بنية "النقاط الحمراء الصغيرة": تشريح أنوية المجرات في الكون المبكر ✛ ✦

الملخص الأصلي

كما كتبه المؤلفون، بالإنجليزية arXiv:2606.04711v1

We present a spectroscopic analysis of 14 little red dots (LRDs) at redshifts $$2.2 < z < 6.7$$ using NIRSpec/MSA prism and medium-resolution grating observations, aiming to constrain the nuclear gas structure through Balmer emission-line profiles, absorption features, relative line intensities, and continuum properties. We simultaneously decompose the broad, narrow, and absorption components of $${\rm H \alpha}$$, $${\rm H \beta}$$, and $${\rm H \gamma}$$, and measure both integrated line ratios and velocity-resolved Balmer decrements. The narrow-line Balmer decrements are broadly consistent with Case~B recombination modified by mild dust attenuation, while the broad-line decrements are elevated to levels consistent with photoionization models of high-density gas at $$n_{\rm H} \gtrsim 10^9\ {\rm cm^{-3}}$$. Velocity-resolved Balmer decrements in five sources with highest signal-to-noise ratio are centrally peaked. Assuming virialized broad-line region dynamics, our model can reproduce the Balmer decrement profiles in three sources using a radial density profile with a power-law index $$\beta<2$$. The Balmer absorption lines detected in six sources yield absorber covering factors exceeding $$50\%$$. Sources with blueshifted absorption lines tend to have elevated narrow-line Balmer decrement, suggesting a connection between dust content and the presence of outflow. Comparing the incident luminosity inferred from broad and narrow $${\rm H \alpha}$$ emission with the continuum suggests that both the UV and optical continuum and the line emission are linked by photoionization. We propose that the distinctive spectral and continuum properties of LRDs can be explained via a viewing angle-dependent nuclear structure in which an optically thick, clumpy gaseous torus surrounds the central accretion disk, with broad-line clouds and absorbers distributed along the less-obscured polar directions.