Indications of a Spatial Variation of the Fine Structure Constant

Abstract

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...

The UVES Large Program for testing fundamental physics – III. Constraints on the fine-structure constant from three telescopes

“…However, amassing a large number of new observations of quasars similar in scope to Webb et al (2011) and King et al (2012) is not necessary for comprehensively checking the possible evidence for non-zero ∆α/α in those works. Instead, carefully targeting future observations and paying particular attention to (super)calibration are most important.…”

“…The most surprising ∆α/α results come from a sample of 143 Keck/HIRES-observed absorption systems (Murphy et al 2003;Murphy et al 2004) and 154 VLT/UVES-observed absorption systems (Webb et al 2011;King et al 2012). When King et al (2012) combined their VLT measurements with the Murphy et al (2004) Keck ones, they found internally consistent evidence for a dipolar variation in α across the sky.…”

Fundamental constants and high‐resolution spectroscopy

“…The main drawback of the sample assembled by Webb et al (2011) is that the observations where mainly acquired with scientific objectives other than the measurement of ∆α/α thus systematic errors are not monitored and minimised. In 2010 our Large Program of optical observations dedicated to measuring α and µ in distant galaxies was approved by the ESO Observing Programmes Committee.…”

Atomic and molecular absorption in redshifted radio sources

“…The detection of H I 21-cm is of further interest as the comparison of its redshift with that of other transitions has the potential to measure past values of the fundamental constants of nature (Tzanavaris et al 2005(Tzanavaris et al , 2007, which may exhibit a spatial (Berengut et al 2011;Webb et al 2011), as well as a tempo-ral (Murphy et al 2003) variation. Radio data can yield at least an order of magnitude in precision in the measurement of the constants over the optical data (see Curran et al 2004a).…”