Constraining Dark Energy with Type Ia Supernovae and Large-Scale Structure

Measurements of the distances to type Ia supernovae have produced strong evidence that the expansion of the Universe is accelerating, implying the existence of a nearly uniform component of dark energy with negative pressure. We show that constraints to this mysterious component based upon large-scale structure nicely complement the SN Ia data, and that together they require ${\Omega }_X={\rho }_X/{\rho }_{\mathrm{crit}}\in (0.6,0.7)$ and ${w=p}_X/{\rho }_X<-0.6\mathrm{}$ ( $95\%$ C.L.), for the favored flat Universe. Other cosmological data support this conclusion. The simplest explanation, a cosmological constant, is consistent with this, while some of the other possibilities are not.