A CENSUS OF STAR-FORMING GALAXIES IN THE Z ∼ 9-10 UNIVERSE BASED ON HST plus SPITZER OBSERVATIONS OVER 19 CLASH CLUSTERS: THREE CANDIDATE Z ∼ 9-10 GALAXIES AND IMPROVED CONSTRAINTS ON THE STAR FORMATION RATE DENSITY AT Z ∼ 9.2

We utilize a two-color Lyman-break selection criterion to search for z similar to 9-10 galaxies over the first 19 clusters in the CLASH program. A systematic search yields three z similar to 9-10 candidates. While we have already reported the most robust of these candidates, MACS1149-JD, two additional z similar to 9 candidates are also found and have H-160- band magnitudes of similar to 26.2-26.9. A careful assessment of various sources of contamination suggests less than or similar to 1 contaminants for our z similar to 9-10 selection. To determine the implications of these search results for the luminosity function (LF) and star formation rate density at z similar to 9, we introduce a new differential approach to deriving these quantities in lensing fields. Our procedure is to derive the evolution by comparing the number of z similar to 9-10 galaxy candidates found in CLASH with the number of galaxies in a slightly lower-redshift sample (after correcting for the differences in selection volumes), here taken to be z similar to 8. This procedure takes advantage of the fact that the relative volumes available for the z similar to 8 and z similar to 9-10 selections behind lensing clusters are not greatly dependent on the details of the lensing models. We find that the normalization of the UV LF at z similar to 9 is just 0.28(-0.20)(+0.39) x that at z similar to 8, which is similar to 1.4(-0.8)(+3.0) x lower than extrapolating z similar to 4-8 LF results. While consistent with the evolution in the UV LF seen at z similar to 4-8, these results marginally favor a more rapid evolution at z > 8. Compared to similar evolutionary findings from the HUDF, our result is less insensitive to large-scale structure uncertainties, given our many independent sightlines on the high-redshift universe.