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 (SNe). Simulating observed samples of Type Ia and mixed Type Ibc/Ia populations at a range of redshifts for an underlying cosmological concordance model (ΩM = 0.27, Ωλ = 0.73), we find that even small contamination levels, 2%-5%, may bias the derived Ωλ and ΩM toward 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 of Kim and coworkers, but include Type Ibc contamination. For this distribution we illustrate the effect of Type Ibc contamination on the distance modulus versus redshift diagram for low- and high-precision measurements.