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

TL;DR

This study uses JWST data to identify a turnover in the initial mass function of a young stellar cluster below 12 Jupiter masses, supporting theories of star formation and turbulent fragmentation limits.

Contribution

First observational evidence of a turnover in the initial mass function below 12 M$_{J}$, down to 0.5 M$_{J}$, confirming theoretical predictions about fragmentation limits.

Findings

Detected objects down to 3 M$_{J}$ with JWST/NIRCam.

Identified a decrease in the mass function below 12 M$_{J}$.

Supported the theoretical limit of turbulent fragmentation near 3 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$_{J}$.