The High-Z Supernova Search: Measuring Cosmic Deceleration and Global Cur vature of the Universe Using Type Ia Supernovae

Abstract

The High-Z Supernova Search is an international collaboration to discover and monitor type Ia supernovae (SN 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 observing a large sample of objects, and developing methods to measure accurate distances with SN Ia. This paper describes the extension of this program to $z\ge 0.2$, outlining our search techniques and follow-up program. We have devised high-throughput filters which provide accurate two-color restframe $B$ and $V$ light curves of SN Ia, enabling us to produce precise, extinction-corrected luminosity distances in the range $0.25<z<0.55$. Sources of systematic error from K-corrections, extinction, selection effects, and evolution are investigated, and their effects estimated. We present photometric and spectral observations of SN 1995K, our program's first supernova, and use the data to obtain a precise measurement of the luminosity distance to the $z=0.479$ host galaxy. This object, when combined with a nearby sample of SN, yields an estimate for the matter density of the Universe of $\hat{I}{\text{c◯}}_M=-0.2_{-0.8}^{+1.0}$ if $\hat{I}{\text{c◯}}_{\hat{I}}›=0$. For a spatially flat universe composed of normal matter and a cosmological constant, we find $\hat{I}{\text{c◯}}_M=0.4_{-0.4}^{+0.5}$, $\hat{I}{\text{c◯}}_{\hat{I}}›=0.6_{-0.5}^{+0.4}$. We demonstrate that with a sample of $\sim 30$ objects, we should be able to determine relative luminosity distances over the range $0<z<0.5$ with sufficient precision to measure $\hat{I}{\text{c◯}}_M$ with an uncertainty of $\pm 0.2$.

51 pages, 14 figures, To Appear in the Astrophysical Journal