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...

0957 + 561 A, B are two QSOs of mag 17 with 5.7 arc s separation at redshift 1.405. Their spectra leave little doubt that they are associated. Difficulties arise in describing them as two distinct objects and the possibility that they are two images of the same object formed by a gravitational lens is discussed.

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.

Combining a new, increased data set of eight quasi‐stellar objects (QSOs) covering the Lyα forest at redshifts 1.5 < z < 3.6 from VLT/UVES observations with previously published results, we have investigated the properties of the Lyα forest at 1.5 < z <4. With the six QSOs covering the Lyα forest at 1.5 < z < 2.5, we have extended previous studies in this redshift range. In particular, we have concentrated on the evolution of the line number density and the clustering of the Lyα forest at z≤ 2.5, where the Lyα forest starts to show some inhomogeneity from sightline to sightline. We have fitted Voigt profiles to the Lyα absorption lines as in previous studies, and have, for two QSOs with zem∼ 2.4, fitted Lyα and higher order of Lyman lines down to 3050 Å simultaneously. This latter approach has been taken in order to study the Lyβ forest at z∼ 2.2 and the higher H i column density Lyα forest in the Lyβ forest region. For a given NH I range, the Lyα forest at 1.5 < z < 4 shows the monotonic evolution, which is governed mainly by the Hubble expansion at this redshift range. In general, the Lyα forest line number density (dn/dz) is best approximated with dn/dz= 6.1(1 +z)2.47 ± 0.18 for the H i column density NH I= 1013.64−17 cm−2 at 1.5 < z < 4. When the results at 0 < z < 1.5 from Hubble Space Telescope (HST) observations are combined, the slow‐down in the number density evolution occurs at z < 1.5. For higher column density clouds at NH i > 1014 cm−2, there is a variation in the line number density from sightline to sightline at z < 2.5. This variation is stronger for higher column density systems, probably due to more gravitationally evolved structures at lower z. The mean H i opacity is at 1.5 < z < 4. HST observations show evidence for slower evolution of at z < 1. For NH i= 1012.5–15 cm−2, the differential column density distribution function, f(NH i), can be best fitted by f(NH I∝NH i−β with β≈ 1.5 for 1.5 < z < 4. When combined with HST observations, the exponent β increases as z decreases at 0 < z < 4 for NH i= 1013–17 cm−2. The correlation strength of the step optical depth correlation function shows the strong evolution from 〈z〉= 3.3 to 〈z〉= 2.1, although there is a large scatter along different sightlines. The analyses of the Lyβ forest at z∼ 2.2 are, in general, in good agreement with those of the Lyα forest.

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