The nature of NV absorbers at high redshift
The nature of NV absorbers at high redshift
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DOI：
10.1051/0004-6361/200810421
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发表时间：
2008-07
影响因子：
6.5
通讯作者：
C. Fechner;P. Richter
中科院分区：
文献类型：
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作者：
C. Fechner;P. Richter
目标。本文根据VLT/UVES仪器获得的数据，研究了19个类星体光谱中1.5 z 2.5处的Nv吸收系统。我们的分析既包括来自星系际介质的吸收体，也包括背景类星体附近的系统。方法.我们建立了详细的光电离模型来研究吸收体中的物理条件和丰度，并限制电离辐射的光谱硬度。结果介入Nv分量的发生率为dN/dz = 3.38 ± 0.43，对应于dN/dX = 1.10 ± 0.14。柱密度分布函数由斜率β = 1.89 ± 0.22拟合，与C iv和O vi的测量结果一致。窄线宽（bNv 6 k m s-1）意味着光电离而不是碰撞作为主要电离过程。Civ和Nv的柱密度是相关的，但对于介入和缔合吸收体显示不同的斜率，这表明不同的电离光谱。相关联的系统被发现更富含金属，密度更大，更紧凑，比介入吸收。该结论与所采用的电离辐射无关。对于介于其间的N v系统，我们发现典型值为[C/H]<$− 0.6和nH <$10 −3.6 cm −3，尺寸为几个kpc，而对于相关的N v吸收体，我们得到[C/H]<$+0.7，nH <$10 −2.8 cm −3和尺寸为几个10 pc。氮相对碳的丰度[N/C]和氧、硅等α元素的丰度[N/α ]与[N/H]相关，表明次生氮的富集。介入系统中[N/α]的较大分散表明IGM的不均匀富集。[N/α ]和[α/C]之间存在反相关，可以用来约束产生碳和氮的恒星群体的初始质量函数。
Aims. We present a study of N v absorption systems at 1.5 z 2.5 in the spectra of 19 QSOs, based on data obtained with the VLT/UVES instrument. Our analysis includes both the absorbers arising from the intergalactic medium, as well as systems in the vicinity of the background quasar. Methods. We construct detailed photoionization models to study the physical conditions and abundances in the absorbers and to constrain the spectral hardness of the ionizing radiation. Results. The rate of incidence for intervening N v components is dN/dz = 3.38 ± 0.43, corresponding to dN/dX = 1.10 ± 0.14. The column density distribution function is fitted by the slope β = 1.89 ± 0.22, consistent with measurements of C iv and O vi .T he narrow line widths (bNv ∼ 6k m s −1 ) imply photoionization rather than collisions as the dominating ionization process. The column densities of C iv and N v are correlated but show different slopes for intervening and associated absorbers, which indicates different ionizing spectra. Associated systems are found to be more metal-rich, denser, and more compact than intervening absorbers. This conclusion is independent of the adopted ionizing radiation. For the intervening N v systems we find typical values of [C/H] ∼− 0.6 and nH ∼ 10 −3.6 cm −3 and sizes of a few kpc, while for associated N v absorbers we obtain [C/H] ∼ +0.7, nH ∼ 10 −2.8 cm −3 and sizes of several 10 pc. The abundance of nitrogen relative to carbon [N/C] and α-elements like oxygen and silicon [N/α ]i s correlated with [N/H], indicating the enrichment by secondary nitrogen. The larger scatter in [N/α] in intervening systems suggests an inhomogeneous enrichment of the IGM. There is an anti-correlation between [N/α ]a nd [α/C], which could be used to constrain the initial mass function of the carbon- and nitrogen-producing stellar population.