26 November: Louis Gabarra

Speaker: Louis Gabarra (University of Oxford)

Date: Wednesday 26 November 2025

Time: 15:00

Location: Physics 3.21

When a Spectrometer Becomes an Imager: Exploring Euclid’s Hidden Potential

The Euclid Mission is now in operation and already producing highly promising results across many fields of astrophysics, using both photometric and spectroscopic observations. Euclid’s primary goal is cosmological: it will map the dark-matter distribution through measurements of cosmic shear using diffraction-limited imaging and will trace the baryonic acoustic oscillation (BAO) scale at different cosmic epochs to probe the evolution of dark energy. The weak-lensing and BAO analyses will rely on an unprecedented dataset of over one billion photometric and more than 35 million spectroscopic measurements, spanning more than 10 billion years of cosmic history (up to redshift ≈ 2) and covering most of the extragalactic sky.

The slitless spectroscopic configuration of Euclid, combined with the huge volume of data, poses major challenges for data processing. Optimising the balance between data compression, computational feasibility, and scientific outcome has required a series of trade-offs. While these compromises are tuned for large-scale Euclid cosmological analyses, where a fraction of false detections can be tolerated, they become critical when studying smaller samples, individual galaxies, or populations outside the main cosmological sample.

In this talk, I will present the main analysis trade-offs adopted by the Euclid consortium for cosmological purposes and how these choices have motivated the development of complementary data-reduction pipelines aimed at other scientific goals. I will describe a new approach that uncovers previously hidden capabilities of the Euclid slitless spectrometer, showing that it can, in effect, function as an imager. Finally, I will highlight the emerging scientific opportunities enabled by these emission-line maps, which open an unexpected new window for galaxy-evolution studies, foster synergies with other telescopes, and enable spatially resolved spectroscopy within the Euclid mission framework.