JWST-JADES. Possible Population III signatures at z=10.6 in the halo of GN-z11 (2306.00953v3)

Abstract: Finding the first generation of stars formed out of pristine gas in the early Universe, known as Population III (PopIII) stars, is one of the most important goals of modern astrophysics. Recent models have suggested that PopIII stars may form in pockets of pristine gas in the halo of more evolved galaxies. We present NIRSpec integral field spectroscopy and micro-shutter array spectroscopic observations of the region around GN-z11, an exceptionally luminous galaxy at z=10.6, that reveal a greater than 5 sigma detection of a feature consistent with being HeII1640 emission at the redshift of GN-z11. The very high equivalent width of the putative HeII emission in this clump (log(EW_rest(HeII)/A) = 1.79) and a lack of metal lines can be explained in terms of photoionisation by PopIII stars, while photoionisation by PopII stars is inconsistent with the data. The high equivalent width would also indicate that the putative PopIII stars likely have an initial mass function with an upper cutoff reaching at least 500 Msun. The PopIII bolometric luminosity inferred from the HeII line would be 7 x 10^9 Lsun, which would imply a total stellar mass formed in the burst of about 2 x 10^5 Msun. We find that photoionisation by the active galactic nucleus (AGN) in GN-z11 cannot account for the HeII luminosity observed in the clump but can potentially be responsible for an additional HeII emission observed closer to GN-z11. We also consider the possibility of in situ photoionisation by an accreting direct collapse black hole hosted by the HeII clump. We find that this scenario is less favoured, but it remains a possible alternative interpretation. We also report the detection of a Ly-alpha halo stemming out of GN-z11 and extending out to about 2 kpc as well as resolved funnel-shaped CIII emission likely tracing the ionisation cone of the AGN.

• The paper presents a >5σ detection of HeII1640 emission, indicating potential Population III star signatures in GN-z11's halo.
• The study utilizes JWST NIRSpec observations, revealing a high equivalent width and a top-heavy IMF with masses up to 500 M☉ in a low-metallicity environment.
• Alternate phenomena such as AGN photoionization were ruled out due to insufficient luminosity, supporting the in-situ formation of PopIII stars.

Analyzing Potential Population III Signatures at Redshift 10.6

The paper of Population III (PopIII) stars, believed to be the first generation of stars formed in the Universe, is crucial for our understanding of cosmic history. These stars formed from pristine hydrogen and helium gas and have eluded direct observation. This essay discusses the paper on potential signatures of PopIII stars located at a redshift of 10.6 in the halo of the galaxy GN-z11, utilizing data from the James Webb Space Telescope (JWST) Advanced Deep Extragalactic Survey (JADES).

Key Findings

This paper, based on JWST NIRSpec-IFU and NIRSpec-MSA observations, presents evidence for the existence of PopIII star signatures in GN-z11. The spectral data reveals a greater than 5σ detection of a feature consistent with HeII$\lambda$1640 emission at GN-z11's redshift. Notably, the detected HeII emission has an exceptionally high equivalent width and is unaccompanied by metal emission lines, aligning with predictions for PopIII stars, which suggest that their ionizing spectrum can doubly ionize helium due to their high temperatures.

Theoretical Implications

The presence of such strong HeII emission supports the hypothesis that PopIII stars dominate in environments of low metallicity. The top-heavy initial mass function (IMF) inferred, with an upper cutoff reaching at least 500 M$_\odot$, suggests that these massive stars significantly contribute to the observed emission features. Moreover, the inferred bolometric luminosity and stellar mass imply a substantial stellar formation event—an intriguing find in the context of dramatic evolution scenarios at such an early universe stage.

Considerations on AGN and DCBHs

The paper examines other potential phenomena that could account for the HeII emission, such as photoionization by an active galactic nucleus (AGN) or a direct collapse black hole (DCBH). However, these scenarios are shown to be less consistent with the observations. Particularly, the HeII luminosity from AGN photoionization falls short by two orders of magnitude, suggesting that in-situ emission by massive PopIII stars is a more likely explanation.

Detection of Lyα Halo and Other Emission Lines

The data also reveals a Lyα halo extending approximately 2 kpc and a funnel-shaped CIII] emission, likely reflecting the ionization cone from the GN-z11 AGN. These observations provide further insights into the galactic ionization mechanisms during the epoch of reionization.

Future Implications

The detection of PopIII stars can have significant implications for our understanding of early star formation processes and cosmic reionization. This paper underscores the capabilities of the JWST in probing high-redshift galaxies and opens avenues for further investigation into the nature and distribution of PopIII stars across different cosmic environments. Future developments could explore more advanced simulations and refine our models of star formation in the early universe, driving an enhanced understanding of primordial galaxy formation and evolution.

In conclusion, these findings mark a significant step towards unraveling the properties of Population III stars and contribute vital knowledge to the astrophysical community, providing compelling evidence of early stellar formation in the universe.