English: This image shows a brown dwarf - planetary-mass object binary in the star cluster NGC 1333 discovered with JWST/NIRISS.

Original text:

The JWST/NIRISS Deep Spectroscopic Survey for Young Brown Dwarfs and Free-Floating Planets (Adam B. Langeveld et al. arxiv pre-print https://doi.org/10.48550/arXiv.2408.12639 accepted for AJ)

Abstract:

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 < ~4 MJup). The paucity of Jupiter-mass objects, despite the survey's 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.

Figure 15.

Results of the spectroscopic survey for object NIRISS-NGC1333-10B (NN10B) – the companion object of the binary NN10 (with NN10A shown in Figure 14). Panels shown are the same as Figure 5. Similarly to NN10A (Figure 14), there is contamination in the F200W spectrum from a source that overlaps with the spectral trail – the data in this region is unusable and was removed (evident by the gap in the spectrum in the top panel between ∼ 1.95–2.1 μm). The cutouts also display a large white region (where all values are NaNs) to remove the spectrum of the primary object.