1000-10,000 M$_\odot$ Primordial Stars Created the Nitrogen Excess in GS 3073 at $z = 5.55$

TL;DR

This study addresses the origin of GS 3073's extreme nitrogen enrichment at redshift $z=5.55$ by testing whether supermassive Population III stars with masses in the range $1000$–$10^4$ M$_\odot$ can reproduce the observed N/O, C/O, and Ne/O abundance patterns. Using the GENEC stellar evolution code with a 38-isotope network and relativistic gravity corrections, the authors evolve ten SMS models under cold accretion to near the end of core O/Si burning, and compute integrated yields and dilution with ambient gas, exploring three mass-loss/dilution prescriptions. They find that N/O enrichment tracks can be reproduced within a window of $10^3$–$10^4$ M$_\odot$ SMSs, with specific masses and dilution factors aligning GS 3073's N/O, C/O, and Ne/O; stars outside this mass range cannot achieve the observed ratios. The results provide compelling fossil evidence for the existence of supermassive Pop III stars at cosmic dawn, with implications for early black hole seeding and the chemical evolution of high-redshift galaxies.

Abstract

The advent of the James Webb Space Telescope has revealed a wealth of new galaxies just a few hundred Myr after the Big Bang. Some of these galaxies exhibit unusual N/O ratios that are difficult to explain with stellar populations today. While Wolf-Rayet stars in multiple-burst populations, very massive or rapidly-rotating primordial stars, general relativistic explosions of metal-enriched supermassive stars, or the precursors of globular clusters can in principle account for the nitrogen excess in the galaxies GN-z11 and CEERS 1019, no known stars or supernovae can explain the far higher N/O ratio of 0.46 in GS 3073 at redshift $z =$ 5.55. Here we show that the extreme nitrogen abundances in GS 3073 can be produced by 1000 - 10,000 M$_{\odot}$ primordial (Pop III) stars. We find that these are the only candidates that can account for its large N/O ratios and its C/O and Ne/O ratios. GS 3073 is thus the first conclusive evidence in the fossil abundance record of the existence of supermassive Pop III stars at cosmic Dawn.

Figures (8)

• Figure 1: HR (top) and Kippenhahn diagrams (bottom) for the 7000 $M_{\odot}$ star. The entire evolution of the star is shown in (a) and (b), its pre-MS evolution is shown in (c) and (d), its core H burning phase is in (e) and (f), and core He burning to the end of Si burning are in (g) and (h). The black and white lines in the Kippenhahn diagrams are isomass and isothermal lines, respectively, and the red and green dots along the track on the lower left in (a) are the zero-age main sequence (ZAMS) positions of 2 - 120 $M_{\odot}$ and 1000 - 10,000 $M_{\odot}$ Pop III stars for comparison.
• Figure 2: Abundance profiles of the $7000\,M_\odot$ star at three evolutionary stages. Top: beginning of core He burning. Middle: middle of core He burning. Bottom: end of Si burning. Purple and yellow regions mark convective and radiative zones, respectively.
• Figure 3: Element number ratios in the star at the end of Si burning. The masses used to calculate the ratios at a mass coordinate are cumulative, from the stellar atmosphere on the right to the depth corresponding to the given mass loss on the left.
• Figure 4: N/O, C/O and Ne/O number ratios for 5 select models in the mass range of 1000 - 10,000 $M_{\odot}$ Pop III stars. Top: 10% mass loss. Center: 50% mass loss. Bottom: loss of all the mass above the CO core. The green, yellow and brown stars indicate corresponding ratios for GS 3073, CEERS 1019 and GN-z11, respectively. The dilution factor is the mass of the gas contaminated by outflows from the star divided by the mass of the outflow. Outliers appear only in the "CO core" case (bottom panel), where the mass cut can intersect the narrow N rich/O poor layer immediately outside the core; the 10% and 50% fixed fraction cases average over this gradient and exhibit much smaller scatter.
• Figure 5: Abundance ratios of 5 SMSs with contributions by the galactic stars for the case of 10% mass loss. The green, yellow and brown stars indicate corresponding ratios for GS 3073, CEERS 1019 and GN-z11, respectively. If the chemically mature stellar population contributes C, N, O, and Ne mass fractions $\chi_{\rm C} =$$2.8 \times 10^{-4}$, $\chi_{\rm N} =$$8 \times 10^{-5}$, $\chi_{\rm O} =$$1.2 \times 10^{-3}$ and $\chi_{\rm Ne} =$$9.4 \times 10^{-4}$ then all 10 models can reproduce the observed near vertical transition in N/O ratio while also explaining the C/O ratios ji24.