A JWST Survey for Free-flaoting Brown Dwarfs Down to the Mass of Jupiter

We present the results of a JWST survey for free-floating brown dwarfs down to the mass of Jupiter in the nearby star-forming cluster IC 348. Through this work, we have spectroscopically confirmed 11 new brown dwarfs within the cluster. The faintest new objects have mass estimates of 2 Jupiter masses, making them the least massive known brown dwarfs and providing a new constraint on the minimum mass of the IMF. There remain 19 additional promising candidates that lack spectroscopy. Ten of the confirmed brown dwarfs and one previously known member exhibit absorption in the 3.4um fundamental band of an unidentified aliphatic hydrocarbon, which was not predicted by atmospheric models and was not previously detected in atmospheres outside of the solar system. Among the brown dwarfs in IC 348 that have hydrocarbon detections, the features are stronger at fainter magnitudes, indicating that the hydrocarbon is a natural constituent of the atmospheres of the coolest newborn brown dwarfs. We propose a new spectral class "H" that is defined by the presence of the 3.4um band of the hydrocarbon. One of the new brown dwarfs at 2 Jupiter masses exhibits large excess emission from a circumstellar disk, making it the least massive known brown dwarf with a disk.