超越方位：小红点与小蓝点之间不同物理机制的证据
Beyond orientation: Evidence for distinct physical regimes among Little Red Dots and Little Blue Dots
AI总结：
本研究利用DAWN JWST存档光谱样本，发现LRDs与LBDs并非仅因观测方位不同，而是存在不同物理机制，其Hα光度、轮廓、巴耳末减缩等特性差异支持气体茧模型的转变机制。
AI中文摘要：
小红点（LRDs）和小蓝点（LBDs）可能代表同一批致密活动星系核（AGN），只是观测视线方向不同。我们利用来自DAWN JWST存档的光谱样本对该假设进行检验，该样本基于Hα等效宽度、紫外连续谱斜率和致密性的共同标准选取。我们利用光学连续谱斜率区分出89个LRDs和191个LBDs样本，其红移范围为1≤z≤7.5，并比较它们的连续谱特性、Hα发射和巴耳末减缩。与先前研究一致，我们发现LRDs的Hα轮廓系统上比LBDs更宽，中值半高全宽（FWHM）分别为2319⁺⁷¹₋₆⁴ km/s和1424⁺⁵⁶₋₄³ km/s。我们还证实LRDs表现出更大的巴耳末减缩，中值log₁₀(F_Hα/F_Hβ)=1.01±0.03，而LBDs为0.47±0.01。视线效应可能解释这两个结果。但最显著的是，我们发现LRDs的比例随Hα线光度强烈增加：LRDs的Hα光度约为LBDs的6倍。这一可靠发现很难通过与LBDs的方位统一来解释。尽管LRDs具有更高的线光度，其中值Hα等效宽度却略低于LBDs，这与LRDs中更多原始发射被重处理为静止帧光学连续谱一致。这些结果，加上LRDs中系统上更低的[O III]/Hβ比率以及Hα等效宽度随光学斜率变红而下降，不利于LRDs与LBDs之间基于简单方位的关联，反而更符合气体茧模型的预测，其中气体柱密度的增加解释了从LBDs到LRDs的明显转变。
英文摘要：
Little Red Dots (LRDs) and Little Blue Dots (LBDs) may represent the same population of compact active galactic nuclei (AGN) observed along different lines of sight. We test this scenario using a spectroscopic sample from the DAWN {\it JWST} Archive, selected based on common criteria for H$α$ equivalent width, UV continuum slope, and compactness. We use the optical continuum slope to distinguish between samples of 89 LRDs and 191 LBDs spanning $1 \lesssim z \lesssim 7.5$, and compare their continuum properties, H$α$ emission, and Balmer decrements. Consistent with previous studies, we find that LRDs exhibit broader H$α$ profiles than LBDs systematically (with median FWHM values of $2319^{+71}_{-64}$ and $1424^{+56}_{-43}~\mathrm{km\,s^{-1}}$, respectively). We also confirm that LRDs show larger Balmer decrements, with median $\log_{10}(F_{\rm Hα}/F_{\rm Hβ})=1.01\pm0.03$, compared with $0.47\pm0.01$ for LBDs. Line-of-sight effects could explain both results. However, most significantly, we find that the LRD fraction increases strongly with H$α$ line luminosity: LRDs are approximately six times more luminous in H$α$ than LBDs. This robust finding is much harder to explain through unification with LBDs by orientation. Despite their higher line luminosities, LRDs have a moderately lower median H$α$ equivalent width than LBDs, consistent with more of the raw emission being reprocessed into the rest-frame optical continuum in LRDs. These results, coupled with the systematically lower [O III]/H$β$ ratios found in LRDs and the decline of H$α$ equivalent width towards the reddest optical slopes, disfavour a simple orientation-based link between LRDs and LBDs, and are instead more consistent with the predictions of gas-cocoon models in which increasing gas column density explains the apparent transition from LBDs to LRDs.
