Monitoring the redshift-drift of the Lyman-α forest – a direct measurement of the dynamical evolution of the Universe


    L. Pasquini


    We propose to monitor the redshift drift of the Ly α forest and associated metal lines towards a sample of 20 very bright QSOs in the redshift range 2 < z < 4.2 with the ultra-stable high-resolution optical spectrograph on the E-ELT over a period of 15 yr (with observations spread over 8 yr). The redshift drift is sensitive to the difference of the expansion rate today and the expansion rate at the redshift of the absorbing structures and is directly related to the de- or acceleration of the Universe. With the proposed observations we can achieve an overall measurement accuracy of 3.5 cm/s. By monitoring the drift of the Ly α forest over a wide redshift range we will measure the instantaneous expansion rate of the Universe today and the expansion rate at high redshift. The measurement of the expansion rate and its evolution at high redshift will be an important test of General Relativity. The measurement of the instantaneous expansion rate will test whether the Universe expands today at the rate expected from other observations which, generally, measure the expansion rate averaged over a hundred Myr or more. The observations proposed can be used as a first epoch measurement for more accurate measurements by a future generation of astronomers and will thus represent a long-lasting legacy. The acquired spectra will also represent a unique resource for a wide range of other QSO absorption line studies.

    Full proposal



    Section 18 of the DRM report


    Various data accompanying the report, including examples of simulations.

    Related presentations

    DRM update, J. Liske at SWG meeting, 09 Oct 2007
    Science case, M. Haehnelt at SWG DRM workshop, 29-30 May 2007

    Related publications