We present the first results on the search for very bright (M_AB -21) galaxies at redshift z~8 from the Brightest of Reionizing Galaxies (BoRG) survey. BoRG is a Hubble Space Telescope Wide Field Camera 3 pure-parallel survey that is obtaining images
on random lines of sight at high Galactic latitudes in four filters (F606W, F098M, F125W, F160W), with integration times optimized to identify galaxies at z>7.5 as F098M-dropouts. We discuss here results from a search area of approximately 130 arcmin^2 over 23 BoRG fields, complemented by six other pure-parallel WFC3 fields with similar filters. This new search area is more than two times wider than previous WFC3 observations at z~8. We identify four F098M-dropout candidates with high statistical confidence (detected at greater than 8sigma confidence in F125W). These sources are among the brightest candidates currently known at z~8 and approximately ten times brighter than the z=8.56 galaxy UDFy-38135539. They thus represent ideal targets for spectroscopic followup observations and could potentially lead to a redshift record, as our color selection includes objects up to z~9. However, the expected contamination rate of our sample is about 30% higher than typical searches for dropout galaxies in legacy fields, such as the GOODS and HUDF, where deeper data and additional optical filters are available to reject contaminants.
We report on the discovery of three bright, strongly-lensed objects behind Abell 1703 and CL0024+16 from a dropout search over 25 square arcminutes of deep NICMOS data, with deep ACS optical coverage. They are undetected in the deep ACS images below
8500 A and have clear detections in the J and H bands. Fits to the ACS, NICMOS and IRAC data yield robust photometric redshifts in the range z~6-7 and largely rule out the possibility that they are low-redshift interlopers. All three objects are extended, and resolved into a pair of bright knots. The bright i-band dropout in Abell 1703 has an H-band AB magnitude of 23.9, which makes it one of the brightest known galaxy candidates at z>5.5. Our model fits suggest a young, massive galaxy only ~ 60 million years old with a mass of ~ 1E10 solar mass. The dropout galaxy candidates behind CL0024+16 are separated by 2.5 (~ 2 kpc in the source plane), and have H-band AB magnitudes of 25.0 and 25.6. Lensing models of CL0024+16 suggest that the objects have comparable intrinsic magnitudes of AB ~ 27.3, approximately one magnitude fainter than L* at z~6.5. Their similar redshifts, spectral energy distribution, and luminosities, coupled with their very close proximity on the sky, suggest that they are spatially associated, and plausibly are physically bound. Combining this sample with two previously reported, similarly magnified galaxy candidates at z~6-8, we find that complex systems with dual nuclei may be a common feature of high-redshift galaxies.
