Infrared spectroscopy of free-floating planet candidates in Upper Scorpius and Ophiuchus

Context. A rich population of low-mass brown dwarfs and isolated planetary mass objects has been reported in the Upper Scorpius and Ophiuchus star-forming complex.
Aims: We investigate the membership, nature, and properties of 17 of these isolated planetary mass candidates using low-resolution near-infrared spectra.
Methods: We investigated the membership by looking for evidence of their youth using four diagnostics: the slope of the continuum between the J and Ks band, the H_cont, and the TLI-g gravity-sensitive indices. In addition, we compared the spectra to young and field (old) M and L-dwarf standards.
Results: All the targets but one are confirmed as young ultracool objects, with spectral types between L0 and L6 and masses in the range 0.004-0.013 M_⊙, according to evolutionary models. The status of the last target is unclear at this point.
Conclusions: Only one possible contaminant has been identified among the 17 targets, suggesting that the contamination level of the original sample must be low (≲6%).

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