Number density of bright Lyman-break galaxies at z similar to 6 in the Subaru Deep Field

We report on bright Lyman-break galaxies (LBGs) selected in a 767 arcmin(2) area of the Subaru Deep Field. The selection was made in the i - z(R) versus z(B) - z(R) plane, where z(B) and z(R) are new bandpasses with a central wavelength of 8842 angstrom and 9841 angstrom, respectively. We detected 12 LBG candidates down to z(R) = 25.4, and calculated the normalization of the rest-frame far-ultraviolet (FUV: similar or equal to 1400 angstrom) luminosity function at M-FUV = -21.6 to be phi(-21.6) = (2.6 +/- 0.7) x 10(-5) mag(-1) Mpc(-3). This must be the most reliable measurement ever obtained of the number density of bright z similar to 6 LBGs, because it is more robust against both contamination and cosmic variance than previous values. The FUV luminosity density contributed from LBGs brighter than MFUV = -21.3 is (2.8 +/- 0.8) x 10(24) erg s(-1) Hz(-1) Mpc(-3), which is equivalent to a star-formation rate density of (3.5 +/- 1.0) x 10(-4) M-circle dot yr(-1) Mpc(-3). We find that the FUV luminosity density of bright galaxies increases by an order of magnitude from z similar to 6 to similar to 3, and then drops by 10(3) from z similar to 3 to the present epoch. The evolutionary behavior of bright LBGs resembles that of luminous dusty star-forming galaxies and bright QSOs. The redshift of z similar to 3 appears to be a remarkable era in the cosmic history when massive galaxies were being intensively formed.