A limit on the number density of bright z ≈ 7 galaxies

We present a survey of bright optical dropout sources in two deep, multiwavelength surveys comprising 11 widely separated fields, aimed at constraining the galaxy luminosity function at z approximate to 7 for sources at 5-10 L* (z = 6). Our combined survey area is 225 arcmin(2) to a depth of J(AB) = 24.2 (3 sigma) and 135 arcmin(2) to J = 25.3 (4 sigma). We find that infrared data longwards of 2 mu m are essential for classifying optical dropout sources, and in particular for identifying cool Galactic star contaminants. Our limits on the number density of high-redshift sources are consistent with current estimates of the Lyman break galaxy luminosity function at z = 6.