AI 中文总结
本研究使用UCLCHEM化学代码，发现HCO⁺在特定温度、密度和宇宙射线电离率组合下可出现极端丰度，且丰度受化学网络影响，UMIST22会导致其丰度显著高于UMIST12。
AI 中文摘要
背景：HCO⁺在银河系和河外星系环境中被广泛观测到，其丰度通常为10⁻⁹-10⁻⁸。然而，近期的模型研究表明，在暴露于升高的宇宙射线电离率以及强热或机械处理的环境中，其丰度可能增加数个数量级。目标：为解释这些预测，需要了解产生HCO⁺极端丰度的物理条件，以及驱动这些丰度增强的化学路径。方法：使用气体-尘埃化学代码UCLCHEM，在升高的宇宙射线电离率（ζ ≥ 10⁻¹⁵ s⁻¹）下，对致密分子、原恒星和受激气体中的HCO⁺化学进行建模。结果：导致X(HCO⁺) ≳ 10⁻⁴的HCO⁺极端增强仅发生在温度、密度和宇宙射线电离率的特定组合下，主要出现在原恒星和受激气体中。增加密度通常会抑制HCO⁺的峰值丰度，需要更高的电离率才能产生相当的增强。更重要的是，这种极端增强似乎高度依赖所使用的化学网络（本研究中为UMIST12与UMIST22，后者会导致极端丰度）。网络之间的这些差异源于HCO⁺的一条破坏路径被移除：C + HCO⁺ → CO + CH⁺，并会传播到包括N₂H⁺、H₂O和H₃O⁺在内的其他多种物种。
英文摘要
Context. HCO$^+$ is widely observed in both Galactic and extragalactic environments and typically exhibits abundances of $10^{-9}-10^{-8}$. However, recent modeling studies suggest that in environments exposed to elevated cosmic-ray ionization rates and strong thermal or mechanical processing its abundance may increase by several orders of magnitude. Aims. To interpret these predictions, we need to understand the physical conditions that produce extreme HCO$^+$ abundances and the chemical pathways that drive these enhancements. Methods. We used UCLCHEM, a gas-grain chemical code, to model the chemistry of HCO$^+$ in dense molecular, protostellar, and shocked gas under elevated cosmic-ray ionization rates ($ζ\ge 10^{-15}\,\mathrm{s^{-1}}$). Results. Extreme HCO$^+$ enhancements leading to $X$(HCO$^+$) $\gtrsim 10^{-4}$ occur only under specific combinations of temperature, density, and cosmic-ray ionization rate, primarily in protostellar and shocked gas. Increasing density generally suppresses the peak HCO$^+$ abundance, requiring higher ionization rates to produce comparable enhancements. More importantly, the extreme enhancements seem to be very dependent on the chemical network used (in our case UMIST12 versus UMIST22, with the latter leading to extreme abundances). These differences among networks arise from the removal of the destruction pathway of HCO$^+$: C + HCO$^+$ $\rightarrow$ CO + CH$^+$, and propagate to several other species including N$_2$H$^+$, H$_2$O, and H$_3$O$^{+}$.
CommentsAccepted for publication in A&A. 13 pages, 16 figures
