We previously reported Keck telescope observations suggesting a smaller value of the fine structure constant, α, at high redshift. New Very Large Telescope (VLT) data, probing a different direction in the universe, shows an inverse evolution; α increases at high redshift. Although the pattern could be due to as yet undetected systematic effects, with the systematics as presently understood the combined dataset fits a spatial dipole, significant at the 4.2σ level, in the direction right ascension 17.5±0.9 hours, declination −58±9 degrees. The independent VLT and Keck samples give consistent dipole directions and amplitudes, as do high and low redshift samples. A search for systematics, using observations duplicated at both telescopes, reveals none so far which emulate this result.PACS numbers: 06.20. Jr, 95.30.Dr, 95.30.Sf, 98.62.Ra, 98.80.Es, 98.80.Jk Quasar spectroscopy as a test of fundamental physics.-The vast light-travel times to distant quasars allow us to probe physics at high redshift. The relative wavenumbers, ω z , of atomic transitions detected at redshift z = λ obs /λ lab − 1, can be compared with laboratory values, ω 0 , via the relationshipwhere the coefficient Q measures the sensitivity of a given transition to a change in α. The variation in both magnitude and sign of Q for different transitions is a significant advantage of the Many Multiplet method [1, 2], helping to combat potential systematics.The first application of this method, 30 measurements of ∆α/α = (α z − α 0 ) /α 0 , indicated a smaller α at high redshift at the 3σ significance level. By 2004 we had made 143 measurements of α covering a wide redshift range, using further data from the Keck telescope obtained by 3 separate groups, supporting our earlier findings, that towards that general direction in the universe at least, α may have been smaller at high redshift, at the 5σ level [3][4][5]. The constant factor at that point was (undesirably) the telescope and spectrograph.New data from the VLT.-We have now analysed a large dataset from a different observatory, the VLT. Full details and searches for systematic errors will be given elsewhere [6,7]. Here we summarize the evidence for spatial variation in α emerging from the combined Keck+VLT samples. Quasar spectra, obtained from the ESO Science Archive, were selected, prioritising primarily by expected signal to noise but with some preference given to higher redshift objects and to objects giving more extensive sky coverage. The ESO midas pipeline was used for the first data reduction step, including wavelength calibration, although enhancements were made to derive a more robust and accurate wavelength solution from an improved selection of thorium-argon calibration lamp emission lines [8]. Echelle spectral orders from several exposures of a given quasar were combined using uves popler [9]. A total of 60 quasar spectra from the VLT have been used for the present work, yielding 153 absorption systems. Absorption systems were identified via a careful visual search of each spectrum, us...

Quasar absorption lines provide a precise test of whether the fine‐structure constant, α, is the same in different places and through cosmological time. We present a new analysis of a large sample of quasar absorption‐line spectra obtained using the Ultraviolet and Visual Echelle Spectrograph (UVES) on the Very Large Telescope (VLT) in Chile. We apply the many‐multiplet method to derive values of Δα/α≡ (αz−α0)/α0 from 154 absorbers, and combine these values with 141 values from previous observations at the Keck Observatory in Hawaii. In the VLT sample, we find evidence that α increases with increasing cosmological distance from Earth. However, as previously shown, the Keck sample provided evidence for a smaller α in the distant absorption clouds. Upon combining the samples, an apparent variation of α across the sky emerges which is well represented by an angular dipole model pointing in the direction RA = 17.3 ± 1.0 h and Dec. =−61°± 10°, with amplitude . The dipole model is required at the 4.1σ statistical significance level over a simple monopole model where α is the same across the sky (but possibly different from the current laboratory value). The data sets reveal remarkable consistencies: (i) the directions of dipoles fitted to the VLT and Keck samples separately agree; (ii) the directions of dipoles fitted to z < 1.6 and z > 1.6 cuts of the combined VLT+Keck samples agree; and (iii) in the equatorial region of the dipole, where both the Keck and VLT samples contribute a significant number of absorbers, there is no evidence for inconsistency between Keck and VLT. The amplitude of the dipole is clearly larger at higher redshift. Assuming a dipole‐only (i.e. no‐monopole) model whose amplitude grows proportionally with ‘lookback‐time distance’ (r=ct, where t is the lookback time), the amplitude is (1.1 ± 0.2) × 10−6 GLyr−1 and the model is significant at the 4.2σ confidence level over the null model (Δα/α≡ 0). We apply robustness checks and demonstrate that the dipole effect does not originate from a small subset of the absorbers or spectra. We present an analysis of systematic effects, and are unable to identify any single systematic effect which can emulate the observed variation in α. To the best of our knowledge, this result is not in conflict with any other observational or experimental result.

We present a strong constraint on variation of the proton-to-electron mass ratio mu over cosmological time scales using molecular hydrogen transitions in optical quasar spectra. Using high quality spectra of quasars Q0405-443, Q0347-383, and Q0528-250, variation in micro relative to the present day value is limited to Deltamicro/micro=(2.6+/-3.0)x10;{-6}. We reduce systematic errors compared to previous works by substantially improving the spectral wavelength calibration method and by fitting absorption profiles to the forest of hydrogen Lyman alpha transitions surrounding each H2 transition. Our results are consistent with no variation, and inconsistent with a previous approximately 4sigma detection of mu variation involving Q0405-443 and Q0347-383. If the results of this work and those suggesting that alpha may be varying are both correct, then this would tend to disfavor certain grand unification models.

