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

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] lambda1486, stellar P Cygni profiles, and broad HeII lambda1640. 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* about10 8 M, and a young age of 2.4 plus or minus0.8 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 about5 Myr, and hence this system would be observed as a typical V-shaped LRD. We measure a supersolar log 10(N/O)=-0.07 plus or minus0.05 and subsolar log 10(C/O)=-0.64 plus or minus0.11; therefore log 10(N/C)=+0.58 plus or minus0.12. The independent density-sensitive NIV] λ lambda1483,1486 and CIII] λ lambda1906/1909 ratios require two zones with n e 10 6.5 cm-3 and n e 10 cubed.5 cm-3, respectively. We estimate log 10(N/C)>1.3 (2 σ) 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.