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

Abstract

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 ~ 7 for sources at 5-10L*(z = 6). Our combined survey area is 225arcmin² to a depth of J_AB = 24.2 (3σ) and 135arcmin² to J = 25.3 (4σ). We find that infrared data longwards of 2μm 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.