1. High-Redshift Galaxies in Cluster Fields Wei Zheng, Larry Bradley, and the CLASH high-z search group

2. High-Redshift Galaxies Key Science Questions: • How do the first generations of galaxies build up and evolve at the earliest times? • Number densities, sizes/morphologies, UV slopes, brightness distribution (UVLF), star-formation rates, masses, ages, metallicities • How do these quantities change with cosmic time (e.g. N(z), L(z), SFR(z), M(z))? • What are their stellar populations and how do they evolve: unique conditions in the early universe (e.g. low metallicities, no dust, top-heavy IMF)? • What is the contribution of star-forming galaxies to reionization?

3. Galaxy Clusters as Cosmic Telescopes Strong Lensing Basics: • Galaxy cluster mass density deforms local space-time • Pure geometrical effect with no dependence on photon energy • Provides large areas of high magnification (μ ~ 10) • Amplifies both galaxy flux and size while conserving surface brightness • Can have multiply-imaged background galaxies Predicted by Einstein in 1915 (GR) Observationally confirmed by Eddington during the 1919 solar eclipse

4. Lyman Break “Dropout” Technique Star-forming galaxies are relatively bright in the rest-frame UV (O & B stars) Unattenuated Spectrum Intervening Hydrogen attenuates the UV spectrum creating a sharp featured called the Lyman break Attenuated Spectrum Redshift: Their spectra are shifted to the red (longer wavelengths) due to cosmological expansion: λobs = λem (z + 1) V i z J H No detection Blue continuum

5. Lyman Break Color Selection z~7 (z-dropouts) Low-mass stars (M, L, T-dwarfs): exclude point sources in z850 Lyman Break Color Rest-frame UV Continuum Color Bouwens et al. 2008

6. LBG at z ~ 7.6 ± 0.4 HAB = 24.7 (observed) HAB = 27.1 (intrinsic)

7. NASA, Bradley et al. STScI PRC08-08a

8. WFC3/IR vs. NICMOS/NIC3 WFC3/IR is ~6x larger in area than NICMOS and has much higher sensitivity ACS/WFC WFC3/IR NIC3 2.2 x 2.2 arcmin NICMOS required ~100 orbits to find one z ~ 7 galaxy, but it takes WFC3/IR only a few orbits! 3.4 x 3.4 arcmin WFC3/IR has a discovery efficiency ~30-40x NICMOS z ~ 7 galaxy comparisons WFC3/IR NICMOS/NIC3 2.2” x 2.2” cutouts Bouwenset al. 2010

9. WFC3/IR Bright Lensed z-dropouts • Abell 1703: 1 orbit each in WFC3/IR F125W (J) and F160W (H) • 8 z-dropout candidates! (some may be multiply-imaged) • μ~ 3 - 40 Bradley et al. 2011 (arXiv1104.2035B)

10. WFC3/IR Bright Lensed z-dropouts • Brightest candidate: z ~ 6.7, H160 ~ 24.0 AB! (brightest z 850-dropout candidate known) • A1703-zD6 spectroscopically confirmed at z = 7.045 (zphot = 7.0) (Schenker et al. 2011, arXiv1107.1251S) Bradley et al. 2011 (arXiv1104.2035B)

11. Abell 2261 AB~25.5

12. Another Dropout Candidate in Abell 2261 that Shows Multiple Components

13. Dropout Candidate in MS2137

14. MACS0744 F814W F775W F125W F160W

15. More Candidates in Cluster Fields?

16. Summary • We have found ~10 candidates at z~7 • One or two of them are marginally bright (AB~25) • Work in progress towards fainter candidates • Many of the candidates display multiple components • Finding opportunity high inhomogeneous among clusters • Many more red objects. Spitzer data important