The VIMOS Ultra Deep Survey: Nature, ISM properties, and ionizing spectra of CIII]λ1909 emitters at z = 2-4
The VIMOS Ultra Deep Survey: Nature, ISM properties, and ionizing spectra of CIII]λ1909 emitters at z = 2-4
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VIMOS 超深调查：自然、ISM 特性和 z = 2-4 处 CIII]λ1909 发射体的电离光谱
DOI：
10.1051/0004-6361/201731935
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发表时间：
2018
影响因子：
6.5
通讯作者：
Zucca E.
中科院分区：
文献类型：
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作者：
Nakajima K.;Schaerer D.;Le Fevre O.;Amorin R.;Talia M.;Lemaux B. C.;Tasca L. A. M.;Vanzella E.;Zamorani G.;Bardelli S.;Grazian A.;Guaita L.;Hathi N. P.;Pentericci L.;Zucca E.
目的根据星际介质的主要辐射场和物理条件来解释观测到的遥远星系的紫外光谱。方法我们构建了一个大的光致电离模型网格，并利用CIII 1909、CIV1549的等效宽度(EWS)以及CIII]、CIV和HeII1640复合谱线的线宽比，推导出新的光谱紫外线诊断方法。我们将这些诊断方法应用于之前在VIMOS超深探测中发现的450个CIII]发射星系的样本。结果表明，平均恒星形成星系(EW(CIII)~2A)可以用单星和双星的恒星光电离很好地描述。推测的金属丰度和电离参数通常为Z=0.3-0.5Zsun和logU=-2.7-3，这与以前在类似红移下的工作一致。模型还表明，当前恒星形成开始以来的平均年龄为50-200Myr，电离光子产生率为Log(XIion/[Hzerg])~25.3-25.4。在EW(CIII)=10-20A的源中，约30%可能以活动星系核为主。它们的金属丰度较低，Z=0.02-0.2Zun，电离参数较高(logU=-1.7)。为了解释最强但最稀有的CIII]发射体(EW(CIII)和GT；20A)的平均紫外观测，我们发现恒星的光致电离显然是不够的。一个由年轻恒星群(log(xi_ion/[Hz/erg])~25.7)加上活动星系核组成的辐射场是必需的。此外，对于金属度Z=0.1~0.2ZSun和logU=-1.7~-1.5，需要提高C/O丰度比。结论我们提出的紫外线诊断方法可以作为解释高红移星系观测的重要依据。[节选]
ContextUltraviolet (UV) emission-line spectra are used to spectroscopically confirm high-z galaxies and increasingly also to determine their physical properties.AimsTo interpret the observed UV spectra of distant galaxies in terms of the dominant radiation field and the physical condition of the interstellar medium.MethodsWe construct a large grid of photoionization models and derive new spectral UV line diagnostics using equivalent widths (EWs) of CIII]1909, CIV1549 and the line ratios of CIII], CIV, and HeII1640 recombination lines. We apply these diagnostics to a sample of 450 CIII]-emitting galaxies at z=2-4 previously identified in the VIMOS Ultra Deep Survey.ResultsWe show that the average star-forming galaxy (EW(CIII])~2A) is well described by stellar photoionization from single and binary stars. The inferred metallicity and ionization parameter is typically Z=0.3-0.5Zsun and logU=-2.7 to -3, in agreement with earlier works at similar redshifts. The models also indicate an average age of 50-200Myr since the beginning of the current star-formation, and an ionizing photon production rate, xi_ion, of log(xi_ion/[Hz/erg])~25.3-25.4. Among the sources with EW(CIII])=10-20A, ~30% are likely dominated by AGNs. Their derived metallicity is low, Z=0.02-0.2Zsun, and the ionization parameter higher (logU=-1.7). To explain the average UV observations of the strongest but rarest CIII] emitters (EW(CIII])>20A), we find that stellar photoionization is clearly insufficient. A radiation field consisting of a mix of a young stellar population (log(xi_ion/[Hz/erg])~25.7) plus an AGN component is required. Furthermore an enhanced C/O abundance ratio is needed for metallicities Z=0.1-0.2Zsun and logU=-1.7 to -1.5.ConclusionsThe UV diagnostics we propose should serve as an important basis for the interpretation of observations of high-redshift galaxies. [abridged]