Very massive stars and nitrogen-emitting galaxies

Abstract

Recent studies of high-redshift galaxies with James Webb Space Telescope (JWST), such as GN-z11 at z = 10.6, show unexpectedly significant amounts of nitrogen (N) in their spectra. As this phenomenology appears to extend to gravitionally lensed galaxies at Cosmic noon such as the Sunburst Arc at z = 2.37, as well as globular clusters overall, we suggest that the common ingredient among them are very massive stars (VMSs) with zero-age main sequence (ZAMS) masses in the range of 100–1000 M⊙. The He II in the Sunburst Arc might also be the result of the disproportionally large contribution of VMS to the total stellar contribution. We analyse the pros and cons of the previous suggestions, including classical Wolf–Rayet (cWR) stars and supermassive stars (SMSs), to conclude that only our VMS alternative ticks all the relevant boxes. We discuss the VMS mass-loss history via their peculiar vertical evolution in the HR diagram resulting from a self-regulatory effect of these wind-dominated VMSs and we estimate that the large amounts of N present in star-forming galaxies may indeed result from VMSs. We conclude that VMSs should be included in population synthesis and chemical evolution models. Moreover, that it is critical for this to be done self-consistently, as a small error in their mass-loss rates would have dramatic consequences for their stellar evolution, as well as their ionising and chemical feedback.

Which Came First: Supermassive Black Holes or Galaxies? Insights from JWST

“…A remarkable [N/O]  + 0.6 enrichment (Cameron et al 2023) is seen in GN-z11 (Bunker et al 2023), with one of the highest confirmed spectroscopic redshifts for any galaxy. One possible source could be very massive stars with initial masses of hundreds of solar masses (Vink 2023), associated with a top-heavy IMF (Bekki & Tsujimoto 2023). An alternative could be supermassive stars (Marques-Chaves et al 2024), with initial masses of thousands of solar masses, or direct-collapse black hole precursors with masses possibly reaching 10 5 -10 6 M e .…”

“…They suggest an intimate connection between black hole feedback and rapid (massive) star formation, indicative of what is often referred to as positive feedback, because the chemical timescales must be relatively short. This connection, resulting in the speed-up of chemical evolution, would be further enhanced by including the effects of stellar tidal disruptions as suggested to account for the relative-to-solar nitrogen-to-carbon abundance ratio enhancement and abundance pattern consistent with a single stellar tidal disruption event in a nearby AGN (Miller et al 2023), or by the possible role of very massive or even supermassive stars (Marques-Chaves et al 2024;Vink 2023).…”