Astronomy & Astrophysics

Free access article

A&A 381, L64-L67 (2002)
DOI: 10.1051/0004-6361:20011698

Letter

The cosmic microwave background radiation temperature at $\vec{z}_\mathsf{abs} = \mathsf$ toward QSO 0347-3819

P. Molaro¹, S. A. Levshakov², M. Dessauges-Zavadsky^{3, 4} and S. D'Odorico³

¹ Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 34131 Trieste, Italy
² Division of Theoretical Astrophysics, National Astronomical Observatory, Mitaka, Tokyo 181-8588, Japan
³ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
⁴ Observatoire de Genève, 1290 Sauverny, Switzerland

(Received 5 June 2001 / Accepted 28 November 2001)

Abstract
From the analysis of the C ⁺ fine-structure population ratio in the damped Ly $\alpha$ system at $z_{\rm abs}$ = 3.025 toward the quasar Q0347-3819 we derive an upper bound of $14.6\pm0.2$ K on the cosmic microwave background temperature ( $T_{\rm CMBR}$ ) regardless the presence of other different excitation mechanisms. The analysis of the ground state rotational level populations of H ₂ detected in the system reveals a Galactic-type UV radiation field ruling out UV pumping as an important excitation mechanism for C ⁺. The low dust content estimated from the Cr/Zn ratio indicates that the IR dust emission can also be neglected. When the collisional excitation is considered, we measure a temperature for the cosmic background radiation of $T_{\rm CMBR}$ = 12.1^+1.7_-3.2 K. The results are in agreement with the $T_{\rm CMBR}$ = $10.968 \pm0.004$ K predicted by the hot Big Bang cosmology at $z_{\rm abs}$ = 3.025.

Key words: cosmology: observations: cosmic microwave background -- quasars: absorption lines: individual: Q0347-3819

Offprint request: P. Molaro, molaro@oat.ts.astro.it

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Letter

The cosmic microwave background radiation temperature at toward QSO 0347-3819

The cosmic microwave background radiation temperature at $\vec{z}_\mathsf{abs} = \mathsf$ toward QSO 0347-3819