Classifications of the Host Galaxies of Supernovae, Set II

Abstract

Classifications on the DDO system are given for an additional 231 host galaxies of supernovae that have been discovered during the course of the Lick Observatory Supernova Search with the Katzman Automatic Imaging Telescope (KAIT). This brings the total number of hosts of supernovae (SNe) discovered (or independently rediscovered) by KAIT, which have so far been classified on a homogeneous system, to 408. The probability that SNe Ia and SNe II have a different distribution of host‐galaxy Hubble types is found to be 99.7%. A significant difference is also found between the distributions of the host galaxies of SNe Ia and of SNe Ibc (defined here to include SNe Ib, Ib/c, and Ic). However, no significant difference is detected between the frequency distributions of the host galaxies of SNe II and SNe IIn. This suggests that SNe IIn are generally not SNe Ia embedded in circumstellar material that are masquerading as SNe II. Furthermore, no significant difference is found between the distribution of the Hubble types of the hosts of SNe Ibc and of SNe II. Additionally, SNe II‐P and SNe II‐L are found to occur among similar stellar populations. The ratio of the number of SNe Ia‐pec to normal SNe Ia appears to be higher in early‐type galaxies than it is in galaxies of later morphological types. This suggests that the ancestors of SNe Ia‐pec may differ systematically in age or composition from the progenitors of normal SNe Ia. Unexpectedly, five SNe of Types Ib/c, II, and IIn (all of which are thought to have massive progenitors) are found in host galaxies that are nominally classified as types E and S0. However, in each case the galaxy classification is uncertain, or newly inspected images show evidence suggesting a later classification. Among these five objects, NGC 3720, the host galaxy of SN 2002at, was apparently misidentified in the Carnegie Atlas of Galaxies.