1211.2230 (R. Bouwens et al.)

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    [PDF]

R. Bouwens, L. Bradley, A. Zitrin, D. Coe, M. Franx, W. Zheng, R. Smit, O. Host, M. Postman, L. Moustakas, I. Labbe, M. Carrasco, A. Molino, M. Donahue, D. D. Kelson, M. Meneghetti, S. Jha, N. Benitez, D. Lemze, K. Umetsu, T. Broadhurst, J. Moustakas, P. Rosati, M. Bartelmann, H. Ford, G. Graves, C. Grillo, L. Infante, Y. Jiminez-Teja, S. Jouvel, O. Lahav, D. Maoz, E. Medezinski, P. Melchior, J. Merten, M. Nonino, S. Ogaz, S. Seitz

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 in five near-IR passbands to 1.6 microns, 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 6 sigma detection limit. While we have already reported on the most robust of these candidates, two new z~9 candidates (H~26.2-26.9) are also revealed in our expanded search. The observed H-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 difference 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(-0.15)(+0.30)x that at z~8, ~2x 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. 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.

View original: http://arxiv.org/abs/1211.2230