The deep , wide-area ( \sim 800-900 arcmin ^ { 2 } ) near-infrared/WFC3/IR + Spitzer /IRAC observations over the CANDELS fields have been a remarkable resource for constraining the bright end of high redshift UV luminosity functions ( LFs ) .
However , the lack of HST 1.05 \mu m observations over the CANDELS fields has made it difficult to identify z \sim 9 -10 sources robustly , since such data are needed to confirm the presence of an abrupt Lyman break at 1.2 \mu m. We report here on the successful identification of many such z \sim 9-10 sources from a new HST program ( z9-CANDELS ) that targets the highest-probability z \sim 9-10 galaxy candidates with observations at 1.05 \mu m , to search for a robust Lyman-break at 1.2 \mu m. The potential z \sim 9-10 candidates are preselected from the full HST , Spitzer /IRAC S-CANDELS observations , and the deepest-available ground-based optical+near-infrared observations ( CFHTLS-DEEP+HUGS+UltraVISTA+ZFOURGE ) .
We identified 15 credible z \sim 9-10 galaxies over the CANDELS fields .
Nine of these galaxies lie at z \sim 9 and 5 are new identifications .
Our targeted follow-up strategy has proven to be very efficient in making use of scarce HST time to secure a reliable sample of z \sim 9 -10 galaxies .
Through extensive simulations , we replicate the selection process for our sample ( both the preselection and follow-up ) and use it to improve current estimates for the volume density of bright z \sim 9 and z \sim 10 galaxies .
The volume densities we find are 5 _ { -2 } ^ { +3 } \times and 8 _ { -3 } ^ { +9 } \times lower , respectively , than found at z \sim 8 .
When compared with the best-fit evolution ( i.e. , d \log _ { 10 } \rho _ { UV } / dz = -0.29 \pm 0.02 ) in the UV luminosities densities from z \sim 8 to z \sim 4 integrated to 0.3 L _ { z = 3 } ^ { * } ( -20 mag ) , these luminosity densities are 2.6 _ { -0.9 } ^ { +1.5 } \times and 2.2 _ { -1.1 } ^ { +2.0 } \times lower , respectively , than the extrapolated trends .
Our new results are broadly consistent with the “ accelerated evolution ” scenario at z > 8 , as seen in many theoretical models .