EDP Sciences
Free Access
Volume 478, Number 2, February I 2008
Page(s) L27 - L30
Section Letters
DOI https://doi.org/10.1051/0004-6361:20078200

A&A 478, L27-L30 (2008)
DOI: 10.1051/0004-6361:20078200


Is there a need and another way to measure the cosmic microwave background temperature more accurately?

J. Chluba1 and R. A. Sunyaev1, 2

1  Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching bei München, Germany
    e-mail: jchluba@mpa-garching.mpg.de
2  Space Research Institute, Russian Academy of Sciences, Profsoyuznaya 84/32, 117997 Moscow, Russia

(Received 2 July 2007 / Accepted 4 December 2007)

The recombination history of the Universe depends exponentially on the temperature, T0, of the cosmic microwave background. Therefore tiny changes of T0 are expected to lead to significant changes in the free electron fraction. Here we show that even the current $1\sigma$-uncertainty in the value of T0 results in more than half a percent ambiguity in the ionization history, and more than $0.1\%$ uncertainty in the TT and EE power spectra at small angular scales. We discuss how the value of T0 affects the highly redshifted cosmological hydrogen recombination spectrum and demonstrate that T0 could, in principle, be measured by looking at the low frequency distortions of the cosmic microwave background spectrum. For this no absolute measurements are necessary, but sensitivities on the level of ~$ 30\,$nK are required to extract the quasi-periodic frequency-dependent signal with typical $\Delta \nu/\nu\sim 0.1$ coming from cosmological recombination. We also briefly mention the possibility of obtaining additional information on the specific entropy of the Universe, and other cosmological parameters.

Key words: cosmology: cosmic microwave background -- cosmology: theory -- cosmology: cosmological parameters

© ESO 2008