The redshifts of all cosmologically distant sources are expected to experience a small, systematic drift as a function of time due to the evolution of the Universe's expansion rate. A measurement of this effect would represent a direct and entirely model-independent determination of the expansion history of the Universe over a redshift range that is inaccessible to other methods. Here we investigate the impact of the next generation of Extremely Large Telescopes on the feasibility of detecting and characterising the cosmological redshift drift. We consider the Lyman alpha forest in the redshift range 2 < z < 5 and other absorption lines in the spectra of high redshift QSOs as the most suitable targets for a redshift drift experiment. Assuming photon-noise limited observations and using extensive Monte Carlo simulations we determine the accuracy to which the redshift drift can be measured from the Ly alpha forest as a function of signal-to-noise and redshift. Based on this relation and using the brightness and redshift distributions of known QSOs we find that a 42-m telescope is capable of unambiguously detecting the redshift drift over a period of ~20 yr using 4000 h of observing time. Such an experiment would provide independent evidence for the existence of dark energy without assuming spatial flatness, using any other cosmological constraints or making any other astrophysical assumption.Comment: Accepted for publication in MNRAS, 27 pages, 19 figure

Abstract.We assess the cosmological variability of the fine-structure constant α from the analysis of an ensemble of Fe  λ1608, λ2344, λ2374, λ2383, λ2587, and λ2600 absorption lines at the redshift z = 1.15 toward the QSO HE 0515-4414 by means of the standard many-multiplet (MM) technique and its revision based on linear regression (RMM). This is the first time the MM technique is applied to exceptional high-resolution and high signal-to-noise QSO spectra recorded with the UV-Visual Echelle Spectrograph (UVES) at the ESO Very Large Telescope (VLT). Our analysis results in ∆α/α MM = (0.1 ± 1.7) × 10and ∆α/α RMM = (−0.4 ± 1.9 ± 2.7 sys ) × 10 −6 , which are the most stringent bounds hitherto infered from an individual QSO absorption system. Our results support the null hypothesis ∆α/α = 0 at a significance level of 91 percent, whereas the support for the result ∆α/α = −5.7 × 10 −6 presented in former MM studies is 12 percent.

Context. Absorption-line systems detected in quasar spectra can be used to compare the value of the fine-structure constant, α, measured today on Earth with its value in distant galaxies. In recent years, some evidence has emerged of small temporal and also spatial variations in α on cosmological scales. These variations may reach a fractional level of ≈10 ppm (parts per million). Aims. To test these claims we are conducting a Large Program of observations with the Very Large Telescope's Ultraviolet and Visual Echelle Spectrograph (UVES), and are obtaining high-resolution (R ≈ 60 000) and high signal-to-noise ratio (S /N ≈ 100) UVES spectra calibrated specifically for this purpose. Here we analyse the first complete quasar spectrum from this programme, that of HE 2217−2818. Methods. We applied the many multiplet method to measure α in five absorption systems towards this quasar: z abs = 0.7866, 0.9424, 1.5558, 1.6279 , and 1.6919. Results. The most precise result is obtained for the absorber at z abs = 1.6919 where 3 Fe  transitions and Al  λ1670 have high S/N and provide a wide range of sensitivities to α. The absorption profile is complex with several very narrow features, and it requires 32 velocity components to be fitted to the data. We also conducted a range of tests to estimate the systematic error budget. Our final result for the relative variation in α in this system is ∆α/α = +1.3 ± 2.4 stat ± 1.0 sys ppm. This is one of the tightest current bounds on α-variation from an individual absorber. A second, separate approach to the data reduction, calibration, and analysis of this system yielded a slightly different result of −3.8 ± 2.1 stat ppm, possibly suggesting a larger systematic error component than our tests indicated. This approach used an additional 3 Fe  transitions, parts of which were masked due to contamination by telluric features. Restricting this analysis to the Fe  transitions alone and using a modified absorption profile model gave a result that is consistent with the first approach, ∆α/α = +1.1 ± 2.6 stat ppm. The four other absorbers have simpler absorption profiles, with fewer and broader features, and offer transitions with a narrower range of sensitivities to α. They therefore provide looser bounds on ∆α/α at the > ∼ 10 ppm precision level. Conclusions. The absorbers towards quasar HE 2217−2818 reveal no evidence of any variation in α at the 3-ppm precision level (1σ confidence). If the recently reported 10-ppm dipolar variation in α across the sky is correct, the expectation at this sky position is (3.2−5.4) ± 1.7 ppm depending on dipole model used. Our constraint of ∆α/α = +1.3 ± 2.4 stat ± 1.0 sys ppm is not inconsistent with this expectation.

