Using Hubble Space Telescope ( HST ) photometry , we age-date 59 supernova remnants ( SNRs ) in the spiral galaxy M31 and use these ages to estimate zero-age main sequence masses ( M _ { ZAMS } ) for their progenitors .
To accomplish this , we create color-magnitude diagrams ( CMDs ) and employ CMD fitting to measure the recent star formation history ( SFH ) of the regions surrounding cataloged SNR sites .
We identify any young coeval population that likely produced the progenitor star , then assign an age and uncertainty to that population .
Application of stellar evolution models allows us to infer the M _ { ZAMS } from this age .
Because our technique is not contingent on identification or precise location of the progenitor star , it can be applied to the location of any known SNR .
We identify significant young star formation around 53 of the 59 SNRs and assign progenitor masses to these , representing a factor of \sim 2 increase over currently measured progenitor masses .
We consider the remaining 6 SNRs as either probable Type Ia candidates or the result of core-collapse progenitors that have escaped their birth sites .
In general , the distribution of recovered progenitor masses is bottom heavy , showing a paucity of the most massive stars .
If we assume a single power law distribution , dN / dM \propto M ^ { \alpha } , we find a distribution that is steeper than a Salpeter IMF ( \alpha = -2.35 ) .
In particular , we find values of \alpha outside the range -2.7 \geq \alpha \geq - 4.4 to be inconsistent with our measured distribution at 95 % confidence .
If instead we assume a distribution that follows a Salpeter IMF up to some maximum mass , we find that values of M _ { Max } > 26 are inconsistent with the measured distribution at 95 % confidence .
In either scenario , the data suggest that some fraction of massive stars may not explode .
The result is preliminary and requires more SNRs and further analysis .
In addition , we use our distribution to estimate a minimum mass for core collapse between 7.0 and 7.8 M _ { \odot } .