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]/Hβ 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]/Hβ 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.
@article{arxiv.1605.03187,
title = {Disentangling AGN and Star Formation Activity at High Redshift Using Hubble Space Telescope Grism Spectroscopy},
author = {Joanna S. Bridge and Gregory R. Zeimann and Jonathan R. Trump and Caryl Gronwall and Robin Ciardullo and Derek B. Fox and Donald P. Schneider},
journal= {arXiv preprint arXiv:1605.03187},
year = {2016}
}