Forecasting cosmic acceleration measurements using the Lyman-α forest

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Abstract
We present results from end-to-end simulations of observations designed to constrain the rate of change in the expansion history of the Universe using the redshift drift of the Lyman-α forest absorption lines along the lines of sight towards bright quasars. For our simulations, we take Lyman-α forest lines extracted from Keck/HIRES spectra of bright quasars at z > 3, and compare the results from these real quasar spectra with mock spectra generated via Monte Carlo realizations. We use the results of these simulations to assess the potential for a dedicated observatory to detect redshift drift, and quantify the telescope and spectrograph requirements for these observations. Relative to Liske et al. ( 2008), two main refinements in the current work are inclusion of quasars from more recent catalogs and consideration of a realistic observing strategy for a dedicated redshift drift experiment that maximizes |$\dot{v}/\sigma _{\dot{v}}$|⁠. We find that using a dedicated facility and our designed observing plan, the redshift drift can be detected at 3σ significance in 15 yr with a 25 m telescope, given a spectrograph with long-term stability with R = 50 000 and 25 per cent total system efficiency. To achieve this significance, the optimal number of targets is four quasars, with observing time weighted based upon |$\dot{v}/\sigma _{\dot{v}}$| and object visibility. This optimized strategy leads to a 9 per cent decrease in the telescope diameter or a 6 per cent decrease in the required time to achieve the same S/N as for the idealized case of uniformly distributing time to the same quasars.
Funding Information
  • NASA Exoplanet Science Institute
  • National Aeronautics and Space Administration

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