We present the results of a H - and K - band multi-object and long-slit spectroscopic survey of substellar mass candidates in the outer regions of the Orion Nebula Cluster .
The spectra were obtained using MOIRCS on the 8.2-m Subaru telescope and ISLE on the 1.88-m telescope of Okayama Astronomical Observatory .
Eight out of twelve spectra show strong water absorptions and we confirm that their effective temperatures are \leq 3000 K ( spectral type \geq M6 ) from a chi-square fit to synthetic spectra .
We plot our sources on an HR diagram overlaid with theoretical isochrones of low-mass objects and identify three new young brown dwarf candidates .
One of the three new candidates is a cool object near the brown dwarf and planetary mass boundary .
Based on our observations and those of previous studies , we determine the stellar ( 0.08 < M / M _ { \odot } < 1 ) to substellar ( 0.03 < M / M _ { \odot } < 0.08 ) mass number ratio in the outer regions of the Orion nebular cluster to be 3.5 \pm 0.8 .
In combination with the number ratio reported for the central region ( 3.3 ^ { +0.8 } _ { -0.7 } ) , this result suggests the number ratio does not simply change with the distance from the center of the Orion nebular cluster .