X-ray absorption of cold gas: Simulating interstellar molecular clouds in the laboratory,Physical Review E

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X-ray absorption of cold gas: Simulating interstellar molecular clouds in the laboratory
Physical Review E ( IF 2.2 ) Pub Date : 2021-07-13 , DOI: 10.1103/physreve.104.015205
I Gissis ₁ , A Fisher ₁ , E Behar ₁

Affiliation

Galactic and extragalactic sources produce x-rays that are often absorbed by molecules and atoms in giant molecular clouds (GMCs), which provides valuable information about their composition and physical state. We mimic this phenomenon with a laboratory Z-pinch x-ray source, which is impinged on neutral molecular gas. This technique produces a soft x-ray pseudocontinuum using a pulsed-current generator. The absorbing gas is injected from a 1-cm-long planar gas-puff without any window or vessel along the line of sight. An x-ray spectrometer with a resolving power of

λ / Δ λ \sim 420

, comparable to that of astrophysical space instruments, records the absorbed spectra. This resolution clearly resolves the molecular lines from the atomic lines, thus motivating the search for a molecular signature in astrophysical x-ray spectra. The experimental setup enables different gas compositions and column densities.

K

-shell spectra of

{CO}_{2}, N_{2}

, and

O_{2}

reveal a plethora of absorption lines and photoelectric edges measured at molecular column densities between

\sim 10^{16}

and

10^{18}

{cm}^{- 2}

typical of GMCs. We find that the population of excited states, contributing to the edge, increases with gas density.

中文翻译：

冷气体的 X 射线吸收：在实验室模拟星际分子云

银河和河外源产生的 X 射线通常被巨分子云 (GMC) 中的分子和原子吸收，这提供了有关其组成和物理状态的宝贵信息。我们用实验室中的 Z-pinch X 射线源模拟了这种现象，它撞击中性分子气体。该技术使用脉冲电流发生器产生软 X 射线伪连续谱。吸收气体从一个 1 厘米长的平面气体喷射器中注入，沿视线没有任何窗口或容器。X射线光谱仪的分辨率为