Chemical evolution of high-redshift radio galaxies

被引：0
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作者：
Matsuoka, K. [1 ]
Nagao, T. [1 ,2 ]
Maiolino, R. [3 ]
Marconi, A. [4 ]
Taniguchi, Y. [2 ]
机构：
[1] Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577, Japan
[2] Research Center for Space and Cosmic Evolution, 2-5 Bunkyo-cho, Matsuyama 790-8577, Japan
[3] INAF - Osservatorio Astrofisico di Roma, Via di Frascati 33, 00040 Monte Porzio Catone, Italy
[4] Dipartimento di Astronomia e Scienza Dello Spazio, Universita Degli Studi di Firenze, Largo E. Fermi 2, 50125 Firenze, Italy
来源：
Astronomy and Astrophysics | 2009年 / 503卷 / 03期
关键词：
We present new deep optical spectra of 9 high-z radio galaxies (HzRGs) at z > 2.7 obtained with FORS2 on VLT. These rest-frame ultraviolet spectra are used to infer the metallicity of the narrow-line regions (NLRs) in order to investigate the chemical evolution of galaxies in the high-z universe. We focus mainly on the Civ/He ii and C iii]/Civ flux ratios that are sensitive to both the gas metallicity and ionization parameter. Although the Nv emission has been widely used to infer the gas metallicity; it is often too weak to be measured accurately for NLRs. In combining our new spectra with data from the literature; we examine the possible redshift evolution of the NLR metallicity for 57 HzRGs at 1 z 4. Based on the comparison between the observed emission-line flux ratios and the results of our photoionization model calculations; we find no significant metallicity evolution in NLRs of HzRGs; up to z ∼ 4. Our results imply that massive galaxies had almost completed their chemical evolution at much higher redshift (z > 5). Finally; although we detect strong Nv emission lines in 5 HzRGs at z > 2.7; we point out that high Nv/He ii ratios are not indicative of high metallicities but correspond to high ionization parameters of gas clouds in NLRs. © ESO 2009;
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页码：721 / 730
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