P. Garnavich: What do host galaxies of Ia supernovae tell us
It's important to understand host galaxy properties of Ia SNe to beat down the systematic uncertainties in the SN photometry => better determination of cosmological parameters.
Ia SNe ar not good standard candles (vary by a factor of 10-30). Dust extinction laws has to be used to correct or dust in hosts. This uses the obserevd colours of the SNe. Measure the host galaxy properties to constrain this and other uncertainties: (i) Metallicity; (ii) Star formation history; (iii) Dust properties.
A strong division of Ia properties in different host morpholgies is known and confirmed with the current sample. Fast declining Ia's preferntially in spiral/SF galaxies (need more than morphology, spectra better than colours). Perhaps due to a brightness-metallicity relation? No clear trend found for decline rate vs host metallicity. Fast SNe found only(!) in hosts with very low SFR (more important than the metallicity). A correlation of SFR in galaxies and numbers of bright SNe how that brighter SNe are more common in galaxies with higher SFR. No clear change with redshift of this is detected (SNLS result).
There are many more high SFR galaxies in the field than as SN hosts, P.G. claim this is support for delay times of Ia's (or rather a second delay time "channel", having Ia SNe that are not related to the ongoing SF in the galaxies).