Misc,
A unified explanation for the supernova rate-galaxy mass dependency based on supernovae discovered in Sloan galaxy spectra
(Dec 26, 2014)
Abstract
Using a method to discover and classify supernovae (SNe) in galaxy spectra,
we detect 91 Type Ia SNe (SNe Ia) and 16 Type II SNe (SNe II) among \~740,000
galaxies of all types and \~215,000 star-forming galaxies without active
galactic nuclei, respectively, in Data Release 9 of the Sloan Digital Sky
Survey. Of these SNe, 22 SNe Ia and 8 SNe II are new discoveries reported here
for the first time. We use our SN samples to measure SN rates per unit mass as
a function of galaxy stellar mass, star-formation rate (SFR), and specific SFR
(sSFR), as derived by the MPA-JHU Galspec pipeline. We confirm the rate-mass
correlations, first discovered by the Lick Observatory Supernova Search, for
both SNe Ia and SNe II at median redshifts of \~0.1 and \~0.075, respectively.
The mass-normalized SN Ia and SN II rates, averaged over all masses and
redshifts in their respective galaxy samples, are 0.10 +/- 0.01 (stat) +/- 0.01
(sys) X 10^-12 Msol^-1 yr^-1 and 0.52 +0.16 -0.13 (stat) +0.02 -0.05 (sys) X
10^-12 Msol^-1 yr^-1, respectively. We convert the latter into a volumetric SN
II rate at z=0.075 of 0.621 +0.197 -0.154 (stat) +0.024 -0.063 (sys) X 10^-4
yr^-1 Mpc^-3. Assuming that SNe IIP and IIL account for 60 per cent of all CC
SNe, the volumetric CC SN rate is 1.04 +0.33 -0.26 (stat) +0.04 -0.11 (sys) X
10^-4 yr^-1 Mpc^-3. The mass-normalized SN rates also follow "rate-SFR" and
"rate-sSFR" correlations. We show that the correlations between SN Ia and SN II
rates per unit mass and stellar mass, SFR, and sSFR can be explained by a
combination of the respective SN delay-time distributions, the ages of the
surveyed galaxies, the redshifts at which they are observed, and their
star-formation histories. This model was first suggested by Kistler et al. for
the SN Ia rate-mass correlation, but is expanded here to SNe II and to
correlations with galaxy SFR and sSFR (abridged).
