arXiv:1211.2230v2 [astro-ph.CO] 12 Nov 2012 Draft version November 13, 2012 Preprint typeset using L A T E X style emulateapj v. 5/2/11 A CENSUS OF STAR-FORMING GALAXIES IN THE Z ∼ 9-10 UNIVERSE BASED ON HST+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 1 R. J. Bouwens 2,3 , L. Bradley 4 , A. Zitrin 5 , D. Coe 4 , M. Franx 2 , W. Zheng 6 , R. Smit 2 , O. Host 7 , M. Postman 4 , L. Moustakas 8 , I. Labb´ e 2 , M. Carrasco 5,9 , A. Molino 10 , M. Donahue 11 , D.D. Kelson 12 , M. Meneghetti 13 , S. Jha 14 , N. Ben´ ıtez 10 , D. Lemze 6 , K. Umetsu 15 , T. Broadhurst 16 , J. Moustakas 17,18 , P. Rosati 19 , S. Jouvel 20 , M. Bartelmann 5 , H. Ford 6 , G. Graves 21 , C. Grillo 22 , L. Infante 9 , Y. Jimenez-Teja 10 , O. Lahav 20 , D. Maoz 23 , E. Medezinski 6 , P. Melchior 24 , J. Merten 8 , M. Nonino 25 , S. Ogaz 4 , S. Seitz 26 Draft version November 13, 2012 ABSTRACT We utilise a two-color Lyman-Break selection criterion to search for z ∼ 9-10 galaxies over the first 19 clusters in the CLASH program. Key to this search are deep observations over our clusters in five near-IR passbands to 1.6µm, allowing us good constraints on the position of the Lyman break to z ∼ 10. A systematic search yields three z ∼ 9-10 candidates in total above a 6σ detection limit. While we have already reported the most robust of these candidates, MACS1149-JD, in a previous publication, two additional z ∼ 9 candidates are also revealed in our expanded search. The new candidates have H 160 -band AB magnitudes of ∼26.2-26.9 and are located behind MACSJ1115.9+0129 and MACSJ1720.3+3536. The observed H 160 - Spitzer/IRAC colors for the sources are sufficiently blue to strongly favor redshifts of z ≥ 9 for these sources. A careful assessment of various sources of contamination suggests 1 contaminants for our z ∼ 9-10 selection. To determine the implications of these search results for the LF and SFR density at z ∼ 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 ∼ 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 ∼ 8. This procedure takes advantage of the fact that the relative selection volumes available for the z ∼ 8 and z ∼ 9-10 selections behind lensing clusters are not greatly dependent on the details of the gravitational lensing models. We find that the normalization of the UV LF at z ∼ 9 is just 0.22 +0.30 −0.15 × that at z ∼ 8, ∼2 +3 −1 × lower than what we would infer extrapolating z ∼ 4-8 LF results. These results therefore suggest a more rapid evolution in the UV LF at z> 8 than seen at lower redshifts (although the current evidence here is weak). Compared to similar evolutionary findings from the HUDF, our result is much more insensitive to large-scale structure uncertainties, given our many independent sightlines on the high-redshift universe. Subject headings: galaxies: evolution — galaxies: high-redshift 1 Based on observations made with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Uni- versities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. 2 Leiden Observatory, Leiden University 3 University of California, Santa Cruz 4 Space Telescope Science Institute 5 Universitat Heidelberg 6 The Johns Hopkins University 7 Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen 8 JPL, California Institute of Technology 9 Universidad Catolica de Chile 10 Instituto de Astrof´ ısica de Andaluc´ ıa 11 Michigan State University 12 The Carnegie Institute for Science; Carnegie Observatories 13 INAF, Osservatorio Astronomico di Bologna 14 Rutgers University 15 Academia Sinica, Institute of Astronomy & Astrophysics 16 University of the Basque Country 17 University of California, San Diego 18 Siena College 19 European Southern Observatory 20 University College London 21 University of California, Berkeley 22 Technische Universitat Munchen 23 Tel Aviv University 24 The Ohio State University 25 INAF, Osservatorio Astronomico di Trieste 26 Universitas Sternwarte, M¨ unchen