Abstract

Aims. We probe the evolution of the fine-structure constant α with cosmic time. Methods. Accurate positions of the Fe II lines λ1608, λ2382, and λ2600 are measured in the zabs = 1.84 absorption system from a high-resolution (FWHM ∼ 3.8 km s-1) and high signal-to-noise (S/N ≳ 100) spectrum of the quasar Q 1101-264 (z em = 2.15, V = 16.0), integrated for 15.4 h. The Single Ion Differential α Measurement (SIDAM) procedure and the ΔΧ 2 method are used to set constraints on Δα/α. Results. We have found a relative radial velocity shift between the λ1608 and λλ2382, 2600 lines of Δv = -180 ±85 m s -1 (both random and systematic errors are included), which, if real, would correspond to Δα/α = (5.4 ± 2.5) × 10 -6 (1σ C.L.). Considering the strong implications of a such variability, additional observations with comparable accuracy at redshift z ∼ 1.8 are required to confirm this result. © ESO 2007.