The little blue and red dot Rosetta stones
19 affiliations
- 1Cavendish Laboratory – Department of Physics, University of Cambridge
- 2Department of Physics, Astronomy Section, University of Trieste
- 3INAF – Osservatorio Astronomico di Trieste
- 4Kavli Institute for Cosmology, University of Cambridge
- 5Department of Physics and Astronomy, University College London
- 6Steward Observatory, University of Arizona
- 7Max-Planck-Institut für extraterrestrische Physik
- 8Dipartimento di Fisica e Astronomia “G. Galilei”, Università di Padova
- 9INAF-Osservatorio Astronomico di Padova
- 10Jeremiah Horrocks Institute, University of Central Lancashire
- 11Centro de Astrobiologia (CAB), CSIC-INTA
- 12IFPU – Institute for Fundamental Physics of the Universe
- 13INAF – Osservatorio Astrofisico di Arcetri
- 14Scuola Normale Superiore
- 15Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze
- 16Departamento de Astrofísica, Universidad de La Laguna
- 17Instituto de Astrofisica de Canarias
- 18Space Telescope Science Institute
- 19Department of Physics, University of Oxford, Denys Wilkinson Building
Abstract
The population of active galactic nuclei (AGNs) newly discovered by the James Webb Space Telescope (JWST) exhibits peculiar properties that distinguish it from both local type I AGNs and high-redshift quasars. Most of these sources are compact, appearing as ‘little dots’; among them, the sub-class (10−30% of the total) characterised by significantly red optical colours is known as ‘little red dots’ (LRDs). In this work, we introduce the analogous term ‘little blue dots’ (LBDs) to characterise the remaining (bluer) sources (70−90%). We present a comparative analysis of two bright prototypical representatives, which we refer to as the Rosetta stones of the two classes: GN-28074 at z=2.26 as the red Rosetta stone and GS-3073 at z=5.55 as the blue Rosetta stone. Both Rosetta stones exhibit non-Gaussian broad Balmer lines, better described by exponential or double-Gaussian profiles rather than single Gaussians, similarly to normal low-redshift type I AGNs, indicating that non-Gaussian wings are not unique to LRDs. They are both extremely X-ray weak, showing strong auroral λ 4363 emission, weak hot dust mid-IR emission, and no time variability. However, they do differ in terms of excitation diagnostics: the λ 4686 line is undetected in the red Rosetta, but strongly detected in the blue Rosetta in both narrow and broad components, with the latter being much broader than hydrogen Balmer lines. This supports BLR stratification and disfavours the cocoon electron-scattering scenario in LBDs. An additional difference is the presence of prominent Balmer absorption in the red Rosetta, which is indicative of extremely dense gas along the line of sight and also happens to be absent in the blue Rosetta. Taken together, these results suggest that LRDs and LBDs share the same central engine as standard type I AGNs, while differing in terms of the amount and geometry of dense gas surrounding the accretion disk and/or in their accretion properties.
Related
- Little Red and Blue Dots: AGN-excited narrow lines, Lyman-α emission, and resemblance to standard quasars
- Little red dots as obscured little blue dots: Relative abundances, luminosities, and black hole masses
- Little red dots as obscured little blue dots: relative abundances, luminosities, and black-hole masses
- Little red dots as obscured little blue dots: A super-Eddington unification model
- The nature of `little blue dots'
BibTeX
@article{brazzini2026little,
title = {{The little blue and red dot Rosetta stones}},
author = {M. Brazzini and Francesco D’Eugenio and R. Maiolino and J. Lyu and Christa DeCoursey and H. Übler and Xihan Ji and Ignas Juodžbalis and Jan Scholtz and Gareth C. Jones and Kevin Hainline and E. Dalla Bontà and Pablo G. Pérez‐González and Sophia Geris and Anishya Harshan and C. Feruglio and M. Bischetti and Giovanni Mazzolari and G. Rieke and S. Alberts and B. Trefoloni and Stefano Carniani and Eleonora Parlanti and A. Marconi and G. Risaliti and C. Ramos Almeida and P. Rinaldi and Michele Perna and Sandra Zamora and Isabella Lamperti and Giacomo Venturi and G. Cresci and E. Bertola and Andrew J. Bunker and Lucy R. Ivey},
journal = {Astronomy and Astrophysics},
year = {2026},
month = aug,
doi = {10.1051/0004-6361/202659249},
url = {https://doi.org/10.1051/0004-6361/202659249},
note = {CC BY},
}
RIS
TY - JOUR
TI - The little blue and red dot Rosetta stones
AU - M. Brazzini
AU - Francesco D’Eugenio
AU - R. Maiolino
AU - J. Lyu
AU - Christa DeCoursey
AU - H. Übler
AU - Xihan Ji
AU - Ignas Juodžbalis
AU - Jan Scholtz
AU - Gareth C. Jones
AU - Kevin Hainline
AU - E. Dalla Bontà
AU - Pablo G. Pérez‐González
AU - Sophia Geris
AU - Anishya Harshan
AU - C. Feruglio
AU - M. Bischetti
AU - Giovanni Mazzolari
AU - G. Rieke
AU - S. Alberts
AU - B. Trefoloni
AU - Stefano Carniani
AU - Eleonora Parlanti
AU - A. Marconi
AU - G. Risaliti
AU - C. Ramos Almeida
AU - P. Rinaldi
AU - Michele Perna
AU - Sandra Zamora
AU - Isabella Lamperti
AU - Giacomo Venturi
AU - G. Cresci
AU - E. Bertola
AU - Andrew J. Bunker
AU - Lucy R. Ivey
PY - 2026
DA - 2026/08/10
JO - Astronomy and Astrophysics
DO - 10.1051/0004-6361/202659249
UR - https://doi.org/10.1051/0004-6361/202659249
AB - The population of active galactic nuclei (AGNs) newly discovered by the James Webb Space Telescope (JWST) exhibits peculiar properties that distinguish it from both local type I AGNs and high-redshift quasars. Most of these sources are compact, appearing as ‘little dots’; among them, the sub-class (10−30% of the total) characterised by significantly red optical colours is known as ‘little red dots’ (LRDs). In this work, we introduce the analogous term ‘little blue dots’ (LBDs) to characterise the remaining (bluer) sources (70−90%). We present a comparative analysis of two bright prototypical representatives, which we refer to as the Rosetta stones of the two classes: GN-28074 at z=2.26 as the red Rosetta stone and GS-3073 at z=5.55 as the blue Rosetta stone. Both Rosetta stones exhibit non-Gaussian broad Balmer lines, better described by exponential or double-Gaussian profiles rather than single Gaussians, similarly to normal low-redshift type I AGNs, indicating that non-Gaussian wings are not unique to LRDs. They are both extremely X-ray weak, showing strong auroral λ 4363 emission, weak hot dust mid-IR emission, and no time variability. However, they do differ in terms of excitation diagnostics: the λ 4686 line is undetected in the red Rosetta, but strongly detected in the blue Rosetta in both narrow and broad components, with the latter being much broader than hydrogen Balmer lines. This supports BLR stratification and disfavours the cocoon electron-scattering scenario in LBDs. An additional difference is the presence of prominent Balmer absorption in the red Rosetta, which is indicative of extremely dense gas along the line of sight and also happens to be absent in the blue Rosetta. Taken together, these results suggest that LRDs and LBDs share the same central engine as standard type I AGNs, while differing in terms of the amount and geometry of dense gas surrounding the accretion disk and/or in their accretion properties.
SN - 0004-6361
SN - 1432-0746
ER -