Simulated Intensity Maps from SPHEREx Mission During Cosmic Reionization
Researchers have simulated multiple emission line intensity maps observable by the SPHEREx space telescope during cosmic reionization, finding that cross-correlating lines such as Hα and [OIII] can achieve signal-to-noise ratios as high as 99. The study addresses a core challenge in intensity mapping — contamination from foreground galaxies at lower redshifts — by focusing on cross-correlations between different spectral lines rather than auto-power spectra. The findings help define what SPHEREx can realistically detect during reionization and identify where more sensitive future instruments will be needed.
A new preprint submitted to the Journal of Cosmology and Astroparticle Physics simulates Lyα, Hα, Hβ, [OII], and [OIII] intensity maps that the SPHEREx satellite could observe during the epoch of cosmic reionization. The simulations incorporate all major emission sources, radiative transfer for Lyα, and a dust extinction model calibrated on galaxies at redshift below 5. By cross-correlating line pairs rather than relying on auto-power spectra, the study effectively removes contamination from interloping foreground galaxies. The highest signal-to-noise ratio found — up to 99 — comes from cross-correlating Hα with [OIII] at z=5 under a no-dust-extinction assumption, while some line combinations are predicted to be undetectable. The dominant noise source across most scales is the instrument itself, except for Lyα and [OII] at the largest scales where interloper galaxies dominate. Intensity mapping enables probing galaxies with masses below 4×10¹⁰ solar masses that are too faint for direct SPHEREx detection, though the bulk of the observable signal comes from larger, directly detectable galaxies. Detecting the clustering signal from other lines or at redshifts above 6 will require more sensitive instruments such as the proposed Cosmic Dawn Intensity Mapper.
What's missing
The study relies on a simplified dust extinction model based on galaxies at z<5, and the authors do not fully quantify how uncertainties in dust properties at higher redshifts could affect their signal-to-noise predictions. The simulations also assume specific galaxy formation and emission models whose systematic uncertainties relative to real SPHEREx observations are not exhaustively characterized. Additionally, the paper has not yet undergone peer review.
What different sources said
- arXiv astro-phCenter
On Cross-Correlating Line Intensity Maps from SPHEREx during Reionization
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