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| Format: | Preprint |
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2025
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| Online Access: | https://arxiv.org/abs/2512.15853 |
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| author | Barro, Guillermo Perez-Gonzalez, Pablo G. Kocevski, Dale Trump, Jonathan R. Dickinson, Mark Haro, Pablo Arrabal Brooks, Madisyn Donnan, Callum T. Dunlop, James S. Finkelstein, Steven L. Franco, Maximilien Gandolfi, Giovanni Giavalisco, Mauro Grogin, Norman A. Hirschmann, Michaela Kartaltepe, Jeyhan S. Koekemoer, Anton M. Larson, Rebecca L. Leung, Gene C. K. Lucas, Ray A. McGrath, Elizabeth J. Papovich, Casey Perez-Diaz, Borja Somerville, Rachel S. Taylor, Elizabeth Taylor, Anthony J. Tripodi, Roberta Yung, L. Y. Aaron Wang, Xin |
| author_facet | Barro, Guillermo Perez-Gonzalez, Pablo G. Kocevski, Dale Trump, Jonathan R. Dickinson, Mark Haro, Pablo Arrabal Brooks, Madisyn Donnan, Callum T. Dunlop, James S. Finkelstein, Steven L. Franco, Maximilien Gandolfi, Giovanni Giavalisco, Mauro Grogin, Norman A. Hirschmann, Michaela Kartaltepe, Jeyhan S. Koekemoer, Anton M. Larson, Rebecca L. Leung, Gene C. K. Lucas, Ray A. McGrath, Elizabeth J. Papovich, Casey Perez-Diaz, Borja Somerville, Rachel S. Taylor, Elizabeth Taylor, Anthony J. Tripodi, Roberta Yung, L. Y. Aaron Wang, Xin |
| contents | One of JWST's most unexpected discoveries is the emergence of "Little Red Dots'' (LRDs): compact sources at $z \gtrsim 3$ with blue rest-frame UV continua, red optical slopes, and broad Balmer emission lines that challenge standard models and suggest a population of 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-S/N spectra, enabling a population-wide analysis of their UV-optical continuum and emission lines. We find clear correlations between rest-frame color ([0.3-0.9\,$μ$m]) and slopes: bluer LRDs have blue UV slopes ($β_{ν,\mathrm{UV}} \sim 0.3$) and red optical slopes, while redder LRDs exhibit redder UV slopes ($β_{ν,\mathrm{UV}} \sim 1.1$). The continuum shape shows a similar trend: redder LRDs display prominent Balmer breaks and curvature, while bluer LRDs follow power-law-like optical SEDs. From literature compilations, $\sim$60% of known broad-line AGNs satisfy our LRD criteria, and up to 90% of LRDs show broad Balmer lines. Emission-line diagnostics reveal a shift from high H$_α$/H$_β$ and low [OIII]$\lambda5007$/H$_β$ 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 host-to-BH luminosity ratio. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2512_15853 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | From "The Cliff" to "Virgil": Mapping the Spectral Diversity of Little Red Dots with JWST/NIRSpec Barro, Guillermo Perez-Gonzalez, Pablo G. Kocevski, Dale Trump, Jonathan R. Dickinson, Mark Haro, Pablo Arrabal Brooks, Madisyn Donnan, Callum T. Dunlop, James S. Finkelstein, Steven L. Franco, Maximilien Gandolfi, Giovanni Giavalisco, Mauro Grogin, Norman A. Hirschmann, Michaela Kartaltepe, Jeyhan S. Koekemoer, Anton M. Larson, Rebecca L. Leung, Gene C. K. Lucas, Ray A. McGrath, Elizabeth J. Papovich, Casey Perez-Diaz, Borja Somerville, Rachel S. Taylor, Elizabeth Taylor, Anthony J. Tripodi, Roberta Yung, L. Y. Aaron Wang, Xin Astrophysics of Galaxies One of JWST's most unexpected discoveries is the emergence of "Little Red Dots'' (LRDs): compact sources at $z \gtrsim 3$ with blue rest-frame UV continua, red optical slopes, and broad Balmer emission lines that challenge standard models and suggest a population of 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-S/N spectra, enabling a population-wide analysis of their UV-optical continuum and emission lines. We find clear correlations between rest-frame color ([0.3-0.9\,$μ$m]) and slopes: bluer LRDs have blue UV slopes ($β_{ν,\mathrm{UV}} \sim 0.3$) and red optical slopes, while redder LRDs exhibit redder UV slopes ($β_{ν,\mathrm{UV}} \sim 1.1$). The continuum shape shows a similar trend: redder LRDs display prominent Balmer breaks and curvature, while bluer LRDs follow power-law-like optical SEDs. From literature compilations, $\sim$60% of known broad-line AGNs satisfy our LRD criteria, and up to 90% of LRDs show broad Balmer lines. Emission-line diagnostics reveal a shift from high H$_α$/H$_β$ and low [OIII]$\lambda5007$/H$_β$ 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 host-to-BH luminosity ratio. |
| title | From "The Cliff" to "Virgil": Mapping the Spectral Diversity of Little Red Dots with JWST/NIRSpec |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2512.15853 |