We present an Ultra-Cool Dwarf ( UCD ) catalogue compiled from low southern Galactic latitudes and mid-plane , from a cross-correlation of the 2MASS and SuperCOSMOS surveys .
The catalogue contains 246 members identified from 5042 deg ^ { 2 } within 220 ^ { \circ } \leqslant \ell \leqslant 360 ^ { \circ } and 0 ^ { \circ } < \ell \leqslant 30 ^ { \circ } , for | \mbox { { \em b } } | \leqslant 15 ^ { \circ } .
Sixteen candidates are spectroscopically confirmed in the near-IR as UCDs with spectral types from M7.5V to L9 , the latest being the unusual blue L dwarf 2MASS J11263991-5003550 .
Our catalogue selection method is presented enabling UCDs from \sim M8V to the L–T transition to be selected down to a 2MASS limiting magnitude of \mbox { { \em K } $ { } _ { s } $ } \simeq 14.5 \mbox { mag } ( for \mbox { SNR } \geqslant 10 ) .
This method does not require candidates to have optical detections for catalogue inclusion .
An optimal set of optical/near-IR and reduced proper-motion selection criteria have been defined that includes : an R _ { F } and I _ { N } photometric surface gravity test , a dual R _ { F } -band variability check , and an additional photometric classification scheme to selectively limit numbers of potential contaminants in regions of severe overcrowding .
We identify four candidates as possible companions to nearby Hipparcos stars – observations are needed to identify these as potential benchmark UCD companions .
We also identify twelve UCDs within a possible distance 20 pc , three are previously unknown of which two are estimated within 10 pc , complimenting the nearby volume-limited census of UCDs .
An analysis of the catalogue spatial completeness provides estimates for distance completeness over three UCD M _ { J } ranges , while Monte-Carlo simulations provide an estimate of catalogue areal completeness at the 75 per cent level .
We estimate a UCD space density of \rho _ { ( total ) } = ( 6.41 \pm 3.01 ) \times 10 ^ { -3 } { pc } ^ { -3 } over the range of 10.5 \leqslant \mbox { { \em M } $ { } _ { J } $ } \la 14.9 , similar to values measured at higher Galactic latitudes ( | \mbox { { \em b } } | \ga 10 ^ { \circ } ) in the field population and obtained from more robust spectroscopically confirmed UCD samples .