AI 中文总结
本研究观测z~7-8处两个小红点星系，发现其宽线气体密度远高于低红移类星体，氮增强且需额外电离源，支持其气体包层高度分层的吸积盘+恒星电离模型。
AI 中文摘要
我们给出了z=6.68和z=8.35处两个小红点星系（Little Red Dots, LRDs）的近红外光谱仪（NIRSpec）G140M和G395M深场光谱观测结果。两个LRDs均呈现宽的巴尔末线及[O III] λ4364发射线，宽[O III] λ4364线的半高全宽（FWHM）约为1000 km/s，约为Hβ线的1/3。假设气体温度T~15000-25000 K，宽线的[O III] λ4364/[O III] λ5008比值得出气体密度log n/cm^-3为6.3至7.9，比低红移类星体宽线区的气体密度高3-10倍。若宽线反映位力运动，则这表明LRDs中心引擎附近存在金属增强的气体云，距离约1-10 pc。两个LRDs还呈现窄的[C III] λ1907 + C III] λ1909及O III] λλ1661,1666发射线，C III]比值得出窄线区气体密度log n/cm^-3为4.2-5.2，与其他恒星形成星系的密度相似。发射线的等值宽度EW(O III])、EW(C III])达到或超过恒星族群预期的极限，可能需要额外的电离源。两个LRDs的[O III] λ4364/Hγ比值支持电离来自吸积盘，可能结合恒星的贡献。基于探测到的N III] λ1746或N IV] λ1486，两个LRDs均呈现氮增强，这可能意味着近期存在快速恒星形成。这些结果支持以下情景：LRDs的气体包层高度分层，具有高密气体云、非1的覆盖因子及复杂几何结构，使得LRDs吸积盘的电离辐射与恒星形成区的电离辐射共同产生了星云发射特征。
英文摘要
We present deep, NIRSpec G140M and G395M spectroscopy of Little Red Dots (LRDs) at z = 6.68 and z = 8.35. Both LRDs show broad Balmer and [O III] $λ$4364 emission. The broad [O III] $λ$4364 lines have FWHM ~1000 km/s, about 1/3 that of the H$β$ lines. Assuming gas temperatures T ~ 15,000 - 25,000 K, the [O III] $λ$4364/[O III] $λ$5008 ratios of the broad lines yield high gas densities, log n/cm^-3 = 6.3 to 7.9, 3-10$\times$ higher than those in broad-line regions of low-redshift quasars. If the broad-lines trace virial motions, it is evidence for metal-enhanced gas clouds, ~1-10~pc from the LRD engine. Both LRDs show narrow [C III] $λ$1907 + C III] $λ$1909, and O III] $λλ$1661,1666. The C III] ratios yield narrow-line gas densities, log n/cm^-3 = 4.2-5.2, similar to those in other star-forming galaxies. The line equivalent widths, EW(O III]), EW(C III]), are at, or exceed, limits expected for stellar populations, likely requiring an additional ionizing source. The LRDs also have [O III] $λ$4364/H$γ$ ratios that favor ionization from an accretion disk, possibly combined with stars. Both LRDs show nitrogen enhancement based on detections of N III] $λ$1746 or N IV] $λ$1486, which may imply rapid, recent star-formation. These results favor a scenario where the LRD gas envelopes are highly stratified, having high-density clouds with a non-unity covering factors and a complex geometry, such that ionizing radiation from the LRD accretion disk, combined with that from star-forming regions, produce the nebular emission features.
CommentsSubmitted to ApJ; 24 pages, 14 figures. Comments welcome
