Redshift drift cosmography with ELT and SKAO measurements

Mapping the expansion history of the universe is a compelling task of physical cosmology, especially in the context of the observational evidence for the recent acceleration of the universe, which demonstrates that canonical theories of cosmology and particle physics are incomplete and that there is new physics still to be discovered. Cosmography is a phenomenological approach to cosmology, where (with some caveats) physical quantities are expanded as a Taylor series in the cosmological redshift z, or analogous parameters such as the resealed redshift y = z/(1 + z) or the logarithmic redshift x = In (1 + z). Moreover, the redshift drift of objects following cosmological expansion provides a model-independent observable, detectable by facilities currently under construction, viz. the Extremely Large Telescope and the Square Kilometre Array Observatory (at least in its full configuration). Here, we use simulated redshift drift measurements from the two facilities to carry out an assessment of the cosmological impact and model discriminating power of redshift drift cosmography. We find that the combination of measurements from the two facilities can provide a stringent test of the A cold dark matter paradigm, and that overall the logarithmic-based expansions of the spectroscopic velocity drift are the most reliable ones, performing better than analogous expansions in the redshift or the resealed redshift: the former nominally gives the smaller error bars for the cosmographic coefficients but is vulnerable to biases in the higher order terms (in other words, it is only reliable at low redshifts), while the latter always performs poorly.

Automated summary

Mapping the expansion history of the universe is an important task that can reveal the deficiencies in current cosmological and particle physics theories. Cosmography is a phenomenological approach that expands physical quantities using parameters such as redshift or logarithmic redshift. The redshift drift, measured by upcoming facilities, can provide valuable insight into cosmological models. By analyzing simulated redshift drift measurements, this study finds that the logarithmic-based expansions of spectroscopic velocity drift are the most reliable and can provide a stringent test for dark matter paradigms.