A Measurement of the Rate of type-Ia Supernovae at Redshift $z\approx$ 0.1 from the First Season of the SDSS-II Supernova Survey

Abstract

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 $z\le 0.12$. Assuming a flat cosmology with $\hat{I}{\text{c◯}}_m=0.3=1-\hat{I}{\text{c◯}}_{\hat{I}}›$, we find a volumetric SN Ia rate of $[2.93_{-0.04}^{+0.17}(\mathrm{systematic}{)}_{-0.71}^{+0.90}(\mathrm{statistical})]\times 10^{-5}\mathrm{SNe}{\mathrm{Mpc}}^{-3}{h}_{70}^3{\mathrm{year}}^{-1}$, 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, $r_V\propto (1+z{)}^2$, we obtain a value of ${\hat{I}}^2=1.5\pm 0.6$, i.e. the SN Ia rate is determined to be an increasing function of redshift at the $\sim 2.5\ddot{I}ƒ$ level. Fitting the results to a model in which the volumetric SN rate, $r_V=A\ddot{I}(t)+B\dot{\ddot{I}}(t)$, where $\ddot{I}(t)$ is the stellar mass density and $\dot{\ddot{I}}(t)$ is the star formation rate, we find $A = (2.8 \pm 1.2) \times 10^{-14} \mathrm{SNe} \mathrm{M}_{\sun}^{-1} \mathrm{year}^{-1}$, $B = (9.3^{+3.4}_{-3.1})\times 10^{-4} \mathrm{SNe} \mathrm{M}_{\sun}^{-1}$.

65 pages, 12 figures