A Little Red Dot emerging from a nitrogen-rich UV-luminous galaxy with Very Massive Stars

Abstract

JWST is revealing abundant populations of high-z galaxies with unforeseen properties: UV-luminous galaxies with high nitrogen enrichment, populations of very massive stars (VMSs; >100 M_⊙), and early forms of massive black hole growth such as the Little Red Dots (LRDs). Here we present all these phenomena appearing simultaneously in COLA1, a luminous (M_UV=−21.3) galaxy at z=6.6. New NIRSpec medium-resolution data reveal a blue UV continuum (β_UV=−2.5) with strong emission lines including NIV] λ1486, stellar P Cygni profiles, and broad HeII λ1640. We fit the UV with stellar population models, and find that the models including VMSs (limited to 300 M_⊙) are statistically preferred. The best-fit stellar population has M_*≈10⁸ M_⊙, and a young age of 2.4±0.8 Myr. The rest-optical shows a redder continuum (β_opt=−1.1) and broad Balmer lines with Balmer absorption akin to LRD spectra. By evolving the best-fit stellar population we find that the UV could dim by 1-2 mag in ∼5 Myr, and hence this system would be observed as a typical V-shaped LRD. We measure a supersolar log₁₀(N/O)=−0.07±0.05 and subsolar log₁₀(C/O)=−0.64±0.11; therefore log₁₀(N/C)=+0.58±0.12. The independent density-sensitive NIV] λλ1483,1486 and CIII] λλ1906/1909 ratios require two zones with n_e≳10^6.5 cm⁻³ and n_e≲10^3.5 cm⁻³, respectively. We estimate log₁₀(N/C)>1.3 (2σ) for the dense zone, requiring extreme N/C enrichment mechanisms such as highly rotating >100 M_⊙ VMSs, tidal disruption events, or supermassive stars. We speculate that runaway collisions of massive stars in a dense stellar cluster may have lead to the seeding of an intermediate-mass black hole resulting in the formation of an LRD.

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BibTeX RIS

BibTeX

@misc{torralba2026little,
  title = {{A Little Red Dot emerging from a nitrogen-rich UV-luminous galaxy with Very Massive Stars}},
  author = {Alberto Torralba and Jorryt Matthee and Rui Marques-Chaves and Fabrice Martins and Benjamín Navarrete and Gabriele Pezzulli and Edoardo Iani and Rohan P. Naidu and Gabriel Brammer and Claudia Di Cesare and Anne Hutter and Gauri Kotiwale and Ruari Mackenzie and Sara Mascia and Romain Meyer and Daniel Schaerer},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.29887},
  eprint = {2610.29887},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.29887},
  note = {CC BY 4.0},
}

RIS

TY  - UNPB
TI  - A Little Red Dot emerging from a nitrogen-rich UV-luminous galaxy with Very Massive Stars
AU  - Alberto Torralba
AU  - Jorryt Matthee
AU  - Rui Marques-Chaves
AU  - Fabrice Martins
AU  - Benjamín Navarrete
AU  - Gabriele Pezzulli
AU  - Edoardo Iani
AU  - Rohan P. Naidu
AU  - Gabriel Brammer
AU  - Claudia Di Cesare
AU  - Anne Hutter
AU  - Gauri Kotiwale
AU  - Ruari Mackenzie
AU  - Sara Mascia
AU  - Romain Meyer
AU  - Daniel Schaerer
PY  - 2026
DA  - 2026/10/21
PB  - arXiv
DO  - 10.48550/arxiv.2610.29887
UR  - https://arxiv.org/abs/2610.29887
AB  - JWST is revealing abundant populations of high-z galaxies with unforeseen properties: UV-luminous galaxies with high nitrogen enrichment, populations of very massive stars (VMSs; >100 M_⊙), and early forms of massive black hole growth such as the Little Red Dots (LRDs). Here we present all these phenomena appearing simultaneously in COLA1, a luminous (M_UV=−21.3) galaxy at z=6.6. New NIRSpec medium-resolution data reveal a blue UV continuum (β_UV=−2.5) with strong emission lines including NIV] λ1486, stellar P Cygni profiles, and broad HeII λ1640. We fit the UV with stellar population models, and find that the models including VMSs (limited to 300 M_⊙) are statistically preferred. The best-fit stellar population has M_*≈10^8 M_⊙, and a young age of 2.4±0.8 Myr. The rest-optical shows a redder continuum (β_opt=−1.1) and broad Balmer lines with Balmer absorption akin to LRD spectra. By evolving the best-fit stellar population we find that the UV could dim by 1-2 mag in ∼5 Myr, and hence this system would be observed as a typical V-shaped LRD. We measure a supersolar log_10(N/O)=−0.07±0.05 and subsolar log_10(C/O)=−0.64±0.11; therefore log_10(N/C)=+0.58±0.12. The independent density-sensitive NIV] λλ1483,1486 and CIII] λλ1906/1909 ratios require two zones with n_e≳10^6.5 cm^−3 and n_e≲10^3.5 cm^−3, respectively. We estimate log_10(N/C)>1.3 (2σ) for the dense zone, requiring extreme N/C enrichment mechanisms such as highly rotating >100 M_⊙ VMSs, tidal disruption events, or supermassive stars. We speculate that runaway collisions of massive stars in a dense stellar cluster may have lead to the seeding of an intermediate-mass black hole resulting in the formation of an LRD.
ER  -

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