The High-Z Supernova Search: Measuring cosmic deceleration and global curvature of the universe using Type IA supernovae

The High-Z Supernova Search is an international collaboration to discover a nd monitor Type Ia supernovae (SNe Ia) at z > 0.2 with the aim of measuring cosmic deceleration and global curvature. Our collaboration has pursued a basic understanding of supernovae in the nearby universe, discovering and o bserving a large sample of objects and developing methods to measure accura te distances with SNe Ia. This paper describes the extension of this progra m to z greater than or equal to 0.2, outlining our search techniques and fo llow-up program. We have devised high-throughput filters that provide accur ate two-color rest frame B and V light curves of SNe Ia, enabling us to pro duce precise, extinction-corrected luminosity distances in the range 0.25 < z < 0.55. Sources of systematic error from K-corrections, extinction, sele ction effects, and evolution are investigated, and their effects estimated. We present photometric and spectral observations of SN 1995K, our program' s first supernova (SN) and use the data to obtain a precise measurement of the luminosity distance to the z = 0.479 host galaxy. This object, when com bined with a nearby sample of SNe, yields an estimate for the matter densit y of the universe of Omega(M) = -0.2(-0.8)(+1.0) if Omega(Lambda) = 0. For a spatially flat universe composed of normal matter and a cosmological cons tant, we find Omega(M) = 0.4(-0.4)(+0.5), Omega(Lambda) = 0.6(-0.5)(+0.4). We demonstrate that with a sample of similar to 30 objects, are should be a ble to determine relative luminosity distances over the range 0 < z < 0.5 w ith sufficient precision to measure Omega(M) with an uncertainty of +/-0.2.