Inversion of the Lyman α forest: three-dimensional investigation of the intergalactic medium
Inversion of the Lyman α forest: three-dimensional investigation of the intergalactic medium
复制标题
莱曼α森林的反演：星际介质的三维研究
DOI：
--
复制
发表时间：
2001
期刊：
影响因子：
--
通讯作者：
P. Petitjean
中科院分区：
文献类型：
--
作者：
C. Pichon;J. Vergely;E. Rollinde;S. Colombi;P. Petitjean
我们讨论贝叶斯反演方法的实施，以便从高红移类星体光谱（所谓的莱曼 α 森林）中观察到的中性氢莱曼 α 吸收的观测中恢复星系间介质的特性。我们使用两种互补方案：（i）约束高斯随机场线性方法，以及（ii）更通用的非线性显式贝叶斯反卷积方法，该方法特别提供了约束气体状态方程参数的可能性。
在可忽略的测量误差、低分辨率光谱和零均值先验的限度内，第一种方法的插值能力与第二种方法相当。
在依赖于两点相关函数的先验假设的同时，我们展示了如何通过反转相邻的低分辨率视线的合适网络来至少定性地恢复红移空间中大规模结构的三维拓扑。使用专门为解决此问题而设计的 N 体模拟，在规则的视线束上对这些方法进行了测试。
我们还讨论了在高光谱分辨率下观察到的单视线的反演。我们的初步研究表明，当红移畸变的影响可以忽略不计时，显式贝叶斯方法可用于得出气体物理状态的定量信息。光谱中的信息相对于描述气体状态方程的两个参数（温度比例因子和多变指数）仍然是简并的。
通过同时约束重建实空间中的速度场和密度场来考虑红移失真，同时假设两个场之间存在统计相关性。该方法似乎在强先验条件下运行良好，其中假定奇特速度是密度场中最有可能实现的。最后，我们研究了视线分离和视线数量的影响。我们的分析表明，多个低分辨率视线可用于改善高分辨率视线上最可能的速度重建。
We discuss the implementation of Bayesian inversion methods in order to recover the properties of the intergalactic medium from observations of the neutral hydrogen Lyman α absorptions observed in the spectra of high-redshift quasars (the so-called Lyman α forest). We use two complementary schemes: (i) a constrained Gaussian random field linear approach, and (ii) a more general non-linear explicit Bayesian deconvolution method, which offers in particular the possibility to constrain the parameters of the equation of state for the gas.
The interpolation ability of the first approach is shown to be equivalent to the second one in the limit of negligible measurement errors, low-resolution spectra and null mean prior.
While relying on prior assumption for the two-point correlation functions, we show how to recover, at least qualitatively, the three-dimensional topology of the large-scale structures in redshift space by inverting a suitable network of adjacent, low-resolution lines of sight. The methods are tested on regular bundles of lines of sight using N-body simulations specially designed to tackle this problem.
We also discuss the inversion of single lines of sight observed at high spectral resolution. Our preliminary investigations suggest that the explicit Bayesian method can be used to derive quantitative information on the physical state of the gas when the effects of redshift distortion are negligible. The information in the spectra remains degenerate with respect to two parameters (the temperature scale factor and the polytropic index) describing the equation of state of the gas.
Redshift distortion is considered by simultaneous constrained reconstruction of the velocity and the density field in real space, while assuming statistical correlation between the two fields. The method seems to work well in the strong prior regime where peculiar velocities are assumed to be the most likely realization in the density field. Finally, we investigate the effect of line-of-sight separation and number of lines of sight. Our analyses suggest that multiple low-resolution lines of sight could be used to improve the most likely velocity reconstruction on a high-resolution line of sight.