do not get discouraged - as you progress and start working on the things you are passionate about everything will start to come together.
For people at a more advanced stage of their education - for example, those who have already completed a university degree and are thinking about doing a PhD - I believe it is really important to be proactive and reach out professors whose work interests you. Even if you do not know them personally, if you are genuinely interested in their course or research area, sending them an email can be a great way to start a conversation and explore opportunities.
If one is interested in using Euclid data in general, I will say that it is quite easy to enter the Euclid Consortium if you have a valid reason to do so. The consortium is a very welcoming environment, and everyone is really excited about our work. And well, there is tons of data, so we really need a lot of people to work on them.

 

 

For further details on Giorgia Girardi's work on optically faint, red objects in the Euclid Deep Fields, please refer to the following scientific paper submitted to the arXiv:

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