Early Growth of the Star Formation Rate Function in the Epoch of Reionization: an Approach with Rest-frame Optical Emissions

Abstract

We present a star formation rate function (SFRF) at $z\sim 6$ based on star formation rates (SFRs) derived by spectral energy distribution (SED) fitting on data from rest-frame UV to optical wavelength of galaxies in the CANDELS GOODS-South and North fields. The resulting SFRF shows an excess compared to the previous estimations by using rest-frame UV luminosity functions (LFs) corrected for the dust attenuation, and is comparable to that estimated from a far-infrared LF. This suggests that the number density of dust-obscured intensively star-forming galaxies at $z\sim 6$ has been underestimated in the previous approach based only on rest-frame UV observations. We parameterize the SFRF with using the Schechter function and obtain the best-fit parameter of the characteristic SFR (${\mathrm{SFR}}^{\ast }$) when the faint-end slope and characteristic number density are fixed. The best-fit ${\mathrm{SFR}}^{\ast }$ at $z\sim 6$ is comparable to that at $z\sim 2$, when the cosmic star formation activity reaches its peak. Together with SFRF estimations with similar approach using rest-frame UV to optical data, the ${\mathrm{SFR}}^{\ast }$ is roughly constant from $z\sim 2$ to $z\sim 6$ and may decrease above $z\sim 6$. Since the ${\mathrm{SFR}}^{\ast }$ is sensitive to the high-SFR end of the SFRF, this evolution of ${\mathrm{SFR}}^{\ast }$ suggests that the high-SFR end of the SFRF grows rapidly during the epoch of reionization and reaches a similar level observed at $z\sim 2$.

24 pages, 14 figures, and 3 tables. Accepted for publication in ApJ