  Differentiating between active galactic nuclei (AGN) activity and star
formation in z ~ 2 galaxies is difficult because traditional methods, such as
line ratio diagnostics, change with redshift while multi-wavelength methods
(X-ray, radio, IR) are sensitive to only the brightest AGN. We have developed a
new method for spatially resolving emission lines in HST/WFC3 G141 grism
spectra and quantifying AGN activity through the spatial gradient of the [O
III]/H$\beta$ line ratio. Through detailed simulations, we show that our novel
line-ratio gradient approach identifies ~ sim 40% more low-mass and obscured
AGN than obtained by classical methods. Based on our simulations, we developed
a relationship that maps stellar mass, star formation rate, and measured [O
III]/H$\beta$ gradient to AGN Eddington ratio. We apply our technique to
previously studied stacked samples of galaxies at z ~2 and find that our
results are consistent with these studies. Using this gradient method will also
be able to inform other galaxy evolution science, such as inside-out quenching
and metallicity gradients, and will be widely applicable to future spatially
resolved JWST data.
