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, M. G. Kozlov1,5,6
1Universität Hamburg, Germany
2Ioffe Physical-Technical Institute, Saint Petersburg, Russia
3Observatoire de Paris, LERMA, France
4Université de Toulouse, UPS-OMP, France
5Petersburg Nuclear Physics Institute, Gatchina, Russia
6Saint-Petersburg Electrotechnical University "LETI", Russia

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 [CI] 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 (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 mu, 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 dFF and dmm, one obtains for the relative change in alpha the estimate Δα/α < 8×10-6, which is at present the tightest limit on daa at early cosmological epochs.

Reference
Levshakov S.A. et al. 2012, Astron. Astrophys. Lett. (accepted), arXiv:1203.3649.


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