EDP Sciences
Free access
Volume 434, Number 3, May II 2005
Page(s) 827 - 838
Section Cosmology (including clusters of galaxies)
DOI http://dx.doi.org/10.1051/0004-6361:20041827

A&A 434, 827-838 (2005)
DOI: 10.1051/0004-6361:20041827

VLT/UVES constraints on the cosmological variability of the fine-structure constant

S. A. Levshakov1, M. Centurión2, P. Molaro2 and S. D'Odorico3

1  Department of Theoretical Astrophysics, Ioffe Physico-Technical Institute, 194021 St. Petersburg, Russia
    e-mail: lev@astro.ioffe.rssi.ru
2  Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34131 Trieste, Italy
3  European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany

(Received 10 August 2004 / Accepted 12 January 2005 )

We propose a new methodology for probing the cosmological variability of $\alpha$ from pairs of $\ion{Fe}{ii}$ lines (SIDAM, single ion differential $\alpha$ measurement) observed in individual exposures from a high resolution spectrograph. By this we avoid the influence of the spectral shifts due to (i) ionization inhomogeneities in the absorbers; and (ii) non-zero offsets between different exposures. Applied to the $\ion{Fe}{ii}$ lines of the metal absorption line system at $z_{\rm abs}$ = 1.839 in the spectrum of Q 1101-264 obtained by means of the UV-Visual Echelle Spectrograph (UVES) at the ESO Very Large Telescope (VLT), SIDAM provides $\Delta\alpha/\alpha$ = $(2.4\pm3.8_{\rm stat})\times10^{-6}$. The $z_{\rm abs}$ = 1.15 $\ion{Fe}{ii}$ system toward HE 0515-4414 has been re-analyzed by this method thus obtaining for the combined sample $\Delta\alpha/\alpha$ = $(0.4\pm1.5_{\rm stat})\times10^{-6}$. These values are shifted with respect to the Keck/HIRES mean $\Delta\alpha/\alpha$ = $(-5.7\,\pm\,1.1_{\rm stat})\times10^{-6}$ (Murphy et al. 2004) at very high confidence level (95%). The fundamental photon noise limitation in the $\Delta\alpha/\alpha$ measurement with the VLT/UVES is discussed to figure the prospects for future observations. It is suggested that with a spectrograph of ~10 times the UVES dispersion coupled to a 100 m class telescope the present Oklo level ( $\Delta\alpha/\alpha$ $\geq$ 4.5 $\times$ 10-8) can be achieved along cosmological distances with differential measurements of  $\Delta\alpha/\alpha$.

Key words: cosmology: observations -- line: profiles -- galaxies: quasars: absorption lines -- galaxies: quasars: individual: Q 1101-264 , HE 0515-4414

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