AI 中文总结
该研究利用JWST光谱数据等，分析0<z<8星系的低电离电子密度演化，发现z~4后电子密度不再随红移单调增长，提出气体团块演化模型解释相关变化。
AI 中文摘要
我们利用JWST NIRCam/光栅和NIRSpec/MSA光谱，通过[O II]λλ3727,3730和[S II]λλ6718,6733双线，研究了0<z<8范围内星系星际介质中的低电离电子密度。结合文献中0<z<6的辅助密度样本，我们组装了三个样本：共703个星系，红移范围为3.7<z<7.8，平均红移<z>约为5.6；亮度完整的NIRCam/光栅项目CONGRESS和FRESCO的691个星系，平均红移分别约为4.3和5.3；以及来自GO 1871和GLASS项目的12个具有高分辨率NIRSpec/MSA光谱的星系。我们发现CONGRESS样本的中值电子密度nₑ[S II]=463⁺²⁸¹₋₂₀³ cm⁻³，FRESCO样本的nₑ[S II]=301⁺³⁸⁸₋₂₀⁶ cm⁻³，NIRSpec/MSA样本的nₑ[O II]=202⁺¹⁴⁵₋₁₀² cm⁻³。中值低电离nₑ从z=0到z=4逐渐增加，与以往研究及JWST观测结果一致，但在z~4之后，中值nₑ不再随红移单调增长。我们发现O₃₂（电离参数的示踪剂）与nₑ呈正相关但较浅，同时确认O₃₂与z呈正相关。我们认为这些趋势可能源于星际介质（ISM）气体密度和电离结构的演化，并提出一个气体团块随红移演化的简化模型来解释观测到的密度和电离变化。
英文摘要
We investigate the low-ionization electron density in the interstellar medium of galaxies across $0$$<$$z$$<$$8$, derived with the [O II]$λ\lambda3727,3730$ and [S II]$λ\lambda6718,6733$ doublets, using both deep JWST NIRCam/grism and NIRSpec/MSA spectroscopy. Along with ancillary density samples from the literature at $0$$<$$z$$<$$6$, we assemble three samples containing a total of 703 galaxies spanning $3.7$$<$$z$$<$$7.8$ at $\langle z\rangle\sim5.6$; 691 galaxies in the luminosity-complete NIRCam/grism programs CONGRESS and FRESCO at $\langle z\rangle \sim4.3$ and $\langle z\rangle\sim5.3$, respectively, and 12 galaxies with high-resolution NIRSpec/MSA spectra from the GO 1871 and GLASS programs. We find median electron densities of $n_{\rm{e}}$[S II]$=$$463^{+281}_{-203}~{\rm{cm}}^{-3}$ for CONGRESS, $n_{\rm{e}}$[S II]$=$$301^{+388}_{-206}~{\rm{cm}}^{-3}$ for FRESCO, and $n_{\rm{e}}$[O II]$=$$202^{+145}_{-102}~{\rm{cm}}^{-3}$ for the NIRSpec/MSA sample. The median low-ionization $n_{\rm{e}}$ increases from $z= 0$ to $z=4$, in agreement with previous studies and those using JWST observations. However, beyond $z\sim4$ median $n_{\rm{e}}$ begins to deviate from a monotonically increasing evolution with $z$. We find a positive, but shallow, correlation between O$_{32}$ (a proxy for the ionization parameter) and $n_{\rm{e}}$, while also confirming a positive correlation between O$_{32}$ and $z$. We suggest that these trends are possibly due to an evolving ISM gas density and ionization structure, and propose a toy model where the gas clumping evolves with $z$ to explain the observed density and ionization variations.
