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 sq.arcmin in total area. We have found
three bright Y098-dropouts, which are candidate galaxies at z >~ 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 galaxis (LBGs) observed at lower
redshifts (up to z~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~7.4 is not well explained by the
current luminosity function (LF) estimates at z~8. However, its inferred
surface density could be explained by the prediction from the LFs at z~7 if it
belongs to the high-redshift tail of the galaxy population at z~7.
