{ "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.", "abstract_shown": true, "affiliations": [ "Cavendish Laboratory – Department of Physics, University of Cambridge", "Department of Physics, Astronomy Section, University of Trieste", "INAF – Osservatorio Astronomico di Trieste", "Kavli Institute for Cosmology, University of Cambridge", "Department of Physics and Astronomy, University College London", "Steward Observatory, University of Arizona", "Max-Planck-Institut für extraterrestrische Physik", "Dipartimento di Fisica e Astronomia “G. Galilei”, Università di Padova", "INAF-Osservatorio Astronomico di Padova", "Jeremiah Horrocks Institute, University of Central Lancashire", "Centro de Astrobiologia (CAB), CSIC-INTA", "IFPU – Institute for Fundamental Physics of the Universe", "INAF – Osservatorio Astrofisico di Arcetri", "Scuola Normale Superiore", "Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze", "Departamento de Astrofísica, Universidad de La Laguna", "Instituto de Astrofisica de Canarias", "Space Telescope Science Institute", "Department of Physics, University of Oxford, Denys Wilkinson Building" ], "article_type": null, "arxiv": null, "author_total": 35, "authors": [ { "affs": [ 0, 1, 2, 3 ], "name": "M. Brazzini", "orcid": "0009-0009-6418-7154" }, { "affs": [ 0, 3 ], "name": "Francesco D’Eugenio", "orcid": "0000-0003-2388-8172" }, { "affs": [ 0, 4, 3 ], "name": "R. Maiolino", "orcid": "0000-0002-4985-3819" }, { "affs": [ 5 ], "name": "J. Lyu" }, { "affs": [ 5 ], "name": "Christa DeCoursey", "orcid": "0000-0002-4781-9078" }, { "affs": [ 6 ], "name": "H. Übler", "orcid": "0000-0003-4891-0794" }, { "affs": [ 0, 3 ], "name": "Xihan Ji", "orcid": "0000-0002-1660-9502" }, { "affs": [ 0, 3 ], "name": "Ignas Juodžbalis", "orcid": "0009-0003-7423-8660" }, { "affs": [ 0, 3 ], "name": "Jan Scholtz", "orcid": "0000-0001-6010-6809" }, { "affs": [ 0, 3 ], "name": "Gareth C. Jones", "orcid": "0000-0002-0267-9024" }, { "affs": [ 5 ], "name": "Kevin Hainline", "orcid": "0000-0003-4565-8239" }, { "affs": [ 7, 8, 9 ], "name": "E. Dalla Bontà", "orcid": "0000-0001-9931-8681" }, { "affs": [ 10 ], "name": "Pablo G. Pérez‐González", "orcid": "0000-0003-4528-5639" }, { "affs": [ 0, 3 ], "name": "Sophia Geris", "orcid": "0000-0003-2709-2913" }, { "affs": [ 0, 3 ], "name": "Anishya Harshan", "orcid": "0000-0001-9414-6382" }, { "affs": [ 11, 2 ], "name": "C. Feruglio", "orcid": "0000-0002-4227-6035" }, { "affs": [ 1, 2 ], "name": "M. Bischetti", "orcid": "0000-0002-4314-021X" }, { "affs": [ 6 ], "name": "Giovanni Mazzolari", "orcid": "0009-0005-7383-6655" }, { "affs": [ 5 ], "name": "G. Rieke" }, { "affs": [ 5 ], "name": "S. Alberts" }, { "affs": [ 12, 13 ], "name": "B. Trefoloni", "orcid": "0009-0007-3295-8669" }, { "affs": [ 13 ], "name": "Stefano Carniani", "orcid": "0000-0002-6719-380X" }, { "affs": [ 13 ], "name": "Eleonora Parlanti", "orcid": "0000-0002-7392-7814" }, { "affs": [ 14, 12 ], "name": "A. Marconi", "orcid": "0000-0002-9889-4238" }, { "affs": [ 14, 12 ], "name": "G. Risaliti", "orcid": "0000-0002-3556-977X" }, { "affs": [ 15, 16 ], "name": "C. Ramos Almeida", "orcid": "0000-0001-8353-649X" }, { "affs": [ 17 ], "name": "P. Rinaldi", "orcid": "0000-0002-5104-8245" }, { "affs": [ 10 ], "name": "Michele Perna", "orcid": "0000-0002-0362-5941" }, { "affs": [ 13 ], "name": "Sandra Zamora", "orcid": "0000-0003-4546-897X" }, { "affs": [ 10, 14, 12 ], "name": "Isabella Lamperti", "orcid": "0000-0003-3336-5498" }, { "affs": [ 13 ], "name": "Giacomo Venturi", "orcid": "0000-0001-8349-3055" }, { "affs": [ 12 ], "name": "G. Cresci", "orcid": "0000-0002-5281-1417" }, { "affs": [ 12 ], "name": "E. Bertola", "orcid": "0000-0001-5487-2830" }, { "affs": [ 18 ], "name": "Andrew J. Bunker", "orcid": "0000-0002-8651-9879" }, { "affs": [ 0, 3 ], "name": "Lucy R. Ivey", "orcid": "0009-0002-5105-1222" } ], "bibtex": "https://research.draconitic.com/paper/7hdn773r4s409.bib", "cited_by": 69, "doi": "10.1051/0004-6361/202659249", "fulltext_url": null, "id": "7hdn773r4s409", "issns": [ "0004-6361", "1432-0746" ], "landing_url": "https://doi.org/10.1051/0004-6361/202659249", "language": "en", "licence": "CC-BY", "licence_label": "CC BY", "licence_source": "journal", "licence_url": "https://creativecommons.org/licenses/by/4.0/", "metadata_licence": null, "native_subjects": [ [ "openalex", "3103|Galaxies: Formation, Evolution, Phenomena" ] ], "openalex": "W7202138113", "pdf_url": null, "pmcid": null, "pmid": null, "published": "2026-08-10", "publisher": "EDP Sciences", "ris": "https://research.draconitic.com/paper/7hdn773r4s409.ris", "sources": [ { "first_seen": "2026-11-07T13:20:44Z", "native_id": "W7202138113", "source": "openalex", "url": "https://doi.org/10.1051/0004-6361/202659249" } ], "subjects": [ { "field": "astronomy", "origin": "openalex:3103|Galaxies: Formation, Evolution, Phenomena", "subfield": "galaxies" } ], "title": "The little blue and red dot Rosetta stones", "title_text": "The little blue and red dot Rosetta stones", "type": "peer-reviewed", "updated_at": "2026-11-09T13:21:01Z", "url": "https://research.draconitic.com/paper/7hdn773r4s409", "venue": "Astronomy and Astrophysics", "versions": [] }