Discovery of a z = 7.452 High Equivalent Width Lyman-{\alpha} Emitter
  from the Hubble Space Telescope Faint Infrared Grism Survey
  We present the results of an unbiased search for Ly{\alpha} emission from
continuum-selected 6 < z < 8 galaxies. Our dataset consists of 160 orbits of
G102 slitless grism spectroscopy obtained with the Hubble Space Telescope (HST)
Wide Field Camera 3 as part of the Faint Infrared Grism Survey (FIGS; PI:
Malhotra), which obtains deep slitless spectra of all sources in four fields,
and was designed to minimize contamination in observations of
previously-identified high-redshift galaxy candidates. The FIGS data can
potentially spectroscopically confirm the redshifts of galaxies, and as
Ly{\alpha} emission is resonantly scattered by neutral gas, FIGS can also
constrain the ionization state of the intergalactic medium (IGM) during the
epoch of reionization. These data have sufficient depth to detect Ly{\alpha}
emission in this epoch, as Tilvi et al. (2016) have published the FIGS
detection of previously known (Finkelstein et al. 2013) Ly{\alpha} emission at
z = 7.51. The FIGS data use five separate roll-angles of HST to mitigate the
contamination by nearby galaxies. We created a method that accounts for and
removes the contamination from surrounding galaxies, and also removes any
dispersed continuum light from each individual spectrum (Pirzkal et al. 2017).
We searched for significant (> 4{\sigma}) emission lines using two different
automated detection methods, free of any visual inspection biases. Applying
these methods on photometrically-selected high-redshift candidates between 6 <
z < 8 we find two emission lines, one previously published by Tilvi et al.
(2016), and a new line at 1.028{\mu}m. We identify this lines as Ly{\alpha} at
z = 7.452 +/- 0.003. This newly spectroscopically confirmed galaxy has the
highest Ly{\alpha} rest-frame equivalent width (EW Ly{\alpha}) yet published at
z > 7 (140.3 +/- 19.0{\AA}).
