We measure new estimates for the galaxy stellar mass function and star formation rates for samples of galaxies at z \sim 4 ,~ { } 5 ,~ { } 6 ~ { } \&~ { } 7 using data in the CANDELS GOODS South field .
The deep near-infrared observations allow us to construct the stellar mass function at z \geq 6 directly for the first time .
We estimate stellar masses for our sample by fitting the observed spectral energy distributions with synthetic stellar populations , including nebular line and continuum emission .
The observed UV luminosity functions for the samples are consistent with previous observations , however we find that the observed M _ { UV } - M _ { * } relation has a shallow slope more consistent with a constant mass to light ratio and a normalisation which evolves with redshift .
Our stellar mass functions have steep low-mass slopes ( \alpha \approx - 1.9 ) , steeper than previously observed at these redshifts and closer to that of the UV luminosity function .
Integrating our new mass functions , we find the observed stellar mass density evolves from \log _ { 10 } \rho _ { * } = 6.64 ^ { +0.58 } _ { -0.89 } at z \sim 7 to 7.36 \pm 0.06 \text { M } _ { \odot } \text { Mpc } ^ { -3 } at z \sim 4 .
Finally , combining the measured UV continuum slopes ( \beta ) with their rest-frame UV luminosities , we calculate dust corrected star-formation rates ( SFR ) for our sample .
We find the specific star-formation rate for a fixed stellar mass increases with redshift whilst the global SFR density falls rapidly over this period .
Our new SFR density estimates are higher than previously observed at this redshift .