The evolution of the Cosmic Microwave Background Temperature: Measurements of TCMB at high redshift from carbon monoxide excitation

TL;DR

This study measures the Cosmic Microwave Background temperature at high redshift using CO absorption lines, confirming the standard Big-Bang model and constraining dark energy properties with improved precision.

Contribution

It provides new high-redshift TCMB measurements from CO absorption lines, refining the temperature evolution and testing cosmological models.

Findings

TCMB(z)=(2.725+/-0.002) x (1+z)^(1-beta) K with beta=-0.007+/-0.027

Results are consistent with the standard Big-Bang model

Tight constraints on dark energy equation of state w_eff=-0.996+/-0.025

Abstract

A milestone of modern cosmology was the prediction and serendipitous discovery of the Cosmic Microwave Background (CMB), the radiation left over after decoupling from matter in the early evolutionary stages of the Universe. A prediction of the standard hot Big-Bang model is the linear increase with redshift of the black-body temperature of the CMB (TCMB). This radiation excites the rotational levels of some interstellar molecules, including carbon monoxide (CO), which can serve as cosmic thermometers. Using three new and two previously reported CO absorption-line systems detected in quasar spectra during a systematic survey carried out using VLT/UVES, we constrain the evolution of TCMB to z~3. Combining our precise measurements with previous constraints, we obtain TCMB(z)=(2.725+/-0.002)x(1+z)^(1-beta) K with beta=-0.007+/-0.027, a more than two-fold improvement in precision. The measurements are consistent with the standard (i.e. adiabatic, beta=0) Big-Bang model and provide a strong constraint on the effective equation of state of decaying dark energy (i.e. w_eff=-0.996+/-0.025).