Alternative High-z Cosmic Tracers and the Dark Energy Equation of State
  We propose to use alternative cosmic tracers to measure the dark energy
equation of state and the matter content of the Universe [w(z) & \Omega_m]. Our
proposed method consists of two components: (a) tracing the Hubble relation
using HII-like starburst galaxies, as an alternative to SNIa, which can be
detected up to very large redshifts, z~4, and (b) measuring the clustering
pattern of X-ray selected AGN at a median redshift of ~1. Each component of the
method can in itself provide interesting constraints on the cosmological
parameters, especially under our anticipation that we will reduce the
corresponding random and systematic errors significantly. However, by joining
their likelihood functions we will be able to put stringent cosmological
constraints and break the known degeneracies between the dark energy equation
of state (whether it is constant or variable) and the matter content of the
universe and provide a powerful and alternative rute to measure the
contribution to the global dynamics, and the equation of state, of dark energy.
A preliminary joint analysis of X-ray selected AGN (based on a small XMM
survey) and the currently largest SNIa sample (Kowalski et al 2008), provides:
Omega_m=0.28^{+0.02}_{-0.04} and w=-1.0 +-0.1.
