An upper limit to the variation in the fundamental constants at redshift z = 5.2
S. A. Levshakov1,2, F. Combes3, F. Boone4, I. I. Agafonova1,2, D. Reimers1 and M. G. Kozlov1,5,6
1 Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
2 Ioffe Physical-Technical Institute, Polytekhnicheskaya Str. 26, 194021 St. Petersburg, Russia
3 Observatoire de Paris, LERMA, CNRS, 61 Av. de l’Observatoire, 75014 Paris, France
4 Université de Toulouse, UPS-OMP, CNRS, IRAP, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
5 Petersburg Nuclear Physics Institute, 188300 Gatchina, Russia
6 St. Petersburg Electrotechnical University “LETI”, Prof. Popov Str. 5, 197376 St. Petersburg, Russia
Received: 15 February 2012
Accepted: 15 March 2012
Aims. We constrain a hypothetical variation in the fundamental physical constants over the course of cosmic time.
Methods. We use unique observations of the CO(7–6) rotational line and the [C i] 3P2 - 3P1 fine-structure line towards a lensed galaxy at redshift z = 5.2 to constrain temporal variations in the constant F = α2/μ, where μ is the electron-to-proton mass ratio and α is the fine-structure constant. The relative change in F between z = 0 and z = 5.2, ΔF/F = (Fobs − Flab)/Flab, is estimated from the radial velocity offset, ΔV = Vrot − Vfs, between the rotational transitions in carbon monoxide and the fine-structure transition in atomic carbon.
Results. We find a conservative value ΔV = (1 ± 5) km s-1 (1σ C.L.), which when interpreted in terms of ΔF/F gives ΔF/F < 2 × 10-5. Independent methods restrict the μ-variations at the level of Δμ/μ < 1 × 10-7 at z = 0.7 (look-back time tz0.7 = 6.4 Gyr). Assuming that temporal variations in μ, if any, are linear, this leads to an upper limit on Δμ/μ < 2 × 10-7 at z = 5.2 (tz5.2 = 12.9 Gyr). From both constraints on ΔF/F and Δμ/μ , one obtains for the relative change in α the estimate Δα/α < 8 × 10-6, which is at present the tightest limit on Δα/α at early cosmological epochs.
Key words: elementary particles / line: profiles / techniques: radial velocities / galaxies: high-redshift
© ESO, 2012