Supernova Ia and galaxy cluster gas mass fraction constraints on dark energy

We use the Riess et al. (2004)(1) supernova Ia apparent magnitude versus redshift data and the Allen et al. (2004)(2) galaxy cluster gas mass fraction versus redshift data to constrain dark energy models. These data provide complementary constraints that when combined together significantly restrict model parameters and favor slowly-evolving dark energy density models, close to the Einstein cosmological constant limit of dark energy.