High-precision limit on variation in the fine-structure constant from a single quasar absorption system

Understand

The brightest southern quasar above redshift $z=1$, HE 0515$-$4414, with its strong intervening metal absorption-line system at $z_{abs}=1.1508$, provides a unique opportunity to precisely measure or limit relative variations in the fine-structure constant ($\Delta\alpha/\alpha$).

• A variation of just $\sim$3 parts per million (ppm) would produce detectable velocity shifts between its many strong metal transitions.
• Using new and archival observations from the Ultraviolet and Visual Echelle Spectrograph (UVES) we obtain an extremely high signal-to-noise ratio spectrum (peaking at S/N $\approx250$ pix$^{-1}$).
• This provides the most precise measurement of $\Delta\alpha/\alpha$ from a single absorption system to date, $\Delta\alpha/\alpha=-1.42\pm0.55_{\rm stat}\pm0.65_{\rm sys}$ ppm, comparable with the precision from previous, large samples of $\sim$150 absorbers.