THE BRIGHT END OF THE z ∼ 9 AND z ∼ 10 UV LUMINOSITY FUNCTIONS USING ALL FIVE CANDELS FIELDS

The deep, wide-area (similar to 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. However, the lack of Hubble Space Telescope (HST) 1.05 mu m observations over the CANDELS fields has made it difficult to identify z similar to 9-10 sources robustly, since such data are needed to confirm the presence of an abrupt Lyman break at 1.2 mu m. Here, we report on the successful identification of many such z similar to 9-10 sources from a new HST program (z9-CANDELS) that targets the highest-probability z similar to 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 similar to 9-10 candidates were 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 similar to 9-10 galaxies over the CANDELS fields. Nine of these galaxies lie at z similar to 9 and five 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 similar to 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 similar to 9 and z similar to 10 galaxies. The volume densities we find are 5(-2)(+3)x and 8(-3)(+9)x lower, respectively, than those found at z similar to 8. When compared with the best-fit evolution (i.e., d log(10) rho(UV)/dz = -0.29 +/- 0.02) in the UV luminosity densities from z similar to 8 to z similar to 4 integrated to 0.3L(z=3)* (-20 mag), these luminosity densities are 2.6(-0.9)(+1.5)x and 2.2(-1.1)(+2.0) lower, respectively, than the extrapolated trends. Our new results are broadly consistent with the accelerated evolution scenario at z > 8, consistent with that seen in many models.