We present the discovery of four surprisingly bright ( H _ { 160 } \sim 26 - 27 mag AB ) galaxy candidates at z \sim 9 - 10 in the complete HST CANDELS WFC3/IR GOODS-N imaging data , doubling the number of z \sim 10 galaxy candidates that are known , just \sim 500 Myr after the Big Bang .
Two similarly bright sources are also detected in a systematic re-analysis of the GOODS-S data set .
Three of the four galaxies in GOODS-N are significantly detected at 4.5 - 6.2 \sigma in the very deep Spitzer /IRAC 4.5 \mu m data , as is one of the GOODS-S candidates .
Furthermore , the brightest of our candidates ( at z = 10.2 \pm 0.4 ) is robustly detected also at 3.6 \mu m ( 6.9 \sigma ) , revealing a flat UV spectral energy distribution with a slope \beta = -2.0 \pm 0.2 , consistent with demonstrated trends with luminosity at high redshift .
The abundance of such luminous candidates suggests that the luminosity function evolves more significantly in \phi _ { * } than in L _ { * } at z \gtrsim 8 with a higher number density of bright sources than previously expected .
Despite the discovery of these luminous candidates , the cosmic star formation rate density for galaxies with SFR > 0.7 M _ { \odot } yr ^ { -1 } shows an order-of-magnitude increase in only 170 Myr from z \sim 10 to z \sim 8 , consistent with previous results given the dominance of low-luminosity sources to the total SFR density .
Based on the IRAC detections , we derive galaxy stellar masses at z \sim 10 , finding that these luminous objects are typically 10 ^ { 9 } M _ { \odot } .
This allows for a first estimate of the cosmic stellar mass density at z \sim 10 resulting in \log _ { 10 } \rho _ { * } = 4.7 ^ { +0.5 } _ { -0.8 } M _ { \odot } Mpc ^ { -3 } for galaxies brighter than M _ { UV } \sim - 18 .
The remarkable brightness , and hence luminosity , of these z \sim 9 - 10 candidates highlights the opportunity for deep spectroscopy to determine their redshift and nature , demonstrates the value of additional search fields covering a wider area to understand star-formation in the very early universe , and highlights the opportunities for JWST to map the buildup of galaxies at redshifts much earlier than z \sim 10 .