Abstract
Investigating the use of the Hubble diagram to measure the cosmological constant ( Lambda ) and the mass density of the Universe ( OmegaM() ), we found an important focusing effect in Lambda for z ~ 3. This effect implies that the apparent magnitude of a standard candle at z = 2-3 has almost no dependence on Lambda for OmegaM() > 0.2 and that OmegaM() can be measured independently of Omega_Λ() by targeting the z range according to an estimate of the value of OmegaM() . We explore the evidence in support of the suggestion that extreme starburst galaxies (H IIG) can be used as distance estimators up to high redshifts. We have compiled literature data of H IIG up to z ~ 3 and found a good correlation (in spite of systematic effects such as age, extinction, kinematics, and metallicity) between their luminosity and velocity dispersion measured from their strong emission lines, thus confirming the correlation already known to exist for H IIG in the nearby Universe.
