Shot noise and scatter in the star formation efficiency as a source of 21-cm fluctuations

Abstract

The 21-cm signal from cosmic dawn and the epoch of reionization (EoR) probes the characteristics of the high redshift galaxy population. Many of the astrophysical properties of galaxies at high redshifts are currently unconstrained due to the lack of observations. This creates a vast space of possible astrophysical scenarios where the 21-cm signal needs to be modeled in order to plan for, and eventually fit, future observations. This is done with fast numerical methods which make simplifying approximations for the underlying physical processes. In this work we quantify the effect of Poisson fluctuations and scatter in the star formation efficiency; while Poisson fluctuations are included in some works and not in others, scatter in the star formation efficiency is usually neglected, and all galaxies of a given mass are assumed to have the same properties. We show that both features can have a significant effect on the 21-cm power spectrum, most importantly in scenarios where the signal is dominated by massive galaxies. Scatter in the star formation efficiency does not simply enhance the effect of Poisson fluctuations; for example we show that the power spectrum shape at cosmic dawn has a feature corresponding to the width of the galaxy brightness distribution. We also discuss some of the consequences for 21-cm imaging, and the signature of reduced correlation between the density and radiation fields.

Submitted to MNRAS on June 7th

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• LIMFAST. I. A Semi-Numerical Tool for Line Intensity Mapping
• The importance of stochasticity in determining galaxy emissivities and UV LFs during cosmic dawn and reionization
• Signatures of Cosmic Ray Heating in 21-cm Observables
• Exploiting synergies between JWST and cosmic 21-cm observations to uncover star formation in the early Universe
• Cosmic mysteries and the hydrogen 21-cm line: bridging the gap with lunar observations
• The mass distribution of the first stars can be determined via the 21-cm signal
• Effects of chemically homogeneous evolution of the first stars on the 21-cm signal and reionization
• From Dark Matter Minihalos to Large-Scale Radiative Feedback: A Self-Consistent 3D Simulation of the First Stars and Galaxies using Neural Networks
• Effect of the cosmological transition to metal-enriched star-formation on the hydrogen 21-cm signal