Using the bright galaxy counts from the 2 Micron All Sky Survey ( 2MASS ) second incremental release , two techniques for probing large-scale structure at distances of \sim~ { } 150 h ^ { -1 } Mpc are investigated .
First , we study the counts from two sets of six 5 ^ { \circ } \times \sim~ { } 80 ^ { \circ } strips in the two galactic caps .
In the six southern strips a deficit of \sim 30 per cent was found relative to a predicted homogeneous distribution at K _ { s } \sim 11 .
These strips were also in good agreement with a model incorporating the radial density function of the southern 2dF Galaxy Redshift Survey ( 2dFGRS ) , which shows a deep underdensity between \sim 90 and 180 h ^ { -1 } Mpc .
Together with a similar underdensity found in the Las Campanas Redshift Survey , these results indicate a very large ‘ local hole ’ in the Southern Galactic Cap ( SGC ) to \sim > 150 h ^ { -1 } Mpc with a linear size across the sky of \sim 200 h ^ { -1 } Mpc but with a significantly lower mean underdensity of \sim 30 per cent than that suggested by the bright APM SGC counts .
The counts in the northern set of strips are low overall but indicate a more varied pattern .
When all the available 2MASS data with |b| > 30 ^ { \circ } were aggregated , they indicated underdensities of \sim 18 per cent and \sim 30 per cent at K _ { s } \sim 11 for the northern and southern areas respectively .
Our second method uses the ratio of the counts with 11.38 < K _ { s } < 12.38 to 12.88 < K _ { s } < 13.38 binned in 25 deg ^ { 2 } areas ; the counts from these areas provide a smoothed map over the sky of the slope in the counts between K _ { s } =11.38 and 13.38 .
Visually , the resulting map shows the expected complex form of the cosmic web and picks out known rich clusters , demonstrating the usefulness of this ‘ slope statistic ’ as a probe of large-scale structure at distances of \sim < 150 h ^ { -1 } Mpc .
Most interestingly , the map also shows large regions , \sim 100 ^ { \circ } across , of steep counts in both hemispheres .
Thus , the present 2MASS data suggest the presence of a potentially huge contiguous void stretching from south to north .
Not only would this delineate further the limits for the Cosmological Principle but it would also show the possible presence of significant power on scales of \sim > 300 h ^ { -1 } Mpc in the galaxy power spectrum .