The European Space Agency’s (ESA) Euclid space mission aims to reveal the nature of dark energy, the mysterious cause of the observed accelerated expansion of the universe. Identifying dark energy is arguably the most profound question facing fundamental Physics today, because of its connection between the quantum world and gravity. Euclid will measure the dark energy equation-of-state (EoS), which is to say that it will determine if dark energy is constant or varies with time, a key distinction for theoretical understanding. Euclid will achieve the most significant improvement in EoS measurement precision among the large programs currently planned for the foreseeable future. The proposed thesis project will construct the Euclid galaxy cluster catalog and use it as a cosmological probe to measure the EoS; this will involve contributions to the mission science ground segment and scientific analysis of the survey.

The doctoral project consists of the following:

• Mapping the Euclid cluster selection function over intrinsic cluster parameters, its implementation in the Euclid cosmological likelihood pipeline, and participation in the Euclid cluster cosmology analysis.
• Euclid mass measurements for objects in the Planck cosmology cluster catalog, and cosmology reanalysis of the Planck cluster catalog using Euclid mass measurements.
• Comparison of Planck cluster catalog results to Euclid cluster catalog cosmology results.

Our team at APC has used clusters as a cosmological probe for years, successfully applying modeling and mitigation methods to the Planck satellite mission.  These methods are being adapted to the more complex Euclid optical-NIR data set. Our expertise lies specifically in modeling the cluster selection function, identification of counterparts, mass measurements, and likelihood analyses. The student will work with our other doctoral students and postdoctoral fellows on the project. S/he will join the Cosmology and Euclid Teams at APC.