Determining the equation of state of dark energy from angular size of compact radio sources and X-ray gas mass fraction of galaxy clusters

Using recent measurements of angular size of high-z milliarcsecond compact radio Sources compiled by Gurvits et al. (1999) and X-ray gas mass fraction of galaxy clusters published by Allen et al. (2002, 2003), we explore their bounds on the equation of state, omega(x)equivalent top(x)/rho(x), of the dark energy, whose existence has been congruously Suggested by various cosmological observations. We relax the usual constraint omega(x)greater than or equal to-1, and find that combining the two databases yields a nontrivial lower bound on omega(x). Under the assumption of a flat universe, we obtain a bound -2.22<omega(x)<-0.62 at 95.4% confidence level. The 95.4% confidence bound goes to -1 <=omega(x)<-0.60 when the constraint omega(x)>=-1 is imposed.