175-Testing dark energy with the ISW effect in the Euclid mission

  • Doctorat
  • Temps plein
  • Moins de 2 ans
  • Master, DESS, DEA, Bac+5
  • Astronomy, Astrophysics


The various observations of the Universe have been indicating for twenty years now that the expansion of the Universe is accelerating. The standard model of cosmology, known as the LCDM model, describes the Universe as composed of 27% dark matter and 68% dark energy. Understanding the nature of these two energy components remains one of the greatest challenges in contemporary physics.
The future Euclid space mission is dedicated to the study of dark energy and dark matter in the Universe and to test gravity on cosmological scales. Euclid was selected by the European Space Agency (ESA) in 2011 and will be launched in 2022 to probe the Universe over a 6 year-period. These data will revolutionize our ability to map the Universe and better understand the nature of dark energy or put Einstein's General Relativity (GR) in default.
For constraining the dark energy properties, a promising tool relies on the Integrated Sachs-Wolfe effect (ISW). This effect is a secondary anisotropy of the CMB temperature, emerging when CMB photons pass through large overdense or underdense structures in the presence of an accelerated expansion of the Universe: the CMB photons entering overdense regions are blue-shifted and those entering underdense regions are red-shifted. However, the ISW effect is also too small to be observed directly. But the signature of the ISW effect can be observed as a non-zero signal in the cross-correlation between the distribution of foreground tracers of dark matter (such as galaxies) and the temperature of CMB, providing a direct probe of the late-time expansion of the Universe.
Recent work (Kovacs 2021) has shown that the ISW signal amplitude exhibits an excess over the expectations of the standard LCDM model, at the 3 sigma level, especially when the study is applied to superstructures such as supervoids. This effect is not the same depending on the redshift range considered, and an excess is expected for z>1.5 and for z<1.2, in the range of interest of the Euclid mission.
The thesis project focuses on the ISW effect and the cross-correlation between the CMB and cosmic voids, under-dense regions of the Universe. The work of the student will consist in building the void catalogs from galaxy catalogs. Then, the estimators and likelihoods associated with the ISW effect will be developed, validated and implemented in the Euclid pipeline in the framework of the Key project identified in the Euclid XCMB Science Working Group (KP-CMX-3: ISW-GC cross-correlation). This work will be done first using simulation data from the Euclid Collaboration and then using the early Euclid data coming in 2023. A goal of this project is to quantify how the ISW effect impacts onto dark energy and modified gravity parameters.

For more Information, contact Directeur de thèse : escoffier@cppm.in2p3.fr

about the topics and the co-financial partner (found by the lab !). Then, prepare a resumé, a recent transcript and a reference letter from your M2 supervisor/ engineering school director and you will be ready to apply online !


Master in fundamental physics or astrophysics. Interest for cosmology. Programming skills (python, C++), strong motivation, ability to work in large international collaborations.

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