SUPERNOVAE AND THEIR HOST GALAXIES

摘要

We study the correlations between the distance of a supernova (SN) from the center of the host galaxy and measurable properties such as SN spectral types and luminosity at maximum light for Type Ⅰa supernovae (SNe Ⅰa). The rate of SNe Ⅰa within 1 kpc of the center of spiral galaxies is significantly lower than outside this region. The rates of Type Ⅱ (SNe Ⅱ) and Type Ⅰb/c (SNe Ⅰb/c) supernovae in the central 1 kpc region of spiral galaxies are at least as high as, and perhaps higher than, those in the outer regions. This is the first direct evidence that stellar bulges in spiral galaxies are not efficient SNe Ⅰa producers and that novae and nova-like systems in the bulges are therefore not efficient producers of SNe Ⅰa. The radial distribution of all types of supernovae are, within errors, the same beyond ～7 kpc. So SNe Ⅰa are also unlikely to come from a halo population. We also analyze a subsample of SNe Ⅰa including the Calan/Tololo sample and 11 nearby well-observed SNe Ⅰa for which accurate photometry is available. Supernovae at more than 7.5 kpc from the galactic center show 3-4 times smaller scatter in brightness than those closer to the center. This behavior represents an important new constraint on evolutionary models of SNe Ⅰa and their correlation with the underlying stellar population. SNe Ⅰa at larger galactocentric distances may define a more homogeneous group for measuring cosmological distances. The B_(max), V_(max), and I_(max) magnitudes for SNe Ⅰa beyond 7.5 kpc from the center of the host galaxies were found to be -19.05 ± 0.20, -19.07 ± 0.18, and -18.81 ± 0.18, respectively.