The host galaxies of Type Ia supernovae at z= 0.6

Abstract

We examine the host galaxies of high-redshift Type Ia supernovae (SNe Ia) using archival I- and R-band data from the Hubble Space Telescope. The SNe Ia host galaxies show a wide variety of morphologies, including undisturbed ellipticals, spirals and disturbed systems. SNe Ia are also found over a wide range of projected distances from the host galaxy centres, ranging from 3 kpc to ~30 kpc. For a sample of 22 SNe Ia at <z>= 0.6, ~70 per cent are found in spiral galaxies and ~30 per cent are found in elliptical systems, similar to the proportions observed locally. Including data from Ellis & Sullivan (2001), we find no significant difference in the average light-curve shape-corrected M_B^peak for high-z SNe Ia between spirals and ellipticals. These results are consistent with predictions based on the locally derived understanding of SNe Ia physics and the influence of progenitor mass and metallicity. We also construct colour maps for two host galaxies and find that both show a non-uniform colour structure with typical variations of rest-frame B-V~ 0.5. This is most plausibly attributed to the presence of, and variation in, dust extinction in these galaxies. Moreover, we find no evidence that the SNe Ia are preferentially found in outer regions (> 10 kpc) of the host galaxies where extinction would be low. This suggests that the range of host galaxy extinctions of SNe Ia at z~ 0.6 should be comparable to those of local SNe Ia. Although observational bias cannot be completely ruled out, this appears to be in conflict with the finding of low extinction for SNe Ia found in the high-z supernova search studies.