Element Abundances at High Redshifts: The N/O Ratio in a Primeval Galaxy
Element Abundances at High Redshifts: The N/O Ratio in a Primeval Galaxy
复制标题
高红移时的元素丰度：原始星系中的 N/O 比
DOI：
--
复制
发表时间：
1995
期刊：
影响因子：
--
通讯作者：
R. Hunstead
中科院分区：
文献类型：
--
作者：
M. Pettini;K. Lipman;R. Hunstead
在高红移qso光谱中看到的阻尼Lyman α系统提供了确定仍处于早期演化阶段的星系中元素丰度的方法。这些测量最近才得以实现，补充和扩展了对我们银河系中不同恒星群和河外H~II区域的研究所提供的数据，这些数据迄今为止已形成了星系化学演化模型的基础。在本文中，我们用高分辨率的梯级观测证明了这种新方法在明亮的z(em) = 2.940 QSO 2348-147中z(abs) = 2.27936吸收系统中几种元素的潜力。吸收星系似乎是化学上未进化的，重元素丰度只有太阳的1/100；如果它是像我们这样的螺旋星系的祖先，它不太可能在z = 2.3时坍缩形成一个薄盘（对应于在H_0 = 50 km/s/Mpc和q_0 = 0.01时的回看时间约为13 Gyr）。我们的数据使我们能够在金属丰度低于已知最缺乏金属的矮星系的情况下测量氮氧比。我们发现，相对于太阳尺度，N比O至少少15倍。这一结果与目前关于氮的一次生产和二次生产的相对重要性的观点大致一致；未来对几个阻尼Lyman alpha系统的测量将允许对N/O比随时间演变的模型进行更严格的测试。相对于铁，氧和其他α元素的含量不超过3倍，这是银河系盘状和晕状金属贫乏恒星的典型特征。
The damped Lyman alpha systems seen in the spectra of high redshift QSOs offer the means to determine element abundances in galaxies observed while still at an early stage of evolution. Such measurements, which have only recently come within reach, complement and extend the data provided by studies of different stellar populations in our Galaxy and of extragalactic H~II regions which have up to now formed the basis of galactic chemical evolution models. In this paper we demonstrate the potential of this new approach with high-resolution echelle observations of several elements in the z(abs) = 2.27936 absorption system in the bright z(em) = 2.940 QSO 2348-147. The absorbing galaxy appears to be chemically unevolved, with heavy element abundances only 1/100 of solar; if it is the progenitor of a spiral galaxy like our own, it is unlikely to have collapsed to form a thin disk by z = 2.3 (corresponding to a look-back time of approximately 13 Gyr for H_0 = 50 km/s/Mpc and q_0 = 0.01). Our data allow us to measure the nitrogen-to-oxygen ratio at a metallicity lower than those of the most metal-poor dwarf galaxies known. We find that, relative to the solar scale, N is more underabundant than O by at least a factor of 15. This result is broadly in line with current ideas on the relative importance of primary and secondary production of N; future measurements in several damped Lyman alpha systems will permit more stringent tests of models for the evolution of the N/O ratio with time. Oxygen and other alpha-elements are overabundant relative to Fe by no more than the factor of about 3 typical of metal-poor stars in the disk and halo of the Milky Way.