The IMF of Field OB Stars in the Small Magellanic Cloud

TL;DR

This study uses spectroscopic data from the RIOTS4 survey to analyze the initial mass function of field OB stars in the Small Magellanic Cloud, revealing a steeper slope than the canonical IMF.

Contribution

It provides the first empirical measurement of the field stellar IMF in the SMC, highlighting a significantly steeper slope and no upper mass limit up to 65 solar masses.

Findings

Field IMF slope is Gamma = 2.9, much steeper than the canonical 1.35.

No evidence of an upper mass limit up to 65 solar masses.

The survey offers a comprehensive dataset for studying massive stars in the SMC.

Abstract

The population of field OB stars are an important component of a galaxy's stellar content, representing 20-30% of the massive stars. To study this population, we have undertaken the Runaways and Isolated O Type Star Spectroscopic Survey of the SMC (RIOTS4). RIOTS4 surveys a spatially complete sample of >350 field OB stars in the Small Magellanic Cloud and will serve as a key probe of runaways, binaries, and the stellar IMF in the field massive star population. Here, we focus on the field IMF, which provides an empirical probe of the star-forming process and is a fundamental property of a stellar population. Together with photometry from the OGLE survey, RIOTS4 will yield a definitive stellar IMF for the SMC field massive star population. We present preliminary results that suggests the field IMF is much steeper, Gamma = 2.9, than the canonical stellar IMF of Gamma = 1.35. Despite the steep slope, we see no evidence of a stellar upper mass limit, up to our highest mass star of 65 solar masses.