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arXiv 2503.23971astro-ph.CO
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黑暗时代首批分子对宇宙微波背景谱的畸变

Distortion of the CMB spectrum by the first molecules of the Dark Ages

Yurii Kulinich, Bohdan Novosyadlyj

AI总结:

本文通过166个化学反应和振转能级跃迁动力学,计算了黑暗时代首批分子H$_2$、HD和HeH$^+$对CMB谱的吸收畸变,并给出各分子的频率、强度和红移范围。

摘要:

宇宙黎明时期第一批恒星和星系的形成之前,黑暗时代已经发生了一系列原初化学反应,生成了第一批分子,主要是H$_2$、HD和HeH$^+$,这些分子对第一批恒星的出现至关重要。这些分子吸收并散射了宇宙微波背景(CMB)量子,从而使CMB谱发生畸变。本文估计了在标准$Λ$CDM宇宙学中,H$_2$、HD和HeH$^+$分子振转能级之间的束缚-束缚跃迁对CMB谱畸变的贡献。我们用包含20种反应物和166个化学反应的系统描述了第一批分子的形成动力学。通过求解微分方程组来描述H$_2$、HD和HeH$^+$分子振转能级之间的自发跃迁和碰撞跃迁过程。利用振转能级的布居数以及这些能级之间跃迁谱线的气体光学厚度,估计了第一批分子在宇宙微波背景上产生的微分亮度。研究表明,在标准$Λ$CDM宇宙学中,来自第一批分子的信号在CMB谱中表现为吸收轮廓,并且起源于黑暗时代。H$_2$表现出多个峰,在50-120 GHz之间峰值约为$10^{-3}$ Jy/sr,吸收主要来自$300>z>200$。HD具有双峰,在40-70 GHz之间达到约$10^{-5}$ Jy/sr,吸收来自$300>z>30$。HeH$^+$没有明显谱线特征,在200-800 GHz之间峰值约为$10^{-7}$ Jy/sr,主要从$100>z>4$吸收。

英文摘要:

The formation of first stars and galaxies at the Cosmic Dawn had been preceded by the chain of primordial chemistry reactions during Dark Ages which generated first molecules, mostly H$_2$, HD, and HeH$^+$, so crucial for first stars to emerge. These molecules absorbed and scattered CMB quanta this way distorting CMB spectrum. Estimate how much bound-bound transitions between the rovibrational levels of H$_2$, HD, and HeH$^+$ molecules contribute to the distortion of CMB spectrum in the standard $Λ$CDM cosmology. We describe the kinetics of the formation of the first molecules with system of 166 chemical reactions involving 20 reagents. The system of differential equations is solved to describe the processes of spontaneous and collisional transitions between rovibrational levels of H$_2$, HD, and HeH$^+$ molecules. The populations of rovibrational levels and optical thickness of the gas in transition lines between these levels were used to estimate the differential brightness produced by the first molecules on the cosmic microwave background. It is shown that the signal from the first molecules in the standard $Λ$CDM cosmology takes the form of an absorption profile in the CMB spectrum and originates from the Dark Ages. H$_2$ shows multiple peaks, peaking at $\sim 10^{-3}$ Jy/sr between 50-120 GHz, with absorption from $300>z>200$. HD has double peaks, reaching $\sim 10^{-5}$ Jy/sr between 40-70 GHz, with absorption from $300>z>30$. HeH$^+$ has no features, peaks at $\sim 10^{-7}$ Jy/sr between 200-800 GHz, and absorbs mainly from $100>z>4$.

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