Quasars: Standard Candles up to z = 7.5 with the Precision of Supernovae Ia

Currently, the Λ cold dark matter model, which relies on the existence of cold dark matter and a cosmological constant Λ, best describes the universe. However, we lack information in the high-redshift ( z ) region between Type Ia supernovae (SNe Ia; up to z = 2.26) and the cosmic microwave background ( z = 1100), an interval crucial to test cosmological models and their possible evolution. We have defined a sample of 983 quasars up to z = 7.54 with a reduced intrinsic dispersion δ = 0.007, which determines the matter density parameter Ω M with the same precision of SNe Ia. Although previous analysis have used quasars as cosmological tools, this is the first time that high-redshift sources, in this case quasars, as standalone cosmological probes yield such tight constraints on Ω M . Our results show the importance of correcting cosmological relationships for selection biases and redshift evolution and how the choice of a golden sample reduces considerably the intrinsic scatter. This proves the reliability of quasars as standard cosmological candles.