A sharper view of the late-time Universe:

Joint Analyses of cosmic microwave background and galaxy surveys


  • Karim Benabed, Institut d’astrophysique de Paris, UMR7095, CNRS/Sorbonne Université 
  • Elisabeth Krause, Physics, UArizona


The accelerated expansion of the Universe is the most surprising cosmological discovery in decades. It is not predicted by the standard model of particle physics; the amplitude of the leading theoretical explanation, vacuum energy Λ , and observations differ by tens of orders of magnitude. This has inspired a new generation of ambitious surveys to determine the fundamental nature of cosmic acceleration through measurements of the dark energy equation of state parameters and by confronting measurements from the early and late Universe. This proposal combines two leading cosmology research groups with complementary expertise to unlock the constraining power of combining Cosmic Microwave Background (CMB) measurements and galaxy imaging surveys.

The most stringent constraints from these surveys will be achieved if the information from multiple cosmological probes and incorporate synergies across surveys and wavelengths can be combined.

While the advantages of multi-probe analyses are unquestioned, the development and implementation of the required analysis techniques are still in their infancy: to date, most cosmological analyses only combine probes that are at most weakly correlated and assume that their systematics are independent.

More specifically, we plan to constrain cosmic structure formation and dark energy through a joint analysis of CMB lensing, the imprint of hot gas on the CMB (thermal Sunyaev-Zeldovich effect, tSZ), galaxy clustering and lensing of galaxies, and their cross-correlations – 10 different two-point statistics. 

The proposed project will quantify the importance of such a joint analysis approach for the ambitious upcoming CMB surveys and the Euclid mission, Rubin Observatory, and Roman Space Telescope large-scale structure surveys; as a pilot study,  this analysis method will be demonstrated on existing data from the South Pole Telescope (SPT, a CMB survey) and galaxy catalogs from DES.

The 2 graduate student thesis projects will be integrated into the two teams' broader research activities, further enhancing and expanding the already existing collaboration. Additionally, the students will have the opportunity to participate in the Dark Energy Survey and South Pole Telescope collaborations, which are large international research collaborations and will add to the students interdisciplinary training. The topics in this proposal have been identified by the international community as high priority research areas (Alonso et al., 2021) and will contribute immensely to the broader research community.