21cmEMUv3 emulates the cylindrical 21cm power spectrum via score-based diffusion and six other 21cmFAST observables via LSTM networks at sub-percent accuracy, then uses the emulator to infer a lower limit on soft-band X-ray luminosity from HERA data.
The X-ray spectra of the first galaxies: 21cm signatures
4 Pith papers cite this work. Polarity classification is still indexing.
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Pith papers citing it
abstract
The cosmological 21cm signal is a physics-rich probe of the early Universe, encoding information about both the ionization and the thermal history of the intergalactic medium (IGM). The latter is likely governed by X-rays from star-formation processes inside very high redshift (z > 15) galaxies. Due to the strong dependence of the mean free path on the photon energy, the X-ray SED can have a significant impact on the interferometric signal from the cosmic dawn. Recent Chandra observations of nearby, star-forming galaxies show that their SEDs are more complicated than is usually assumed in 21cm studies. In particular, these galaxies have ubiquitous, sub-keV thermal emission from the hot interstellar medium (ISM), which generally dominates the soft X-ray luminosity (with energies < 1 keV, sufficiently low to significantly interact with the IGM). Using illustrative soft and hard SEDs, we show that the IGM temperature fluctuations in the early Universe would be substantially increased if the X-ray spectra of the first galaxies were dominated by the hot ISM, compared with X-ray binaries with harder spectra. The associated large-scale power of the 21cm signal would be higher by roughly a factor of three. More generally, we show that the peak in the redshift evolution of the large-scale (k = 0.2 1/Mpc) 21cm power is a robust probe of the soft-band SED of the first galaxies, and importantly, is not degenerate with their bolometric luminosities. On the other hand, the redshift of the peak constrains the X-ray luminosity and halo masses which host the first galaxies.
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2026 4verdicts
UNVERDICTED 4representative citing papers
Simulations show recombination-weighted clumping is systematically lower than density-based measures, density-only prescriptions overpredict rates by 1.29-1.84 depending on redshift, and a new phase-space clumping factor isolates thermal and ionization effects at fixed density.
The Lumina simulation shows that explicit light-cone integrations produce a CMB optical depth 7% higher than volume-weighted ionization histories, with the excess accumulating near redshift 8 and mass-weighted estimates capturing most of the difference.
A review chapter summarizing theoretical 21-cm signatures from Cosmic Dawn and Reionization and their detectability with SKA-Low.
citing papers explorer
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21cmEMUv3: a hybrid diffusion-LSTM emulator of 21cmFAST summary observables
21cmEMUv3 emulates the cylindrical 21cm power spectrum via score-based diffusion and six other 21cmFAST observables via LSTM networks at sub-percent accuracy, then uses the emulator to infer a lower limit on soft-band X-ray luminosity from HERA data.
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The Lumina Project: Intergalactic Clumping and Recombination Sinks
Simulations show recombination-weighted clumping is systematically lower than density-based measures, density-only prescriptions overpredict rates by 1.29-1.84 depending on redshift, and a new phase-space clumping factor isolates thermal and ionization effects at fixed density.
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The Lumina Project: CMB Optical Depth Fluctuations from Patchy Reionization
The Lumina simulation shows that explicit light-cone integrations produce a CMB optical depth 7% higher than volume-weighted ionization histories, with the excess accumulating near redshift 8 and mass-weighted estimates capturing most of the difference.
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High-Redshift Signatures from the Cosmic Dawn and the Epoch of Reionization
A review chapter summarizing theoretical 21-cm signatures from Cosmic Dawn and Reionization and their detectability with SKA-Low.