TEASING: a fast and accurate approximation for the low multipole likelihood of the Cosmic Microwave Background temperature

Understand

We explore the low-l likelihood of the angular spectrum C(l) of masked CMB temperature maps using an adaptive importance sampler.

• We find that, in spite of a partial sky coverage, the likelihood distribution of each C(l) closely follows an inverse gamma distribution.
• Our exploration is accurate enough to measure the inverse gamma parameters along with the correlation between multipoles.
• Those quantities are used to build an approximation of the joint posterior distribution of the low-l likelihood.