Number Density of Bright Lyman-Break Galaxies at z ∼ 6 in the Subaru Deep Field

Abstract

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