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 describe the design, development, and performance of HAWK-I, the new High-Acuity Wide-field K-band Imager for ESO's Very Large Telescope, which is equipped with a mosaic of four 2 k × 2 k arrays and operates from 0.9−2.4 μm over 7.5 × 7.5 with 0.1 pixels. A novel feature is the use of all reflective optics that, together with filters of excellent throughput and detectors of high quantum efficiency, has yielded an extremely high throughput. Commissioning and science verification observations have already delivered a variety of excellent and deep images that demonstrate its high scientific potential for addressing important astrophysical questions of current interest.

HAWK-I (High Acuity, Wide field K-band Imaging) is a 0.9 µm -2.5 µm wide field near infrared imager designed to sample the best images delivered over a large field of 7.5 arcmin x 7.5 arcmin. HAWK-I is a cryogenic instrument to be installed on one of the Very Large Telescope Nasmyth foci. It employs a catadioptric design and the focal plane is equipped with a mosaic of four HAWAII 2 RG arrays. Two filter wheels allow to insert broad band and narrow band filters. The instrument is designed to remain compatible with an adaptive secondary system under study for the VLT.

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We compare the redshifts of neutral carbon and carbon monoxide in the redshifted sources in which the 3 P 1 → 3 P 0 fine structure transition of neutral carbon, [C i], has been detected, in order to measure space-time variation of the fundamental constants. Comparison with the CO rotational lines measures F ≡ α 2 /μ, where α is the fine structure constant and μ is the electron-proton mass ratio, which is the same combination of constants obtained from the comparison 2 P 3/2 → 2 P 1/2 fine structure line of singly ionised carbon, [C ii]. However, neutral carbon has the distinct advantage that it may be spatially coincident with the carbon monoxide, whereas [C ii] could be located in the diffuse medium between molecular clouds, and so any comparison with CO could be dominated by intrinsic velocity differences. Using [C i], we obtain a mean variation of ΔF/F = (−3.6 ± 8.5) × 10 −5 , over z = 2.3−4.1, for the eight [C i] systems, which degrades to (−1.5± 11)× 10 −5 , over z = 2.3−6.4 when the two [C ii] systems are included. That is, zero variation over look-back times of 10.8−12.8 Gyr. However, the latest optical results indicate a spatial variation in α, where Δα/α describes a dipole and we see the same direction in ΔF/F. This trend is, however, due to a single source for which the [C i] spectrum is of poor quality. This also applies to one of the two [C ii] spectra previously used to find a zero variation in α 2 /μ. Quantifying this, we find an anti-correlation between |ΔF/F| and the quality of the carbon detection, as measured by the spectral resolution, indicating that the typical values of 50 km s −1 , used to obtain a detection, are too coarse to reliably measure changes in the constants. From the fluxes of the known z 1 CO systems, we predict that current instruments are incapable of the sensitivities required to measure changes in the constants through the comparison of CO and carbon lines. We therefore discuss in detail the use of ALMA for such an undertaking and find that, based upon the current CO detections only, the Full Array configuration is expected to detect ∼100 galaxies in [C i] at better than 10 km s −1 spectral resolution, while potentially resolving the individual molecular cloud complexes at redshifts of z 3. This could provide 1000 individual systems with which to obtain accurate measurements of space-time variation of the constants at look-back times in excess of 11 Gyr.