On The Rates Of Type Ia Supernovae In Dwarf And Giant Hosts With ROTSE-IIIb

Quimby, Robert M.
Yuan, Fang
Akerlof, Carl
Wheeler, J. Craig
Warren, Michael S.
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We present a sample of 23 spectroscopically confirmed Type Ia supernovae (SNe Ia) that were discovered in the background of galaxy clusters targeted by ROTSE-IIIb and use up to 18 of these to determine the local ((z) over bar = 0.05) volumetric rate. Since our survey is flux limited and thus biased against fainter objects, the pseudo-absolute magnitude distribution (pAMD) of SNe Ia in a given volume is an important concern, especially the relative frequency of high-to low-luminosity SNe Ia. We find that the pAMD derived from the volume-limited Lick Observatory Supernova Search (LOSS) sample is incompatible with the distribution of SNe Ia in a volume-limited (z < 0.12) sub-sample of the Sloan Digital Sky Survey II (SDSS-II). The LOSS sample requires far more low-luminosity SNe Ia than the SDSS-II can accommodate. Even though LOSS and SDSS-II have sampled different SNe Ia populations, their volumetric rates are surprisingly similar. Using the same model pAMD adopted in the SDSS-II SNe Ia rate calculation and excluding two high-luminosity SNe Ia from our sample, we derive a rate that is marginally higher than previous low-redshift determinations. With our full sample and the LOSS pAMD, our rate is more than double the canonical value. We also find that 5 of our 18 SNe Ia are hosted by very low luminosity (M-B > -16) galaxies, whereas only 1 out of 79 nearby SDSS-II SNe Ia have such faint hosts. It is possible that previous works have undercounted either low-luminosity SNe Ia, SNe Ia in low-luminosity hosts, or peculiar SNe Ia (sometimes explicitly), and the total SNe Ia rate may be higher than the canonical value.

Quimby, Robert M., Fang Yuan, Carl Akerlof, J. Craig Wheeler, and Michael S. Warren. >On the Rates of Type Ia Supernovae in Dwarf and Giant Hosts with ROTSE-IIIb.> The Astronomical Journal, Vol. 144, No. 6 (Dec., 2012): 177.