The Pristine HeII Emitter near GN-z11: Constraining the Mass Distribution of the First Stars
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| Format: | Preprint |
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2026
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| _version_ | 1866918465662615552 |
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| author | Rusta, Elka Salvadori, Stefania Maiolino, Roberto Gelli, Viola Koutsouridou, Ioanna Carniani, Stefano Übler, Hannah Marconi, Alessandro Schaerer, Daniel |
| author_facet | Rusta, Elka Salvadori, Stefania Maiolino, Roberto Gelli, Viola Koutsouridou, Ioanna Carniani, Stefano Übler, Hannah Marconi, Alessandro Schaerer, Daniel |
| contents | The properties of the first metal-free stars remain largely unknown, and so far, the only data-driven constraints on their mass distribution (IMF) come from near-field cosmology. Here, we interpret new observations of the C1 and C2 components of Hebe, the HeII emitter near the galaxy GN-z11. Using a locally calibrated model, we robustly confirm the pristine (PopIII) nature of both components, showing that the measured upper limits on metal lines can only be reproduced by galaxies with $>50\%$ of their stellar mass in PopIII stars. We find that C1 is consistent with a purely PopIII system and adopt a simple parametric approach to infer the implications for the PopIII IMF and stellar mass. The observed $\rm HeII/H_γ$ ratio excludes steep IMFs, favoring top-heavy distributions, especially for young stellar ages ($\leq 1$ Myr). Combined with the HeII luminosity, this implies a total PopIII stellar mass of $2 \cdot 10^4 < M_\star/M_\odot < 6 \cdot 10^5$. While degeneracies between IMF, stellar mass, and age remain, adopting the lower stellar masses predicted by simulations ($M_\star < 10^5\,M_\odot$) strengthens the preference for top-heavy IMFs. Combining these results with near-field constraints, which instead exclude the flattest IMFs, we define a data-driven range of viable PopIII IMFs, linking characteristic mass and slope. This work demonstrates that direct observations of high-$z$ PopIII systems can place independent constraints on the IMF of the first stars, opening a new window on their formation and properties. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2603_20363 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | The Pristine HeII Emitter near GN-z11: Constraining the Mass Distribution of the First Stars Rusta, Elka Salvadori, Stefania Maiolino, Roberto Gelli, Viola Koutsouridou, Ioanna Carniani, Stefano Übler, Hannah Marconi, Alessandro Schaerer, Daniel Astrophysics of Galaxies Cosmology and Nongalactic Astrophysics Solar and Stellar Astrophysics The properties of the first metal-free stars remain largely unknown, and so far, the only data-driven constraints on their mass distribution (IMF) come from near-field cosmology. Here, we interpret new observations of the C1 and C2 components of Hebe, the HeII emitter near the galaxy GN-z11. Using a locally calibrated model, we robustly confirm the pristine (PopIII) nature of both components, showing that the measured upper limits on metal lines can only be reproduced by galaxies with $>50\%$ of their stellar mass in PopIII stars. We find that C1 is consistent with a purely PopIII system and adopt a simple parametric approach to infer the implications for the PopIII IMF and stellar mass. The observed $\rm HeII/H_γ$ ratio excludes steep IMFs, favoring top-heavy distributions, especially for young stellar ages ($\leq 1$ Myr). Combined with the HeII luminosity, this implies a total PopIII stellar mass of $2 \cdot 10^4 < M_\star/M_\odot < 6 \cdot 10^5$. While degeneracies between IMF, stellar mass, and age remain, adopting the lower stellar masses predicted by simulations ($M_\star < 10^5\,M_\odot$) strengthens the preference for top-heavy IMFs. Combining these results with near-field constraints, which instead exclude the flattest IMFs, we define a data-driven range of viable PopIII IMFs, linking characteristic mass and slope. This work demonstrates that direct observations of high-$z$ PopIII systems can place independent constraints on the IMF of the first stars, opening a new window on their formation and properties. |
| title | The Pristine HeII Emitter near GN-z11: Constraining the Mass Distribution of the First Stars |
| topic | Astrophysics of Galaxies Cosmology and Nongalactic Astrophysics Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2603.20363 |