A Measurement of the Rate of Type Ia Supernovae at Redshift z ≈ 0.1 from the First Season of the SDSS-II Supernova Survey
We present a measurement of the rate of Type Ia supernovae (SNe Ia) from the first of three seasons of data from the SDSS-II Supernova Survey. For this measurement, we include 17 SNe Ia at redshift z <= 0.12. Assuming a flat cosmology with Ωm = 0.3 = 1 - ΩΛ, we find a volumetric SN Ia rate of [ 2.93+ 0.17-0.04(systematic)+ 0.90-0.71(statistical) ] × 10-5 SNe Mpc -3 h370 yr -1, at a volume-weighted mean redshift of 0.09. This result is consistent with previous measurements of the SN Ia rate in a similar redshift range. The systematic errors are well controlled, resulting in the most precise measurement of the SN Ia rate in this redshift range. We use a maximum likelihood method to fit SN rate models to the SDSS-II Supernova Survey data in combination with other rate measurements, thereby constraining models for the redshift evolution of the SN Ia rate. Fitting the combined data to a simple power-law evolution of the volumetric SN Ia rate, rV propto (1 + z)β, we obtain a value of β = 1.5 +/- 0.6, i.e., the SN Ia rate is determined to be an increasing function of redshift at the ~2.5 σ level. Fitting the results to a model in which the volumetric SN rate is rV = Aρ(t) + Bdot rho(t), where ρ (t) is the stellar mass density and dot rho(t) is the star formation rate, we find A = (2.8 +/- 1.2) × 10-14 SNe M-1⊙ yr -1, B = (9.3+ 3.4-3.1) × 10-4 SNe M-1⊙.