Testing diagnostics of nuclear activity and star formation in galaxies at z > 1



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Trump, Jonathan R. and Konidaris, Nicholas P. and Barro, Guillermo and Koo, David C. and Kocevski, Dale D. and Juneau, Stephanie and Weiner, Benjamin J. and Faber, S. M. and McLean, Ian S. and Yan, Renbin and Pérez González, Pablo Guillermo and Villar, Victor (2013) Testing diagnostics of nuclear activity and star formation in galaxies at z > 1. Astrophysical journal letters, 763 (1). ISSN 2041-8205

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Official URL: http://dx.doi.org/10.1088/2041-8205/763/1/L6


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 2 hr exposures of 36 emission-line galaxies. We compare X-ray data with the traditional emission-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 [O III]/Hβ ratio is insufficient as an active galactic nucleus (AGN) indicator at z > 1. For the four X-ray-detected galaxies, the classic diagnostics ([O III]/Hβ versus [N II]/Hα and [S II]/Hα) remain 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 classic diagnostics. Compared to the X-ray and line ratio 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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© 2013 The American Astronomical Society. All rights reserved.
Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555. Also based on data obtained at the W. M. Keck Observatory, made possible by the generous financial support of the W. M. Keck Foundation and operated as a scientific partnership among Caltech, the University of California, and NASA. J.R.T. and the authors from UCSC acknowledge support from NASA HST grants GO-12060.10-A and AR-12822.03, Chandra grant G08-9129A, and NSF grant AST-0808133. N.P.K. acknowledges support from NSF grant AST-1106171. This work uses data from the 3-D HST Treasury Survey (Program ID 12177). We owe tremendous gratitude to the MOSFIRE commissioning team for development and support of a spectacular instrument. We also thank Greg Wirth, Marc Kassis, Jim Lyke, and the staff of Keck observatory for excellent support while observing. We wish to recognize and acknowledge the very significant cultural role that the summit of Mauna Kea has within the indigenous Hawaiian community: we are fortunate to have the opportunity to conduct observations from this mountain.

Uncontrolled Keywords:High-redshift galaxies; Digital sky survey; Mass-metallicity relation; Emission-line galaxies; Galactic nuclei; Forming galaxies; Host galaxies; Stellar mass; Black-holes; X-ray
Subjects:Sciences > Physics > Astrophysics
Sciences > Physics > Astronomy
ID Code:38433
Deposited On:06 Jul 2016 16:52
Last Modified:10 Dec 2018 15:05

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