2012AJ....143...79Y

We present the results of the extensive narrowband survey of Lyα emission-line objects at z = 3.1 in the 1.38 deg² area surrounding the high-density region of star-forming galaxies at z = 3.09 in the SSA22 field, as well as in the 1.04 deg² area of the three separated general blank fields. In total, of 2161 Lyα emitters, there are 1394 in the SSA22 fields and 767 in the general fields detected at the narrowband AB magnitude limit of 25.73, which corresponds to the line flux of ~1.8x10^–17 erg/s/cm2 or the luminosity of ~1.5x10⁴² erg/s at z = 3.1, above the observed equivalent-width threshold, ~190 Å. The average surface number density of the emitters at z = 3.1 in the general fields above the thresholds is 0.20±0.01/arcmin2. The SSA22 high-density region at z = 3.09, whose peak local density is six times that of the average, is found to be the most prominent outstanding structure in the whole surveyed area and is firmly identified as a robust "protocluster." We also compared the overdensity of the 100 arcmin² and 700 arcmin² areas which contain the protocluster with the expected fluctuation of the dark matter as well as those of the model galaxies in cosmological simulations. We found that the peak height values of the overdensity are 8-10 and 3-4 times the expected standard deviations for the counts of Lyα emitters at z = 3.1 in the corresponding volume, respectively. We conclude that the structure at z = 3.09 in the SSA22 field is a very significant and rare density peak up to the scale of ~60 Mpc.