摘要
We compile JWST/NIRSpec prism and MIRI data for 249 Little Red Dots (LRDs) at 2.3<z<9.3, forming a representative spectroscopic subset of NIRCam-selected LRDs. We derive a median stacked spectrum covering rest-frame 0.09-1.2μ m, with MIRI photometry extending the spectral energy distribution to 4μ m. Four additional stacks for subsamples defined by optical-to-UV luminosity ratios show that LRDs form a heterogeneous population spanning diverse continuum slopes and line properties. Assuming LRDs host super-massive black holes (BHs) surrounded by dense gas clouds, and stars accompany this core, we infer masses ofM_(BH)∼10^(6.0-6.5)M _(⊙)andM_(★)∼10^(8.3)M _(⊙) , corresponding to BH-to-stellar mass ratios of 1-2%. The stacks show ubiquitous UV and optical FeII emission, indicating a direct view of the broad-line region and high (but sub-Eddington) accretion ( λ_(Edd)=0.6±0.2 ). We find a significant stellar contribution in the far-UV, reaching∼80 % in the bluest systems. Possible Wolf-Rayet features (HeII λ 4687, nitrogen lines) are identified, tracing a young (3-7 Myr) compact starburst event. We also detect strong Balmer breaks and atypical Balmer, Paschen, [OIII], and optical and near-infrared HeI line ratios, and an absorption at∼4550Angstrom (probably linked to FeII), all consistent with radiative-transfer effects in high-density gas with warm temperatures (4000-7000 K). We find a diversity of LRD flavors modulated by the luminosity ratio between between a short ( ≲20Myr) and intense phase of BH activity, the most extreme stage lasting∼3-7Myr, characterized by near-Eddington-limit radiation, and a nuclear and compact starburst dominated by massive stars (even super-massive,\mathrm{M}{_(\mathrm{SMS}{∼}{1})}{0}⁵M _(⊙) ), all embedded in dense gas with modest dust content producing a variety of optical depths.