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 Radiative Feedback of the First Cosmological Objects
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In hierarchical models of structure formation, an early cosmic UV background (UVB) is produced by the small (T_vir < 10^4 K) halos that collapse before reionization. The UVB at energies below 13.6eV suppresses the formation of stars or black holes inside small halos, by photo-dissociating their only cooling agent, molecular H2. We self-consistently compute the buildup of the early UVB in Press-Schechter models, coupled with H2 photo-dissociation both in the intergalactic medium (IGM), and inside virialized halos. We find that the intergalactic H2 has a negligible effect on the UVB, both because its initial optical depth is small (tau<0.1), and because it is photo-dissociated at an early stage. If the UV sources in the first collapsed halos are stars, then their UV flux suppresses further star-formation inside small halos. This results in a pause in the buildup of the UVB, and reionization is delayed until larger halos (T_vir> 10^4 K) collapse. If the small halos host mini-quasars with hard spectra extending to approximately 1 keV, then their X-rays balance the effects of the UVB, the negative feedback does not occur, and reionization can be caused by the small halos.
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Axion dark matter decay injects 1-13.6 eV photons that suppress H2, enabling atomic cooling halos and direct collapse black hole seeds for axion masses 24.5-26.5 eV and couplings down to 4e-12/GeV.
Cosmological hydrodynamical simulations predict that UV diversity in Little Red Dots encodes direct-collapse black hole ages via a rapid transition from BH- to stellar-dominated emission after ~30 Myr.
Lumina runs a 500 cMpc radiation-hydrodynamic simulation combining IllustrisTNG galaxy formation with six-bin M1 radiation transport to predict late stellar-driven HI reionization ending around z=4.75 and AGN-driven HeII reionization nearly complete by z=3.
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Direct Collapse Black Hole Candidates from Decaying Dark Matter
Axion dark matter decay injects 1-13.6 eV photons that suppress H2, enabling atomic cooling halos and direct collapse black hole seeds for axion masses 24.5-26.5 eV and couplings down to 4e-12/GeV.