| Authors | Freedman, Wendy L.; Burns, Christopher R.; Phillips, M. M.; Wyatt, Pamela; Persson, S. E.; Madore, Barry F.; Contreras, Carlos; Folatelli, Gaston; Gonzalez, E. Sergio; Hamuy, Mario; Hsiao, Eric; Kelson, Daniel D.; Morrell, Nidia; Murphy, D. C.; Roth, Miguel; Stritzinger, Maximilian; Sturch, Laura; Suntzeff, Nick B.; Astier, P.; Balland, C.; Bassett, Bruce; Boldt, Luis; Carlberg, R. G.; Conley, Alexander J.; Frieman, Joshua A.; Garnavich, Peter M.; Guy, J.; Hardin, D.; Howell, D. Andrew; Kessler, Richard; Lampeitl, Hubert; Marriner, John; Pain, R.; Perrett, Kathy; Regnault, N.; Riess, Adam G.; Sako, Masao; Schneider, Donald P.; Sullivan, Mark; Wood-Vasey, Michael |
| Abstract | The Carnegie Supernova Project (CSP) is designed to measure the luminosity distance for Type Ia supernovae (SNe Ia) as a function of redshift, and to set observational constraints on the dark energy contribution to the total energy content of the universe. The CSP differs from other projects to date in its goal of providing an I-band rest-frame Hubble diagram. Here, we present the first results from near-infrared observations obtained using the Magellan Baade telescope for SNe Ia with 0.1 m = 0.27 ± 0.02(statistical) and ΩDE = 0.76 ± 0.13(statistical) ± 0.09(systematic), for the matter and dark energy densities, respectively. If we parameterize the data in terms of an equation of state, w (with no time dependence), assume a flat geometry, and combine with baryon acoustic oscillations, we find that w = -1.05 ± 0.13(statistical) ± 0.09(systematic). The largest source of systematic uncertainty on w arises from uncertainties in the photometric calibration, signaling the importance of securing more accurate photometric calibrations for future supernova cosmology programs. Finally, we conclude that either the dust affecting the luminosities of SNe Ia has a different extinction law (RV = 1.8) than that in the Milky Way (where RV = 3.1), or that there is an additional intrinsic color term with luminosity for SNe Ia, independent of the decline rate. Understanding and disentangling these effects is critical for minimizing the systematic uncertainties in future SN Ia cosmology studies. This paper includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile. |
