摘要
One of JWST's most unexpected discoveries is the emergence of "Little Red Dots" (LRDs), compact sources at z greater than or similar to 3 with blue rest-frame UV continua, red optical slopes, and broad Balmer emission lines that challenge standard models and suggest early, unusual active galactic nuclei (AGNs). Using a comprehensive photometric selection and public NIRSpec/PRISM spectroscopy across six JWST deep fields, we identify a large sample of 118 LRDs with high-signal-to-noise-ratio spectra, enabling a population-wide analysis of their UV-optical continuum and lines. We find clear correlations between rest-frame UV-optical color ([0.3-0.9 mu m]) and slopes; bluer LRDs have blue UV slopes (beta nu,UV similar to 0.3) and red optical slopes, while redder LRDs exhibit redder UV slopes (beta nu,UV similar to 1.1). The continuum shape shows a similar trend; redder LRDs display prominent Balmer breaks and curvature, while bluer LRDs follow power-law-like optical spectral energy distributions. From literature compilations, similar to 60% of known broad-line AGNs satisfy our LRD criteria, and up to 90% of LRDs show broad Balmer lines. Emission line diagnostics reveal a shift from high H alpha/H beta and low [O iii]lambda 5007/H beta in redder LRDs to the opposite in bluer ones, along with stronger narrow-line equivalent widths, suggesting a transition from AGN- to host-dominated emission. We fit the spectra with a two-component model combining a gas-enshrouded black hole (BH) and a galaxy host. Redder LRDs require higher-luminosity, unreddened BHs and modestly reddened hosts; bluer LRDs require lower-luminosity, reddened BHs and dust-free galaxies. This framework reproduces the diversity in colors and spectral shape by varying BH luminosity, obscuration, and BH-to-host luminosity ratio.