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

Understand

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.