Identification of a turnover in the initial mass function of a young stellar cluster down to 0.5 MJ

Abstract We present results exploring the initial mass function in a young (< 1 Myr) embedded star-forming region, NGC 2024, down to sub-Jupiter masses using the Near Infrared Camera (NIRCam) on the James Webb Space Telescope (JWST). Predominant star formation theory predicts a mass limit for the formation of objects produced through the fragmentation of molecular clouds, 2-10 MJ. Previous studies identified an increasing mass function from the hydrogen-burning limit down to ~ 10 MJ, but were not sensitive to lower mass objects. In GTO-1190 (PI: M.R. Meyer), we obtained deep imaging of the central core of NGC 2024, covering 0.7 - 5 μm and sensitive down to 0.5 MJ, and extracted photometry for 48 candidate members of the cluster. We find that a broken power-law model of the mass function best represents the data, increasing from 60 MJ to 12 MJ then followed by a decrease down to 0.5 MJ. This is the first evidence for a decrease in the mass function below 10 MJ in a stellar population. Our program probes the lowest masses theoretically produced through star formation processes, finding no likely cluster members below about 3 MJ, potentially the fundamental limit of the star and brown dwarf formation process.