We have detected in high resolution spectra of the quasar Q0347-3819 obtained with the UVES spectrograph at the VLT/Kueyen telescope over 80 absorption features in the Lyman and Werner H 2 bands at the redshift of a damped Lyα system at z abs = 3.025. At the same redshift, numerous absorption lines of atoms and low ions (H

Abstract. We present 4 new measurements of nitrogen abundances and one upper limit in damped Ly α absorbers (DLAs) obtained by means of high resolution (FWHM ≃ 7 km s −1 ) UVES/VLT spectra. In addition to these measurements we have compiled data from all DLAs with measurements of nitrogen and α-capture elements (O, S or Si) available in the literature, including all HIRES/Keck and UVES/VLT data for a total of 33 systems, i.e. the largest sample investigated so far. We find that [N/α]

We present an accurate analysis of the H 2 absorption lines from the z abs ∼ 2.4018 damped Lyαsystem towards HE 0027−1836 observed with the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph (VLT/UVES) as a part of the European Southern Observatory Large Programme "The UVES large programme for testing fundamental physics" to constrain the variation of proton-to-electron mass ratio, µ ≡ m p /m e . We perform cross-correlation analysis between 19 individual exposures taken over three years and the combined spectrum to check the wavelength calibration stability. We notice the presence of a possible wavelength dependent velocity drift especially in the data taken in 2012. We use available asteroids spectra taken with UVES close to our observations to confirm and quantify this effect. We consider single and two component Voigt profiles to model the observed H 2 absorption profiles. We use both linear regression analysis and Voigt profile fitting where ∆µ/µ is explicitly considered as an additional fitting parameter. The two component model is marginally favored by the statistical indicators and we get ∆µ/µ = −2.5 ± 8.1 stat ± 6.2 sys ppm. When we apply the correction to the wavelength dependent velocity drift we find ∆µ/µ = −7.6 ± 8.1 stat ± 6.3 sys ppm. It will be important to check the extent to which the velocity drift we notice in this study is present in UVES data used for previous ∆µ/µ measurements.

Abstract. We propose a new methodology for probing the cosmological variability of α from pairs of Fe  lines (SIDAM, single ion differential α 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) The fundamental photon noise limitation in the ∆α/α 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 (∆α/α ≥ 4.5 × 10 −8 ) can be achieved along cosmological distances with differential measurements of ∆α/α.

The methanol molecule CH 3 OH has a complex microwave spectrum with a large number of very strong lines. This spectrum includes purely rotational transitions as well as transitions with contributions of the internal degree of freedom associated with the hindered rotation of the OH group. The latter takes place due to the tunneling of hydrogen through the potential barriers between three equivalent potential minima. Such transitions are highly sensitive to changes in the electron-to-proton mass ratio, µ = m e /m p , and have different responses to µ-variations. The highest sensitivity is found for the mixed rotation-tunneling transitions at low frequencies. Observing methanol lines provides more stringent limits on the hypothetical variation of µ than ammonia observation with the same velocity resolution. We show that the best quality radio astronomical data on methanol maser lines constrain the variability of µ in the Milky Way at the level of |∆µ/µ| < 28 × 10 −9 (1σ) which is in line with the previously obtained ammonia result, |∆µ/µ| < 29 × 10 −9 (1σ). This estimate can be further improved if the rest frequencies of the CH 3 OH microwave lines will be measured more accurately.