Optimal estimators for cluster masses using CMB lensing

Sayan Saha

Being the largest collapsed structures in the universe, clusters of galaxies offer valuable insights into the nature of cosmic evolution. What we're really curious about is figuring out how many of these clusters exist at different masses and ages (redshifts). But here's the catch: measuring their mass isn't straightforward. So, we use a cosmic 'weighing scale' that uses faint deflections (weak gravitational lensing) of the oldest light in the universe—known as the cosmic microwave background (CMB) —to find out how massive these clusters really are. In this talk, I'll unveil the power of the Maximum-a-posteriori (MAP) method, showcasing its enhanced precision in measuring cluster masses compared to traditional quadratic estimators (QE). I also show how the MAP estimator is able to mitigate the well-known bias in temperature QE, due to the strong non-Gaussianity of the signal at cluster centre, without any scale cut.

Paper link for reference: https://arxiv.org/abs/2307.11711