We present Hubble Space Telescope Wide Field Camera 3 slitless grism spectroscopy of 28 emission-line galaxies at z \sim 2 , in the GOODS-S region of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey ( CANDELS ) .
The high sensitivity of these grism observations , with > 1 \sigma detections of emission lines to f > 2.5 \times 10 ^ { -18 }  erg s ^ { -1 }  cm ^ { -2 } , means that the galaxies in the sample are typically \sim 7 times less massive ( median M _ { * } = 10 ^ { 9.5 } M _ { \odot } ) than previously studied z \sim 2 emission-line galaxies .
Despite their lower mass , the galaxies have [ O iii ] /H \beta  ratios which are very similar to previously studied z \sim 2 galaxies and much higher than the typical emission-line ratios of local galaxies .
The WFC3 grism allows for unique studies of spatial gradients in emission lines , and we stack the two-dimensional spectra of the galaxies for this purpose .
In the stacked data the [ O iii ]  emission line is more spatially concentrated than the H \beta  emission line with 98.1 % confidence .
We additionally stack the X-ray data ( all sources are individually undetected ) , and find that the average L _ { [ OIII ] } / L _ { 0.5 - 10 keV } ratio is intermediate between typical z \sim 0 obscured active galaxies and star-forming galaxies .
Together the compactness of the stacked [ O iii ] Â spatial profile and the stacked X-ray data suggest that at least some of these low-mass , low-metallicity galaxies harbor weak active galactic nuclei .