Further evidence for a variable finestructure constant from Keck/HIRES QSO absorption spectra
Abstract
We have previously presented evidence for a varying finestructure constant, α, in two independent samples of Keck/HIRES quasistellar object (QSO) absorption spectra. Here we present a detailed manymultiplet analysis of a third Keck/HIRES sample containing 78 absorption systems. We also reanalyse 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 lowz (i.e. z_{abs} < 1.8) and highz 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 highz 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 twopoint correlation function for α is consistent with zero over 0.213 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 manymultiplet analyses of independent QSO spectra from different telescopes and spectrographs will provide a now crucial check on our Keck/HIRES results.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 October 2003
 DOI:
 10.1046/j.13658711.2003.06970.x
 arXiv:
 arXiv:astroph/0306483
 Bibcode:
 2003MNRAS.345..609M
 Keywords:

 atomic data;
 line: profiles;
 methods: laboratory;
 techniques: spectroscopic;
 quasars: absorption lines;
 ultraviolet: general;
 Astrophysics;
 General Relativity and Quantum Cosmology;
 High Energy Physics  Phenomenology
 EPrint:
 31 pages, 25 figures (29 EPS files), 8 tables. Accepted by MNRAS. Colour versions of Figs. 6, 8 &