Aims. We investigate the degree of improvement in dark energy constraints
that can be achieved by extending Type Ia Supernova (SN Ia) samples to
redshifts z > 1.5 with the Hubble Space Telescope (HST), particularly in the
ongoing CANDELS and CLASH multi-cycle treasury programs.
Methods. Using the popular CPL parametrization of the dark energy, w = w0
+wa(1-a), we generate mock SN Ia samples that can be projected out to higher
redshifts. The synthetic datasets thus generated are fitted to the CPL model,
and we evaluate the improvement that a high-z sample can add in terms of
ameliorating the statistical and systematic uncertainties on cosmological
parameters.
Results. In an optimistic but still very achievable scenario, we find that
extending the HST sample beyond CANDELS+CLASH to reach a total of 28 SN Ia at z
> 1.0 could improve the uncertainty in the wa parameter by up to 21%. The
corresponding improvement in the figure of merit (FoM) would be as high as 28%.
Finally, we consider the use of high-redshift SN Ia samples to detect
non-cosmological evolution in SN Ia luminosities with redshift, finding that
such tests could be undertaken by future spacebased infrared surveys using the
James Webb Space Telescope (JWST).Comment: 9 pages, 6 figures, accepted for publication on Astronomy &
Astrophysic
