Testing Diagnostics of Nuclear Activity and Star Formation in Galaxies at z>1
Jonathan R. Trump (1), Nicholas P. Konidaris (2), Guillermo Barro (1), David C. Koo (1), Dale D. Kocevski (3), Stephanie Juneau (4), Benjamin J. Weiner (5), S. M. Faber (1), Ian S. McLean (6), Renbin Yan (3), Pablo G. Perez-Gonzalez (7), Victor Villar (7)
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.
Lessons from cosmic history: The case for a linear star formation — H2 relation
Observations show that star formation in galaxies is closely correlated with the abundance of molecular hydrogen. Modeling this empirical relation from first principles proves challenging, however, and many question regarding its properties remain open. For instance, the exact functional form of the relation is still debated and it is also unknown whether it applies at z>4, where CO observations are sparse. Here, we analyze how the shape of the star formation