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

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

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 Jupiter masses (MJ). 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 2-10 MJ. Programs to date have not been sensitive enough to probe the hypothesized opacity limit of fragmentation. Here we present the first identification of a turnover in the initial mass function below 12 MJ 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 ~ 3 MJ with sensitivity to 0.5 MJ. We present evidence for a double power law model increasing from about 60 MJ to roughly 12 MJ, consistent with previous studies, followed by a decrease down to 0.5 MJ. 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 MJ.
http://arxiv.org/abs/2409.04624

The JWST/NIRISS Deep Spectroscopic Survey for Young Brown Dwarfs and Free-Floating Planets

The discovery and characterization of free-floating planetary-mass objects (FFPMOs) is fundamental to our understanding of star and planet formation. Here we report results from an extremely deep spectroscopic survey of the young star cluster NGC1333 using NIRISS WFSS on the James Webb Space Telescope. The survey is photometrically complete to K~21, and includes useful spectra for objects as faint as K~20.5. The observations cover 19 known brown dwarfs, for most of which we confirm spectral types using NIRISS spectra. We discover six new candidates with L-dwarf spectral types that are plausible planetary-mass members of NGC1333, with estimated masses between 5-15 MJup. One, at ~5 MJup, shows clear infrared excess emission and is a good candidate to be the lowest mass object known to have a disk. We do not find any objects later than mid-L spectral type (M less than 4 MJup). The paucity of Jupiter-mass objects, despite the surveys unprecedented sensitivity, suggests that our observations reach the lowest mass objects formed like stars in NGC1333. Our findings put the fraction of FFPMOs in NGC1333 at ~10% of the number of cluster members, significantly more than expected from the typical log-normal stellar mass function. We also search for wide binaries in our images and report a young brown dwarf with a planetary-mass companion.
http://arxiv.org/abs/2408.12639