We report on our analysis of the VISTA Orion ZYJHK _ { s } photometric data ( completeness magnitudes of Z = 22.6 and J = 21.0 mag ) focusing on a circular area of 2798.4 arcmin ^ { 2 } around the young \sigma  Orionis star cluster ( \sim 3 Myr , \sim 352 pc , and solar metallicity ) .
The combination of the VISTA photometry with optical , WISE and Spitzer data allows us to identify a total of 210 \sigma  Orionis member candidates with masses in the interval 0.25–0.004 M _ { \odot } , 23 of which are new planetary-mass object findings .
These discoveries double the number of cluster planetary-mass candidates known so far .
One object has colors compatible with a T spectral type .
The \sigma  Orionis cluster harbors about as many brown dwarfs ( 69 , 0.072–0.012 M _ { \odot } ) and planetary-mass objects ( 37 , 0.012–0.004 M _ { \odot } ) as very low-mass stars ( 104 , 0.25–0.072 M _ { \odot } ) .
Based on Spitzer data , we derive a disk frequency of \sim 40 %  for very low-mass stars , brown dwarfs , and planetary mass objects in \sigma  Orionis .
The radial density distributions of these three mass intervals are alike : all are spatially concentrated within an effective radius of 12′Â ( 1.2 pc ) around the multiple star \sigma Ori , and no obvious segregation between disk-bearing and diskless objects is observed .
Using the VISTA data and the Mayrit catalog , we derive the cluster mass spectrum ( \Delta N / \Delta M \sim M ^ { - \alpha } ) from \sim 19 to 0.006 M _ { \odot } ( VISTA ZJ completeness ) , which is reasonably described by two power-law expressions with indices of \alpha = 1.7 \pm 0.2 for M > 0.35 M _ { \odot } , and \alpha = 0.6 \pm 0.2 for M < 0.35 M _ { \odot } .
The \sigma  Orionis mass spectrum smoothly extends into the planetary-mass regime down to 0.004 M _ { \odot } .
Our findings of T-type sources ( < 0.004 M _ { \odot } ) in the VISTA \sigma  Orionis exploration appear to be smaller than what is predicted by the extrapolation of the cluster mass spectrum down to the survey J -band completeness .