小红点作为超爱丁顿喷泉流
Little Red Dots As Super-Eddington Fountain Flows
- Princeton University（普林斯顿大学）
- Tel Aviv University（特拉维夫大学）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本文提出小红点是由偏离视轴观测的超爱丁顿超大质量黑洞被慢速光子疲劳风包裹所致，通过辐射转移模拟重现了从蓝点到红LRD的光谱序列。
AI中文摘要：
小红点（LRDs）可能由以超过爱丁顿极限吸积的超大质量黑洞（SMBHs）提供能量。对LRDs的光谱观测通常显示出蓝移约$\sim100-300\\,{\rm km\\,s^{-1}}$的吸收槽，暗示存在慢速风。这令人费解：超爱丁顿盘驱动快得多的风，速度$\gtrsim10^3-10^4\\,{\rm km\\,s^{-1}}$。我们认为LRDs是偏离视轴观测的超爱丁顿超大质量黑洞，被覆盖大多数视线的慢速风所包裹；快速风则从两极附近逃逸。被束缚的光将内盘膨胀成准球形包层，从而发射慢速风。这种风可能是“光子疲劳”的，意味着光仅勉强使其解束缚。这种勉强未束缚的风导致喷泉流，其中部分气体逃逸，其余部分回落。我们用理想化的、球对称的“勉强未束缚”（$v\sim v_{\rm esc}$）和“光子疲劳”风对包层进行建模。我们将这些轮廓输入辐射转移代码Sirocco，研究风如何再处理来自吸积的$10^6\\,M_\odot$超大质量黑洞的光。我们将大部分风描述为“巴耳末茧”——一个康普顿厚区域，其中巴耳末连续谱光子（$h\nu >3.4\\,{\rm eV}$）而非莱曼连续谱光子（$h\nu > 13.6\\,{\rm eV}$）的损耗使气体保持电离。光谱覆盖了类LRD源的范围：较低外流率（$\sim2.5\\,M_\odot\\,{\rm yr}^{-1}$）的“小蓝点”；具有巴耳末跳变的V形LRD（$\sim5-10\\,M_\odot\\,{\rm yr}^{-1}$）；以及具有完整跳变的红色LRD（$\sim15\\,M_\odot\\,{\rm yr}^{-1}$）。我们的巴耳末线轮廓显示出在宽指数翼之上的P Cygni特征，与观测一致。由于莱曼$\alpha$俘获维持了我们的$n=2$氢布居，且电子散射增强了光学深度，因此跳变在比LTE模型中更低的风密度下成为可能。我们的论证也适用于超大质量恒星或准恒星的风。
英文摘要：
Little red dots (LRDs) may be powered by supermassive black holes (SMBHs) accreting above the Eddington limit. Spectroscopy of LRDs often shows absorption troughs blueshifted by $\sim100-300\,{\rm km\,s^{-1}}$, implying a slow wind. This is puzzling: super-Eddington disks drive much faster winds, $\gtrsim10^3-10^4\,{\rm km\,s^{-1}}$. We argue that LRDs are super-Eddington SMBHs viewed off-axis and engulfed in a slow wind that covers most sight-lines; the fast wind escapes near the poles. Trapped light puffs the inner disk into a quasi-spherical envelope that launches the slow wind. The wind may be ``photon-tired'', meaning the light only barely unbinds it. Such marginally unbound winds lead to fountain flows, where some gas escapes and the rest falls back. We model the envelope with idealized, spherically symmetric ``marginally unbound'' ($v\sim v_{\rm esc}$) and ``photon-tired'' winds. We feed these profiles into the radiative transfer code Sirocco to study how the wind reprocesses the light from an accreting $10^6\,M_\odot$ SMBH. We describe most of the wind as a ``Balmer cocoon'' -- a Compton-thick region in which depletion of Balmer continuum photons ($hν>3.4\,{\rm eV}$) rather than Lyman continuum photons ($hν> 13.6\,{\rm eV}$) keeps the gas ionized. The spectra span the range of LRD-like sources: ``little blue dots'' at lower outflow rates ($\sim2.5\,M_\odot\,{\rm yr}^{-1}$); V-shaped LRDs with a Balmer break ($\sim5-10\,M_\odot\,{\rm yr}^{-1}$); and red LRDs with full breaks ($\sim15\,M_\odot\,{\rm yr}^{-1}$). Our Balmer line profiles show P~Cygni features atop broad, exponential wings, as is observed. The break is possible at lower wind densities than in LTE models because Lyman~$α$ trapping sustains our $n=2$ hydrogen population and electron scattering enhances the optical depth. Our arguments are also applicable to winds from supermassive stars or quasi-stars.
