We present long-slit NIR spectra, obtained using the ISAAC instrument at the Very Large Telescope, for nine radio galaxies at z~2.5. One-dimensional spectra have been extracted and cross calibrated with optical spectra from the literature to produce line spectra spanning a rest wavelength of ~1200-7000 A. We have also produced a composite of the rest-frame UV-optical line fluxes of powerful, z~2.5 radio galaxies. We have investigated the relative strengths of Ly-alpha, H-beta, H-alpha, HeII 1640 and HeII 4687, and we find that Av can vary significantly from object to object. In addition, we identify new line ratios to calculate electron temperature: [NeV] 1575/[NeV] 3426, [NeIV] 1602/[NeIV] 2423, OIII] 1663/[OIII] 5008 and [OII] 2471/[OII]3728. We model the emission line spectra and conclude they are best explained by AGN-photoionization with the ionization parameter U varying between objects. Single slab photoionization models are unable to reproduce the high- and the low-ionization lines simultaneously: this may be alleviated either by combining two or more single slab photoionization models with different U, or by using mixed-medium models such as those of Binette, Wilson & Storchi-Bergmann (1996). On the basis of NV/NIV] and NIV]/CIV we argue that shocks make a fractional contribution to the ionization of the EELR. We find that in the EELR of z~2 radio galaxies the N/H abundance ratio is close to its solar value. We conclude that N/H and metallicity do not vary by more than a factor of two in our sample. This is consistent with the idea that massive ellipticals are assembled very early in the history of the universe, and then evolve relatively passively up to the present day.
Gas metallicity diagnostics in star-forming galaxies
一般来说，遥远星系中的气体金属丰度只能通过几条显著的发射线来推断。各种理论模型已被用来预测发射线通量和金属丰度之间的关系，这表明一些线比可以用来诊断气体金属丰度的星系。然而，准确的经验校准这些发射线通量比从真正的星系光谱跨越广泛的金属丰度范围仍然缺乏。在本文中，我们提供了这样的经验校准通过使用两组光谱数据的组合：一组由低金属量星系与测量的[OIII]4363，和其他一个组成的星系在SDSS DR 4的金属量已确定从各种强发射线在其光谱。这一综合数据集构成了迄今为止最大的星系样本，其中包含有关气体金属丰度的信息，涵盖了最广泛的金属丰度范围。我们的经验图表明，线比[OIII]/[OII]是一个有用的工具，打破退化的R_23参数时，没有信息的[NII]线。线比[NeIII]/[OII]的结果也是一个有用的高z星系的金属丰度指标。最后，我们比较这些经验关系与光电离模型。我们发现经验的R_23-金属丰度序列与常数电离参数模型所预期的趋势有很大的差异，这可以解释为星系中平均电离参数对金属丰度有很强的依赖性。这一结果应该警告使用恒定电离参数的理论模型来推断金属丰度从观察到的线比。（略）
GALEX UV Color Relations for Nearby Early-Type Galaxies
我们使用GALEX/光学光度学来构建颜色的颜色关系的早期类型的星系按形态类型排序。我们匹配了GALEX GR 1公开发布版和第一个IR1.1内部发布版中的天体，其中RC 3早型星系的形态类型为-5.5<T<-1.5，平均误差为T<1.5，平均误差为（B-V）T<0.05。在对每个匹配进行目视检查后，我们剩下130个星系，它们在远紫外和近紫外波段具有可靠的GALEX管道测光。该样本分为椭圆形（-5.5<T<-3.5）和透镜形（-3.5<T<-1.5）。在对银河系消光进行校正后，绘制了两个子样本的FUV-NUV与（B-V）_{Tc}的色-色图。我们发现椭圆星系的FUV-NUV和（B-V）_{Tc}颜色之间存在着紧密的反相关关系，当（B-V）_{Tc}变红时，UV颜色变蓝。这种关系很可能是颜色-金属丰度关系到GALEX NUV波段的延伸。我们怀疑，相关性的主要来源是在NUV波段的金属线覆盖。透镜星系的FUV-NUV与B-V相关性有较大的散射，我们推测这反映了低水平恒星形成的存在。如果后面的天体（即那些在FUV-NUV和B-V中都是蓝色的天体）被解释为具有最近的恒星形成活动，那么这将是几个百分比（~4%）的椭圆星系和~15%的透镜星系的情况;这将使我们130个早期星系的完整样本中约有10%的早期星系具有剩余的恒星形成。我们还绘制了FUV-NUV与Mg_2指数和中心速度色散的关系曲线。我们发…
