Toward a direct measurement of the cosmic acceleration: roadmap and forecast on FAST

Understand

HI absorption systems are great targets for direct measurement of the Sandage-Loeb (SL) effect throughout a wide range of redshift for ground-based radio telescopes.

• We demonstrate the significance of improving the accuracy of SL effect measurement in cosmological model selection.
• With its wide sky coverage and high sensitivity, we forecast that for 1 year of the upcoming commensal survey (CRAFTS) the FAST telescope is capable of discovering about 800 HI absorption systems thereby improving the SL measurement accuracy.
• Aiming to measurement the cosmic redshift drift rate at the precision of $\dot{z} \sim 10^{-10} \mathrm{decade^{-1}}$, we propose combined observation mode with blind-searching and targeted observation.