Open AccessFurther evidence for a variable fine‐structure constant from Keck/HIRES QSO absorption spectra
Author(s) -
Murphy M. T.,
Webb J. K.,
Flambaum V. V.
Publication year - 2003
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2003.06970.x
Subject(s) - physics , astrophysics , redshift , multiplet , spectral line , quasar , absorption (acoustics) , absorption spectroscopy , spectroscopy , galaxy , optics , astronomy
We have previously presented evidence for a varying fine‐structure constant, α, in two independent samples of Keck/HIRES quasi‐stellar object (QSO) absorption spectra. Here we present a detailed many‐multiplet analysis of a third Keck/HIRES sample containing 78 absorption systems. We also re‐analyse the previous samples, providing a total of 128 absorption systems over the redshift range 0.2 < z abs < 3.7 . The results, with raw statistical errors, indicate a smaller weighted mean α in the absorption clouds: Δα/α= (−0.574 ± 0.102) × 10 −5 . All three samples separately yield consistent and significant values of Δα/α . The analyses of low‐ z (i.e. z abs < 1.8 ) and high‐ z systems rely on different ions and transitions with very different dependences on α, yet they also give consistent results. We identify an additional source of random error in 22 high‐ z systems characterized by transitions with a large dynamic range in apparent optical depth. Increasing the statistical errors on Δα/α for these systems gives our fiducial result, a weighted mean Δα/α= (−0.543 ± 0.116) × 10 −5 , representing 4.7σ evidence for a varying α. Assuming that Δα/α= 0 at z abs = 0 , the data marginally prefer a linear increase in α with time rather than a constant offset from the laboratory value: . The two‐point correlation function for α is consistent with zero over 0.2–13 Gpc comoving scales and the angular distribution of Δα/α shows no significant dipolar anisotropy. We therefore have no evidence for spatial variations in Δα/α . We extend our previous searches for possible systematic errors, giving detailed analyses of potential kinematic effects, line blending, wavelength miscalibration, spectrograph temperature variations, atmospheric dispersion and isotopic/hyperfine structure effects. The latter two are potentially the most significant. However, overall, known systematic errors do not explain the results. Future many‐multiplet analyses of independent QSO spectra from different telescopes and spectrographs will provide a now crucial check on our Keck/HIRES results.