| タイトル | Quiescent Galaxies in the 3D-HST Survey: Spectroscopic Confirmation of a Large Number of Galaxies with Relatively Old Stellar Populations at Z approx. 2 |
| 本文（外部サイト） | http://hdl.handle.net/2060/20140016558 |
| 著者（英） | Tease, Katherine Whitaker; Nelson, Erica J.; Brammer, Gabriel; VanDokkum, Pieter G.; Lundgren, Britt F.; Kriek, Mariska; Momcheva, Ivelina G.; Rix, Hans-Walter; Franx, Marijn; Skelton, Rosalind; Fumagalli, Mattia; Patel, Shannon G.; Labbe, Ivo |
| 著者所属（英） | NASA Goddard Space Flight Center |
| 発行日 | 2013-06-10 |
| 言語 | eng |
| 内容記述 | Quiescent galaxies at zeta approximately 2 have been identified in large numbers based on rest-frame colors, but only a small number of these galaxies have been spectroscopically confirmed to show that their rest-frame optical spectra show either strong Balmer or metal absorption lines. Here, we median stack the rest-frame optical spectra for 171 photometrically quiescent galaxies at 1.4 less than z less than 2.2 from the 3D-HST grism survey. In addition to H(Beta) (lambda 4861 Angstroms), we unambiguously identify metal absorption lines in the stacked spectrum, including the G band (lambda 4304 Angstroms), Mg I (lambda 5175 Angstroms), and Na i (lambda 5894 Angstroms). This finding demonstrates that galaxies with relatively old stellar populations already existed when the universe was approximately 3 Gyr old, and that rest-frame color selection techniques can efficiently select them. We find an average age of 1.3(+0.1/0.3) Gyr when fitting a simple stellar population to the entire stack. We confirm our previous result from medium-band photometry that the stellar age varies with the colors of quiescent galaxies: the reddest 80% of galaxies are dominated by metal lines and have a relatively old mean age of 1.6(+0.5/0.4) Gyr, whereas the bluest (and brightest) galaxies have strong Balmer lines and a spectroscopic age of 0.9(+0.2/0.1) Gyr. Although the spectrum is dominated by an evolved stellar population, we also find [O III] and H emission. Interestingly, this emission is more centrally concentrated than the continuum with L(sub OIII) = 1.7 +/- 0.3 10(exp 40 erg s1, indicating residual central star formation or nuclear activity. |
| NASA分類 | Astrophysics |
| レポートNO | GSFC-E-DAA-TN8478 |
| 権利 | Copyright, Distribution under U.S. Government purpose rights |
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