PROBING VERY BRIGHT END OF GALAXY LUMINOSITY FUNCTION AT z ≳ 7 USING HUBBLE SPACE TELESCOPE PURE PARALLEL OBSERVATIONS

We report the first results from the Hubble Infrared Pure Parallel Imaging Extragalactic Survey, which utilizes the pure parallel orbits of the Hubble Space Telescope to do deep imaging along a large number of random sightlines. To date, our analysis includes 26 widely separated fields observed by the Wide Field Camera 3, which amounts to 122.8 arcmin(2) in total area. We have found three bright Y-098-dropouts, which are candidate galaxies at z greater than or similar to 7.4. One of these objects shows an indication of peculiar variability and its nature is uncertain. The other two objects are among the brightest candidate galaxies at these redshifts known to date (L > 2L*). Such very luminous objects could be the progenitors of the high-mass Lyman break galaxies observed at lower redshifts (up to z similar to 5). While our sample is still limited in size, it is much less subject to the uncertainty caused by cosmic variance than other samples because it is derived using fields along many random sightlines. We find that the existence of the brightest candidate at z approximate to 7.4 is not well explained by the current luminosity function (LF) estimates at z approximate to 8. However, its inferred surface density could be explained by the prediction from the LFs at z approximate to 7 if it belongs to the high-redshift tail of the galaxy population at z approximate to 7.