Using Hubble Space Telescope ( HST ) photometry to measure star formation histories , we age-date the stellar populations surrounding supernova remnants ( SNRs ) in M31 and M33 .
We then apply stellar evolution models to the ages to infer the corresponding masses for their supernova progenitor stars .
We analyze 33 M33 SNR progenitors and 29 M31 SNR progenitors in this work .
We then combine these measurements with 53 previously published M31 SNR progenitor measurements to bring our total number of progenitor mass estimates to 115 .
To quantify the mass distributions , we fit power laws of the form dN / dM \propto M ^ { - \alpha } .
Our new larger sample of M31 progenitors follows a distribution with \alpha = 4.4 ^ { +0.4 } _ { -0.4 } , and the M33 sample follows a distribution with \alpha = 3.8 ^ { +0.4 } _ { -0.5 } .
Thus both samples are consistent within the uncertainties , and the full sample across both galaxies gives \alpha = 4.2 ^ { +0.3 } _ { -0.3 } .
Both the individual and full distributions display a paucity of massive stars when compared to a Salpeter initial mass function ( IMF ) , which we would expect to observe if all massive stars exploded as SN that leave behind observable SNR .
If we instead fix \alpha = 2.35 and treat the maximum mass as a free parameter , we find M _ { max } { \sim } 35 - 45 M _ { \odot } , indicative of a potential maximum cutoff mass for SN production .
Our results suggest that either SNR surveys are biased against finding objects in the youngest ( < 10 Myr old ) regions , or the highest mass stars do not produce SNe .