A precise and accurate determination of the cosmic microwave background temperature at z=0.89

TL;DR

This paper measures the cosmic microwave background temperature at redshift 0.89 with high precision, confirming the standard cosmological model's predictions and improving the accuracy of such measurements.

Contribution

It introduces a novel Monte-Carlo Markov Chain method combined with non-LTE radiative transfer modeling to precisely determine Tcmb at z=0.89.

Findings

Measured Tcmb=5.08 ± 0.10 K at z=0.89

Results are consistent with standard cosmological predictions

Achieved the most precise Tcmb measurement at z>0 to date

Abstract

According to the Big Bang theory and as a consequence of adiabatic expansion of the Universe, the temperature of the cosmic microwave background (CMB) increases linearly with redshift. This relation is, however, poorly explored, and detection of any deviation would directly lead to (astro-)physics beyond the standard model. We aim at measuring the temperature of the CMB with an accuracy of a few percent at z=0.89 toward the molecular absorber in the galaxy lensing the quasar PKS1830-211. We adopt a Monte-Carlo Markov Chain approach, coupled with predictions from the non-LTE radiative transfer code RADEX, to solve the excitation of a set of various molecular species directly from their spectra. We determine Tcmb=5.08 pm 0.10 K at 68% confidence level. Our measurement is consistent with the value Tcmb=5.14 K predicted by the standard cosmological model with adiabatic expansion of the Universe. This is the most precise determination of Tcmb at z>0 to date.