From "The Cliff" to "Virgil": Mapping the Spectral Diversity of Little Red Dots with JWST/NIRSpec

One of JWST’s most unexpected discoveries is the emergence of ``Little Red Dots’ (LRDs), compact sources at z {\ensuremath{\gtrsim}} 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{\ensuremath{-}}0.9 {\ensuremath{\mu}}m]) and slopes; bluer LRDs have blue UV slopes ({\ensuremath{\beta}}$_{{\ensuremath{\nu}},UV}$ {\ensuremath{\sim}} 0.3) and red optical slopes, while redder LRDs exhibit redder UV slopes ({\ensuremath{\beta}}$_{{\ensuremath{\nu}},UV}$ {\ensuremath{\sim}} 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, {\ensuremath{\sim}}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{\ensuremath{\alpha}}/H{\ensuremath{\beta}} and low [O III]{\ensuremath{\lambda}}5007/H{\ensuremath{\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.