Jonathan R. Trump, Nicholas P. Konidaris, Guillermo Barro, David C. Koo, Dale D. Kocevski, Stephanie Juneau, Benjamin J. Weiner, S. M. Faber, Ian S. McLean, Renbin Yan, Pablo G. Perez-Gonzalez, Victor Villar
We present some of the first science data with the new Keck/MOSFIRE instrument to test the effectiveness of different AGN/SF diagnostics at z~1.5. MOSFIRE spectra were obtained in three H-band multi-slit masks in the GOODS-S field, resulting in two hour exposures of 36 emission-line galaxies. We compare X-ray data with the traditional "BPT" line ratio diagnostics and the alternative mass-excitation and color-excitation diagrams, combining new MOSFIRE infrared data with previous HST/WFC3 infrared spectra (from the 3D-HST survey) and multiwavelength photometry. We demonstrate that a high [OIII]/\Hb ratio is insufficient as an AGN indicator at z>1. For the four X-ray detected galaxies, the classic BPT diagnostic ([OIII]/Hb vs. [NII]/Ha and [SII]/Ha) remains consistent with X-ray AGN/SF classification. The X-ray data also suggest that "composite" galaxies (with intermediate AGN/SF classification) host bona-fide AGNs. Nearly 2/3 of the z~1.5 emission-line galaxies have nuclear activity detected by either X-rays or the BPT diagnostic. Compared to the X-ray and BPT classifications, the mass-excitation method remains effective at z>1, but we show that the color-excitation method requires a new calibration to successfully identify AGNs at these redshifts.
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http://arxiv.org/abs/1212.2218
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