Large-Scale Structure of Emission-Line Galaxies at z = 3.1*

We obtained a deep wide-field (32' ? 24') narrowband (?c = 4977?,?? = 77?) image of a field including the protocluster at z = 3.1 in the SSA22a field studied by Steidel et al. using the Subaru Telescope. The field we observed is about 10 times as large as that studied by Steidel et al. We detected 283 highly confident strong Ly? emitter candidates at z ~ 3.1 down to 25.8 AB mag with the observed equivalent width larger than 154 ?. These strong Ly? emitter candidates show a highly nonuniform distribution with the beltlike region of high surface density, which is found to extend over ~60 Mpc in comoving scale. The average number density of the strong Ly? emitter candidates in this high-density region is 3 times as high as that of a blank field. The probability of finding such a large-scale high-density peak is as small as 0.1% in the context of the CDM structure formation scenario, if we assume a linear bias parameter b ~ 4. In addition to these strong Ly? emitters, we also detected 49 Ly? absorbers, which show significant deficit in the narrowband image. We further detected 74 extended emitters, which have significant fluxes over the areas of 18 arcsec2 or more. Interestingly, both these absorbers and extended emitters show sky distributions very similar to that of the strong Ly? emitters. This supports the reality of the large-scale structure at z = 3.1 and suggests that galaxy formation preferentially occurs in the high-density region of strong Ly? emitters.