Active galactic nuclei-heated dust revealed in "little red dots"
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| Main Authors: | , , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| author | Delvecchio, I. Daddi, E. Magnelli, B. Elbaz, D. Giavalisco, M. Traina, A. Lanzuisi, G. Akins, H. B. Belli, S. Casey, C. M. Gentile, F. Gruppioni, C. Pozzi, F. Zamorani, G. |
| author_facet | Delvecchio, I. Daddi, E. Magnelli, B. Elbaz, D. Giavalisco, M. Traina, A. Lanzuisi, G. Akins, H. B. Belli, S. Casey, C. M. Gentile, F. Gruppioni, C. Pozzi, F. Zamorani, G. |
| contents | Little red dots (LRDs) are a puzzling population of extragalactic sources whose origin is highly debated. In this {work}, we performed a comprehensive stacking analysis of NIRCam, MIRI, and ALMA images of a large and homogeneously selected sample of LRDs from multiple JWST Legacy fields. We report clear evidence of hot-dust emission in the median stacked spectral energy distribution (SED) that features a rising near-infrared continuum up to rest-frame $λ_{\rm rest}$$\sim$ 3$μ$m, which is best explained by a standard dusty active galactic nucleus (AGN) structure. Although LRDs are likely to be a heterogeneous population, our findings suggest that most ($\gtrsim$50 %) LRDs show AGN-heated dust emission, regardless of whether the optical and ultraviolet (UV) continua are stellar or AGN-dominated. In either case, the best-fit dusty-AGN SED, combined with the lack of X-ray detection in the deep Chandra stacks, suggests that Compton-thick ($N_{\rm H}$$>$3$\times$10$^{24}$ cm$^{-2}$) gas obscuration is common, and likely confined within the dust sublimation radius ($R$$_{\rm sub}$$\sim$0.1 pc). Therefore, we argue that AGN-heated dust does not directly obscure either the optical-UV continuum or the broad-line region emission, in order to explain the observed blue UV slopes and prominent Balmer features. While a gas-dust displacement is in line with several models, the formation scenario (in-situ or ex-situ) of this pre-enriched hot dust remains unclear. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2509_07100 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Active galactic nuclei-heated dust revealed in "little red dots" Delvecchio, I. Daddi, E. Magnelli, B. Elbaz, D. Giavalisco, M. Traina, A. Lanzuisi, G. Akins, H. B. Belli, S. Casey, C. M. Gentile, F. Gruppioni, C. Pozzi, F. Zamorani, G. Astrophysics of Galaxies Little red dots (LRDs) are a puzzling population of extragalactic sources whose origin is highly debated. In this {work}, we performed a comprehensive stacking analysis of NIRCam, MIRI, and ALMA images of a large and homogeneously selected sample of LRDs from multiple JWST Legacy fields. We report clear evidence of hot-dust emission in the median stacked spectral energy distribution (SED) that features a rising near-infrared continuum up to rest-frame $λ_{\rm rest}$$\sim$ 3$μ$m, which is best explained by a standard dusty active galactic nucleus (AGN) structure. Although LRDs are likely to be a heterogeneous population, our findings suggest that most ($\gtrsim$50 %) LRDs show AGN-heated dust emission, regardless of whether the optical and ultraviolet (UV) continua are stellar or AGN-dominated. In either case, the best-fit dusty-AGN SED, combined with the lack of X-ray detection in the deep Chandra stacks, suggests that Compton-thick ($N_{\rm H}$$>$3$\times$10$^{24}$ cm$^{-2}$) gas obscuration is common, and likely confined within the dust sublimation radius ($R$$_{\rm sub}$$\sim$0.1 pc). Therefore, we argue that AGN-heated dust does not directly obscure either the optical-UV continuum or the broad-line region emission, in order to explain the observed blue UV slopes and prominent Balmer features. While a gas-dust displacement is in line with several models, the formation scenario (in-situ or ex-situ) of this pre-enriched hot dust remains unclear. |
| title | Active galactic nuclei-heated dust revealed in "little red dots" |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2509.07100 |