Do little red dots really form a distinct class of astronomical objects?
Fuente:
arXiv
Guardado en:
| Autores principales: | , , , , , , , , , , |
|---|---|
| Formato: | Preprint |
| Publicado: |
2026
|
| Materias: | |
| Acceso en línea: | |
| Etiquetas: |
Agregar Etiqueta
Sin Etiquetas, Sea el primero en etiquetar este registro!
|
| _version_ | 1866911628904103936 |
|---|---|
| author | Billand, Jean-Baptiste Elbaz, David Franco, Maximilien Gentile, Fabrizio Daddi, Emanuele Giavalisco, Mauro Kocevski, Dale D. Lewis, Joseph S. W. Magnelli, Benjamin Sangalli, Valentina Tarrasse, Maxime |
| author_facet | Billand, Jean-Baptiste Elbaz, David Franco, Maximilien Gentile, Fabrizio Daddi, Emanuele Giavalisco, Mauro Kocevski, Dale D. Lewis, Joseph S. W. Magnelli, Benjamin Sangalli, Valentina Tarrasse, Maxime |
| contents | JWST observations have identified a class of enigmatic sources known as "Little Red Dots" (LRDs). These have been interpreted as a distinct class of active galactic nuclei (AGN) and host galaxies, potentially involving "quasi-stars" or Black Hole stars (BH*). However, two questions remain: is there a clear discontinuity between LRDs and field galaxies, and do LRDs form a homogeneous population? In this work, we address these issues by introducing a continuous metric to evaluate the "LRDness" of galaxies. We measure their compactness ($δ_{compact}$), the sharpness of the V-shaped spectral energy distribution ($δ_{v-shape}$), and the strength of the broad Balmer line emission. We apply this approach to a sample of ~48,000 galaxies with photometric and ~5,000 with spectroscopic information, selected over ~750 arcmin^2. We find that V-shape prominence correlates strongly with morphology without a clear transition at common LRD selection thresholds: the fraction of compact galaxies rises continuously with V-shape intensity. Similarly, broad H$α$ strength increases with both V-shape sharpness and compactness. The [N II] deficit is not an exclusive feature of LRDs but a global property of compact, metal-poor galaxies. Only the 3% most extreme LRDs present a prominent Balmer break (>3) of potentially non-stellar origin. LRDs and non-LRDs follow similar trends in the evolution of the Balmer decrement with V-shape sharpness, suggesting a shared physical origin, likely dust attenuation. Estimated dust masses (~4-7 x 10^4 M_{sun}) and luminosities are low enough to account for their non-detection by ALMA. We conclude that most LRDs do not represent a separate class of objects, but rather the extreme tail of a continuous distribution of galaxies and broad H$α$ emitters, consistent with a classical broad line region and dust attenuation. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2604_11677 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Do little red dots really form a distinct class of astronomical objects? Billand, Jean-Baptiste Elbaz, David Franco, Maximilien Gentile, Fabrizio Daddi, Emanuele Giavalisco, Mauro Kocevski, Dale D. Lewis, Joseph S. W. Magnelli, Benjamin Sangalli, Valentina Tarrasse, Maxime Astrophysics of Galaxies JWST observations have identified a class of enigmatic sources known as "Little Red Dots" (LRDs). These have been interpreted as a distinct class of active galactic nuclei (AGN) and host galaxies, potentially involving "quasi-stars" or Black Hole stars (BH*). However, two questions remain: is there a clear discontinuity between LRDs and field galaxies, and do LRDs form a homogeneous population? In this work, we address these issues by introducing a continuous metric to evaluate the "LRDness" of galaxies. We measure their compactness ($δ_{compact}$), the sharpness of the V-shaped spectral energy distribution ($δ_{v-shape}$), and the strength of the broad Balmer line emission. We apply this approach to a sample of ~48,000 galaxies with photometric and ~5,000 with spectroscopic information, selected over ~750 arcmin^2. We find that V-shape prominence correlates strongly with morphology without a clear transition at common LRD selection thresholds: the fraction of compact galaxies rises continuously with V-shape intensity. Similarly, broad H$α$ strength increases with both V-shape sharpness and compactness. The [N II] deficit is not an exclusive feature of LRDs but a global property of compact, metal-poor galaxies. Only the 3% most extreme LRDs present a prominent Balmer break (>3) of potentially non-stellar origin. LRDs and non-LRDs follow similar trends in the evolution of the Balmer decrement with V-shape sharpness, suggesting a shared physical origin, likely dust attenuation. Estimated dust masses (~4-7 x 10^4 M_{sun}) and luminosities are low enough to account for their non-detection by ALMA. We conclude that most LRDs do not represent a separate class of objects, but rather the extreme tail of a continuous distribution of galaxies and broad H$α$ emitters, consistent with a classical broad line region and dust attenuation. |
| title | Do little red dots really form a distinct class of astronomical objects? |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2604.11677 |