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 VizJH Attenuated Spectrum Unattenuated Spectrum No detection Blue continuum Star-forming galaxies are relatively bright in the rest-frame UV (O & B stars) Redshift: Their spectra are shifted to the red (longer wavelengths) due to cosmological expansion: Intervening Hydrogen attenuates the UV spectrum creating a sharp featured called the Lyman break λ obs = λ em (z + 1)

5. Lyman Break Color Selection Rest-frame UV Continuum Color Lyman Break Color Low-mass stars (M, L, T- dwarfs): exclude point sources in z 850 z~7 (z- dropouts) Bouwens et al. 2008

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

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

8. 3.4 x 3.4 arcmin WFC3/IR vs. NICMOS/NIC3 ACS/WFC 2.2 x 2.2 arcmin WFC3/IR NIC3 WFC3/IR is ~6x larger in area than NICMOS and has much higher sensitivity WFC3/IR has a discovery efficiency ~30-40x NICMOS NICMOS required ~100 orbits to find one z ~ 7 galaxy, but it takes WFC3/IR only a few orbits! z ~ 7 galaxy comparisons WFC3/IR NICMOS/NIC3 2.2” x 2.2” cutouts Bouwens et 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, H 160 ~ 24.0 AB! (brightest z 850 - dropout candidate known) A1703-zD6 spectroscopically confirmed at z = 7.045 (z phot = 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 F125W F160W F814W F775W

15. More Candidates in Cluster Fields? OrbitsZ~7 Candidates CLASH50~10 HIPPIES1303 UDF9616

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