TY - JOUR
T1 - Testing diagnostics of nuclear activity and star formation in galaxies at z > 1
AU - Trump, Jonathan R.
AU - Konidaris, Nicholas P.
AU - Barro, Guillermo
AU - Koo, David C.
AU - Kocevski, Dale D.
AU - Juneau, Stéphanie
AU - Weiner, Benjamin J.
AU - Faber, S. M.
AU - McLean, Ian S.
AU - Yan, Renbin
AU - Pérez-González, Pablo G.
AU - Villar, Victor
PY - 2013/1/20
Y1 - 2013/1/20
N2 - 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.
AB - 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.
KW - galaxies: Seyfert
KW - galaxies: active
KW - galaxies: fundamental parameters
KW - galaxies: nuclei
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U2 - 10.1088/2041-8205/763/1/L6
DO - 10.1088/2041-8205/763/1/L6
M3 - Article
AN - SCOPUS:84872306679
SN - 2041-8205
VL - 763
JO - Astrophysical Journal Letters
JF - Astrophysical Journal Letters
IS - 1
M1 - L6
ER -