STAGE How well can we measure the galaxy-galaxy lensing signal in realistic Euclid data?

The Euclid satellite, to be launched in 2022, will provide the most direct insights yet on the nature of the accelerated expansion of the Universe. The power of Euclid stems from a unique survey which will measure the positions and shapes of over a billion galaxies. These shape measurements probe the underlying dark matter distribution; combined with distances they will enable a uniquely discriminating probe of our cosmological model. However, measuring shapes on real data is challenging as many instrumental effects pollute the images and must be correctly accounted for during data processing. It is unclear how the correction of these instrumental effects can affect the shape measurements.
The only way to resolve this is by simulating at a pixel level both observations and processing. The objective of this internship is to understand how this processing chain affects a single, well-known signal: the galaxy-galaxy lensing signal.
The galaxy-galaxy lensing signal provides a direct measurement of the dark matter profile of individual galaxies and mass of each associated dark matter halo, a crucial quantity to understand galaxy evolution. Although this signal is considerably stronger than the relatively faint cosmic shear signal that Euclid seeks to measure, it still subject to similar systematic errors related to the knowledge of the instrumental response function and biases inherent in shape measurement.
This stage aims to make the first measurement of the gravitational galaxy-galaxy lensing signal in simulated Euclid VIS images after processing and to compare how the measured signal compares with the input signal. The results will immediately inform our knowledge of the performance of the Euclid ground segment and how well Euclid will be able to measure the dark matter profiles of ordinary galaxies.
This project will be carried out at the IAP (Institut d'Astrophysique de Paris, 98 bis Boulevard Arago, Paris 75014) under the direction of Henry J. McCracken and Raphael Gavazzi.