AI 中文总结
该研究通过JWST光谱统计z≈2.5-7.2的LRDs中巴尔末线吸收特性，发现其发生率约为35%，显著高于低红移1型AGNs，且多数吸收体蓝移，多数高密度吸收体受引力束缚，向外运动的吸收体密度降低。
AI 中文摘要
我们利用来自DAWN JWST档案的存档JWST/NIRSpec光谱及互补的NIRSpec/IFU观测，呈现了红移z≈2.5-7.2的低红移星系团（LRDs）中Hα和Hβ线吸收的统计特性。在通过中或高分辨率光栅获得的40个具有宽Hα和[O III]的LRDs中，14个天体表现出Hα吸收。我们发现巴尔末线吸收的发生率约为35%（=14/40），显著高于SDSS低红移1型AGNs中的发生率（约0.04%），表明巴尔末线吸收在LRDs中的发生频率约为1型AGNs的850倍。我们将我们的14个探测结果与文献中另外32个LRD巴尔末吸收体相结合，形成了共46个吸收体的统计样本。它们的速度范围为Δv_abs(Hα)≈-430至+140 km·s⁻¹，明显窄于SDSS 1型AGNs中巴尔末吸收的-800至+1600 km·s⁻¹范围，我们的模拟证实这种速度差异过大，无法用探测不完整性来解释。LRDs中吸收体的较低绝对速度可能部分反映了其特征宽线区（BLR）半径处更浅的引力势。我们还发现，46个吸收体中的38个（83%）为蓝移，仅有8个为红移，表明大多数巴尔末吸收体在向外运动。一个具有辐射压的分析模型表明，大多数N_H≥10²⁴ cm⁻²的吸收体仍受引力束缚。红移（即向内下落）吸收体数量较少可能表明向外运动的吸收体密度降低：一些返回宽线区，而另一些则经历更强的辐射加速并逃逸。
英文摘要
We present the statistical properties of H$α$ and H$β$ line absorption in little red dots (LRDs) at $z\simeq2.5$--7.2 using archival JWST/NIRSpec spectra from the DAWN JWST Archive and complementary NIRSpec/IFU observations. Among 40 LRDs with broad H$α$ and [O~{\sc iii}] obtained with medium- or high-resolution gratings, 14 objects exhibit H$α$ absorption. We find that the incidence of Balmer line absorption is $\sim35$\% ($=14/40$), significantly higher than that in SDSS low-$z$ type 1 AGNs ($\sim0.04$\%), demonstrating that Balmer line absorption occurs approximately 850 times more frequently in LRDs than in type 1 AGNs. We combine our 14 detections with 32 additional LRD Balmer absorbers from the literature, yielding a census of 46 absorbers. Their velocities span $Δv_\mathrm{abs}(\mathrm{Hα})\sim-430$ to $+140\ {\rm km\,s^{-1}}$, markedly narrower than the $-800$ to $+1600\ {\rm km\,s^{-1}}$ range of Balmer absorption in SDSS type~1 AGNs, for which our simulations confirm that the velocity difference is too large to be explained by detection incompleteness. The lower absolute absorber velocities in LRDs may partly reflect the shallower gravitational potential at their characteristic BLR radii. We also find that 38 of the 46 absorbers (83\%) are blueshifted, with only eight redshifted, indicating that most of Balmer absorbers are moving outward. An analytic model with radiation pressure suggests that most absorbers with $N_{\rm H}\gtrsim10^{24}\ {\rm cm^{-2}}$ remains gravitationally bound. The smaller number of redshifted (i.e., infalling) absorbers may indicate that outbound absorbers lose density: some return to the BLR, whereas others undergo stronger radiative acceleration and escape.
Comments22 pages, 11 figures, 2 tables. Submitted to ApJ
