Abstract

Aims. We probe the evolution of the fine-structure constant ? with cosmic time. Methods. Accurate positions of the Fe II lines ?1608, ?2382, and ?2600 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 ? Measurement (SIDAM) procedure and the ?? 2 method are used to set constraints on ??/?. Results. We have found a relative radial velocity shift between the ?1608 and ??2382, 2600 lines of ?v = -180 ±85 m s -1 (both random and systematic errors are included), which, if real, would correspond to ??/? = (5.4 ± 2.5) × 10 -6 (1? 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.