ABRIDGED We present measurements of the Type Ia supernova (SN) rate in galaxy clusters based on data from the Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey. The cluster SN Ia rate is determined from 9 SN events in a set of 71 C4 clusters at z <0.17 and 27 SN events in 492 maxBCG clusters at 0.1 < z < 0.3$. We find values for the cluster SN Ia rate of $({ 0.37}^{ +0.17+0.01}_{ -0.12-0.01}) \mathrm{ SNu}r h^{ 2}$ and $({ 0.55}^{ +0.13+0.02}_{ -0.11-0.01}) \mathrm{ SNu}r h^{ 2}$ ($\mathrm{ SNu}x = 10^{ -12} L_{ x\sun}^{ -1} \mathrm{ yr}^{ -1}$) in C4 and maxBCG clusters, respectively, where the quoted errors are statistical and systematic, respectively. The SN rate for early-type galaxies is found to be $({ 0.31}^{ +0.18+0.01}_{ -0.12-0.01}) \mathrm{ SNu}r h^{ 2}$ and $({ 0.49}^{ +0.15+0.02}_{ -0.11-0.01})$ $\mathrm{ SNu}r h^{ 2}$ in C4 and maxBCG clusters, respectively. The SN rate for the brightest cluster galaxies (BCG) is found to be $({ 2.04}^{ +1.99+0.07}_{ -1.11-0.04}) \mathrm{ SNu}r h^{ 2}$ and $({ 0.36}^{ +0.84+0.01}_{ -0.30-0.01}) \mathrm{ SNu}r h^{ 2}$ in C4 and maxBCG clusters. The ratio of the SN Ia rate in cluster early-type galaxies to that of the SN Ia rate in field early-type galaxies is ${ 1.94}^{ +1.31+0.043}_{ -0.91-0.015}$ and ${ 3.02}^{ +1.31+0.062}_{ -1.03-0.048}$, for C4 and maxBCG clusters. The SN rate in galaxy clusters as a function of redshift...shows only weak dependence on redshift. Combining our current measurements with previous measurements, we fit the cluster SN Ia rate data to a linear function of redshift, and find $r_{ L} = $ $[(0.49^{ +0.15}_{ -0.14}) +$ $(0.91^{ +0.85}_{ -0.81}) \times z]$ $\mathrm{ SNu}B$ $h^{ 2}$. A comparison of the radial distribution of SNe in cluster to field early-type galaxies shows possible evidence for an enhancement of the SN rate in the cores of cluster early-type galaxies... we estimate the fraction of cluster SNe that are hostless to be $(9.4^+8._3-5.1)%$.
Categories: astro-ph.CO