Identification of a turnover in the initial mass function of a young stellar cluster down to 0.5 M${}_J$

Abstract

A successful theory of star formation should predict the number of objects as a function of their mass produced through star-forming events. Previous studies in star-forming regions and the solar neighborhood identify a mass function increasing from the hydrogen-burning limit down to about 10 M${}_J$. Theory predicts a limit to the fragmentation process, providing a natural turnover in the mass function down to the opacity limit of turbulent fragmentation thought to be near 1-10 M${}_J$. Programs to date have not been sensitive enough to probe the hypothesized opacity limit of fragmentation. We present the first identification of a turnover in the initial mass function below 12 M${}_J$ within NGC 2024, a young star-forming region. With JWST/NIRCam deep exposures across 0.7-5 $\mu$m, we identified several free floating objects down to roughly 3 M${}_J$ with sensitivity to 0.5 M${}_J$. We present evidence for a double power law model increasing from about 60 M${}_J$ to roughly 12 M${}_J$, consistent with previous studies, followed by a decrease down to 0.5 M${}_J$. Our results support the predictions of star and brown dwarf formation theory, identifying the theoretical turnover in the mass function and suggest the fundamental limit of turbulent fragmentation near 3 M${}_J$.

10 pages, 5 figures, accepted to ApJL Feb 21 2025

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