Molecular hydrogen transitions in quasar spectra can be used to constrain variation in the proton‐to‐electron mass ratio, μ≡ mp/me, at high redshifts (z ≳ 2). We present here an analysis of a new spectrum of the quasar Q0528−250, obtained on Very Large Telescope (VLT)/Ultraviolet and Visual Echelle Spectrograph (UVES), and analyse the well‐known H2 absorber at z = 2.811 in this spectrum. For the first time we detect deuterated molecular hydrogen (HD) in this system with a column density of log10(N/cm−2) = 13.27 ± 0.07; HD is sensitive to variation in μ, and so we include it in our analysis. Using 76 H2 and seven HD transitions we constrain variation in μ from the current laboratory value to be Δμ/μ= (0.3 ± 3.2stat± 1.9sys) × 10−6, which is consistent with no cosmological variation in μ, as well as with previous results from other H2/HD absorbers. The main sources of systematic uncertainty relate to accurate wavelength calibration of the spectra and the re‐dispersion of multiple telescope exposures on to the one pixel grid.

The detection of a spatial variation of the fine-structure constant, α, based on study of quasar absorption systems has recently been reported [1]. The physics that causes this α-variation should have other observable manifestations, and this motivates us to look for complementary astrophysical effects. In this paper we propose a method to test whether spatial variation of fundamental constants existed during the epoch of big bang nucleosynthesis. Using existing measurements of primordial deuterium abundance we find very weak indications that such a signature might exist, but the paucity of measurements precludes any firm conclusion. We also examine existing quasar absorption spectra data that are sensitive to variation of the electron-to-proton mass ratio µ and x = α 2 µgp for spatial variation.

We present an analysis of 23 absorption systems along the lines of sight towards 18 quasars in the redshift range of 0.4 z abs 2.3 observed on the Very Large Telescope (VLT) using the Ultraviolet and Visual Echelle Spectrograph (UVES). Considering both statistical and systematic error contributions we find a robust estimate of the weighted mean deviation of the fine-structure constant from its current, laboratory value of ∆α/α = (0.22 ± 0.23) × 10 −5 , consistent with the dipole variation reported in Webb et al. (2011) and King et al. (2012). This paper also examines modelling methodologies and systematic effects. In particular we focus on the consequences of fitting quasar absorption systems with too few absorbing components and of selectively fitting only the stronger components in an absorption complex. We show that using insufficient continuum regions around an absorption complex causes a significant increase in the scatter of a sample of ∆α/α measurements, thus unnecessarily reducing the overall precision. We further show that fitting absorption systems with too few velocity components also results in a significant increase in the scatter of ∆α/α measurements, and in addition causes ∆α/α error estimates to be systematically underestimated. These results thus identify some of the potential pitfalls in analysis techniques and provide a guide for future analyses.

Abstract. Recent attempts to constrain cosmological variation in the fine structure constant, α, using quasar absorption lines have yielded two statistical samples which initially appear to be inconsistent. One of these samples was subsequently demonstrated to not pass consistency tests; it appears that the optimisation algorithm used to fit the model to the spectra failed. Nevertheless, the results of the other hinge on the robustness of the spectral fitting program VPFIT, which has been tested through simulation but not through direct exploration of the likelihood function. We present the application of Markov Chain Monte Carlo (MCMC) methods to this problem, and demonstrate that VPFIT produces similar values and uncertainties for Δα/α, the fractional change in the fine structure constant, as our MCMC algorithm, and thus that VPFIT is reliable. Recent years have seen sustained interest in attempting to determine the value of the fine structure constant, α in the early universe using quasar absorption lines. Differing atomic/ionic transitions have different sensitivities to α, and thus by fitting Voigt profiles to the observed profiles of quasar absorption systems, we can mesure Δα/α = (α z − α0 )/α0 , where αz is the value of α at redshift z and α0 is the laboratory value. Murphy et al. (2004) have found that Δα/α = (−0.57 ±0.11) ×10 −5 from 143 quasar absorption systems, whereas Chand et al. (2004) reported Δα/α = (−0.06 ± 0.06) × 10 −5 from 23 measurements. However, Murphy et al. (2008) demonstrate that the analysis of Chand et al. suffers significant flaws which render both the estimate and statistical precision for Δα/α of Chand et al. unreliable.We apply Markov Chain Monte Carlo (MCMC) methods to investigate the z = 1.018, z = 2.029 and z = 1.748 absorption systems toward quasars LBQS 2206−1958, LBQS 0013−0029 and Q 0551−366 respectively. In particular, we confirm for these cases that the spectral fitting program VPFIT, used by Murphy et al. (2004), produces good estimates of Δα/α and appropriate statistical uncertainties, and thus we regard the results of Murphy et al. (2004) as robust.

Theories unifying gravity with other interactions suggest spatial and temporal variation of fundamental "constants" in the Universe. A change in the fine structure constant, α = e 2 / c, could be detected via shifts in the frequencies of atomic transitions in quasar absorption systems. Recent studies using 140 absorption systems from the Keck telescope and 153 from the Very Large Telescope, suggest that α varies spatially [1]. That is, in one direction on the sky α seems to have been smaller at the time of absorption, while in the opposite direction it seems to have been larger.To continue this study we need accurate laboratory measurements of atomic transition frequencies. The aim of this paper is to provide a compilation of transitions of importance to the search for α variation. They are E1 transitions to the ground state in several different atoms and ions, with wavelengths ranging from around 900 -6000Å, and require an accuracy of better than 10 −4Å. We discuss isotope shift measurements that are needed in order to resolve systematic effects in the study. The coefficients of sensitivity to α-variation (q) are also presented.