EDP Sciences
Free access
Volume 434, Number 2, May I 2005
Page(s) 543 - 552
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20041738

A&A 434, 543-552 (2005)
DOI: 10.1051/0004-6361:20041738

Can hidden correlations mimic a variable fine structure constant?

R. Bandiera1 and E. Corbelli2

1  INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
    e-mail: bandiera@arcetri.astro.it
2  INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
    e-mail: edvige@arcetri.astro.it

(Received 27 July 2004 / Accepted 20 December 2004)

Murphy et al. (2003a, MNRAS, 345, 609) claim to find evidence of cosmological variations of the fine structure constant $\alpha$ in the spectra of intervening QSO absorption line systems. We find that this result is affected by systematic effects. The $\alpha$ values estimated in individual line systems depend on the set of atomic transitions used and therefore the quoted dependence on the cosmic age may reflect the fact that different sets of transitions are used at different redshifts. A correlation between line shifts and relative optical depths of the atomic transitions is also present. This correlation is very tight for a high-redshift subsample and accounts for the anomalous dispersion of the $\alpha$ values found by Murphy et al. (2003a) in this subsample. The above correlations are consistent with a scenario in which gravitational redshift, caused by the gravity of the dark halo, contributes to the shift in frequency of individual components. Gravitational redshift causes differential spectral shifts of the same order as magnitude of those measured. In the presence of line misidentification, these shifts can be interpreted in terms of a variable $\alpha$. In order to verify the gravitational redshift hypothesis, a direct access to Murphy et al. (2003a) data, or to a large amount of new high resolution data, is necessary.

Key words: quasars: absorption lines -- galaxies: halos -- cosmology: miscellaneous

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