Volume 526, February 2011
|Number of page(s)||4|
|Published online||04 January 2011|
Letters to the Editor
The evolution of the cosmic microwave background temperature⋆
Measurements of TCMB at high redshift from carbon monoxide excitation
Departamento de AstronomíaUniversidad de Chile,
e-mail: firstname.lastname@example.org; email@example.com
2 Université Paris 6, Institut d’Astrophysique de Paris, CNRS UMR 7095, 98bis bd Arago, 75014 Paris, France
3 Inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, 411 007 Pune, India
4 European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago 19, Chile
Accepted: 13 December 2010
A milestone of modern cosmology was the prediction and serendipitous discovery of the cosmic microwave background (CMB), the radiation leftover 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) × (1 + z)1−β K with β = −0.007 ± 0.027, a more than two-fold improvement in precision. The measurements are consistent with the standard (i.e. adiabatic, β = 0) Big-Bang model and provide a strong constraint on the effective equation of state of decaying dark energy (i.e. weff = −0.996 ± 0.025).
Key words: cosmology: observations / cosmic background radiation / quasars: absorption lines
© ESO, 2011
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