Constraining the variation in the fine-structure constant using SDSS DR7 quasi-stellar object spectra

Abstract

We report on a robust constraint on the possible variation of the fine-structure constant, α≡ e2/h{stroke}c, obtained using OIII λλ 4959,5007 nebular emission lines from quasi-stellar objects (QSOs). We find Δα/α = -(2.1 ± 1.6) × 10-5, based on a well-selected sample of 2347 QSOs from the Sloan Digital Sky Survey Data Release 7 with 0.02 < z < 0.74. Our result is consistent with a non-varying a at a level of 2 × 10-5 over approximately 7 Gyr. This is the largest sample of extragalactic objects yet used to constrain the variation of α. While this constraint is not as stringent as those determined using the many-multiplet method, it is free from various systematic effects. A factor of ~4 improvement in Δα/α achieved here compared to a previous study is consistent with what is expected based on the sample used here, which is a factor of 14 times larger. This suggests that errors are mainly dominated by statistical uncertainty. We also find that the ratio of transition probabilities corresponding to the OIII λ5007 and λ4959 lines is 2.933 ± 0.002, in good agreement with the measurements of the National Institute of Standards and Technology. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.