The Effect of Type Ibc Contamination in Cosmological Supernova Samples

We explore the effect of contamination of intermediate redshift Type Ia supernova samples by Type Ibc supernovae. Simulating observed samples of Ia and mixed Ibc/Ia populations at a range of redshifts for an underlying cosmological concordance model (\Omega_{m}=0.27, \Omega_{\Lambda}=0.73), we find that even small contamination levels, 2-5% may bias the derived \Omega_{\Lambda} and \Omega_{m} towards larger values. We thus emphasize the need for clean samples of Type Ia SNe for accurate measurements of the cosmological parameters. We also simulate a SN sample similar to the fiducial SNAP detected distribution (Kim et al. 2004), but include Ibc contamination. For this distribution we illustrate the effect of Ibc contamination on the distance modulus vs. redshift diagram for low and high precision measurements.