A Two-Dimensional Spectroscopic Study of Emission Line Galaxies in the
  Faint Infrared Grism Survey (FIGS) I: Detection Method and Catalog
  We present the results from the application of a two-dimensional emission
line detection method, EMission-line two-Dimensional (EM2D), to the
near-infrared G102 grism observations obtained with the Wide-Field Camera 3
(WFC3) as part of the Cycle 22 {\em Hubble Space Telescope} Treasury Program:
the Faint Infrared Grism Survey (FIGS). Using the EM2D method, we have
assembled a catalog of emission line galaxies (ELGs) with resolved star
formation from each of the four FIGS fields. Not only can one better assess the
global properties of ELGs, but the EM2D method allows for the analysis and an
improved study of the individual emission-line region {\it within} each galaxy.
This paper includes a description of the methodology, advantages, and the first
results of the EM2D method applied to ELGs in FIGS. The advantage of 2D
emission line measurements includes significant improvement of galaxy redshift
measurements, approaching the level of accuracy seen in
high-spectral-resolution data, but with greater efficiency; and the ability to
identify and measure the properties of multiple sites of star-formation and
over scales of $\sim$ 1 kpc within individual galaxies out to z $\sim$ 4. The
EM2D method also significantly improves the reliability of high-redshift
($z\sim7$) Lyman-$\alpha$ detections. Coupled with the wide field of view and
high efficiency of space-based grism observations, EM2D provides a noteworthy
improvement on the physical parameters that can be extracted from grism
observations.
