0 Assigned ID: 1700 ----- Attempting Submission 1 (Fri Mar 01 19:55:33 GMT 2013) ----- HST Phase I Proposal 1700 (hstff_cy21.apt) successfully submitted. ----- Attempting Submission 2 (Fri Mar 01 23:19:57 GMT 2013) ----- HST Phase I Proposal 1700 (hstff_cy21.apt) successfully submitted. ----- Attempting Submission 3 (Sat Mar 02 00:58:50 GMT 2013) ----- Understanding the evolution of early galaxies and their contribution to reionization has been a longstanding goal of observational astronomy. Hubble's WFC3/IR camera has revolutionized our knowledge of 7<z<8 galaxies, but we still know very little about z>~8 galaxies due to their faint luminosities (M*>~-20.3) and low volume densities. In particular, blank-field studies suggest a very dramatic buildup in cosmic star-formation rate density (SFRD) in the ~165 Myr between z~8-10. These results are in tension with lensed-field studies which suggest a smooth buildup of galaxies from z ~ 10 to 4. To distinguish between these scenarios, deeper observations are required to increase z > 9 number statistics and to reduce the significant cosmic variance due to a single blank field with sufficient depth (UDF + surrounding regions). The upcoming HST Frontier Fields (HSTFF) program will obtain ultra deep observations of both "blank" and cluster-lensed fields. The latter are more efficient for high-z searches but introduce magnification uncertainties which we have quantified and found to be subdominant to Poisson uncertainties. Based on the archival first-year HSTFF data, we will identify a large sample of ~35-54 galaxies at 8<z<12, enabling us to distinguish between the possible extremes in z>9 galaxy evolution and placing new constraints on reionization. Additionally, we will measure the rest-frame UV continuum slopes of z~6-8 galaxies to improve dust extinction estimates at high redshift, a key ingredient in SFRD measurements. We will also perform strong lensing analyses to produce some of the highest resolution cluster dark matter maps to date. COSMOLOGY Default Medium false false false false false SUPPORTED