Some theories of star formation suggest massive stars may only form in clustered environments , which would create a deficit of massive stars in low density environments .
Observationally , Massey ( 2002 ) finds such a deficit in samples of the field population in the Small and Large Magellanic Clouds , with an IMF slope of \Gamma _ { IMF } \sim 4 .
These IMF measurements represent some of the largest known deviations from the standard Salpeter IMF slope of \Gamma _ { IMF } = 1.35 .
Here , we carry out a comprehensive investigation of the mass function above 20 M _ { \odot } for the entire field population of the Small Magellanic Cloud , based on data from the Runaways and Isolated O Type Star Spectroscopic Survey of the SMC ( RIOTS4 ) .
This is a spatially complete census of the entire field OB star population of the SMC obtained with the IMACS multi-object spectrograph and MIKE echelle spectrograph on the Magellan telescopes .
Based on Monte-Carlo simulations of the evolved present-day mass function , we find the slope of the field IMF above 20 M _ { \odot } is \Gamma _ { IMF } =2.3 \pm 0.4 .
We extend our IMF measurement to lower masses using BV photometry from the OGLE II survey .
We use a statistical approach to generate a probability distribution for the mass of each star from the OGLE photometry , and we again find \Gamma _ { IMF } =2.3 \pm 0.6 for stellar masses from 7 M _ { \odot } to 20 M _ { \odot } .
The discovery and removal of ten runaways in our RIOTS4 sample steepens the field IMF slope to \Gamma _ { IMF } =2.8 \pm 0.5 .
We discuss the possible effects of binarity and star-formation history on our results , and conclude that the steep field massive star IMF is most likely a real effect .