The Impact of HI in Galaxies on 21-cm Intensity Fluctuations During the Reionisation Epoch

Abstract

We investigate the impact of neutral hydrogen (HI) in galaxies on the statistics of 21-cm fluctuations using analytic and semi-numerical modelling. Following the reionisation of hydrogen the HI content of the Universe is dominated by damped absorption systems (DLAs), with a cosmic density in HI that is observed to be constant at a level equal to ~2% of the cosmic baryon density from z~1 to z~5. We show that extrapolation of this constant fraction into the reionisation epoch results in a reduction of 10-20% in the amplitude of 21-cm fluctuations over a range of spatial scales. The assumption of a different percentage during the reionisation era results in a proportional change in the 21-cm fluctuation amplitude. We find that consideration of HI in galaxies/DLAs reduces the prominence of the HII region induced shoulder in the 21-cm power spectrum (PS), and hence modifies the scale dependence of 21-cm fluctuations. We also estimate the 21cm-galaxy cross PS, and show that the cross PS changes sign on scales corresponding to the HII regions. From consideration of the sensitivity for forthcoming low-frequency arrays we find that the effects of HI in galaxies/DLAs on the statistics of 21-cm fluctuations will be significant with respect to the precision of a PS or cross PS measurement. In addition, since overdense regions are reionised first we demonstrate that the cross-correlation between galaxies and 21-cm emission changes sign at the end of the reionisation era, providing an alternative avenue to pinpoint the end of reionisation. The sum of our analysis indicates that the HI content of the galaxies that reionise the universe will need to be considered in detailed modelling of the 21-cm intensity PS in order to correctly interpret measurements from forthcoming low-frequency arrays.

11 pages, 6 figures. Submitted to MNRAS

References in corpus (19)

• Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
• Cosmology at Low Frequencies: The 21 cm Transition and the High-Redshift Universe
• Constraining the Evolution of the Ionizing Background and the Epoch of Reionization with z ~ 6 Quasars II: A Sample of 19 Quasars
• Cosmological Parameter Estimation Using 21 cm Radiation from the Epoch of Reionization
• Efficient Simulations of Early Structure Formation and Reionization
• The End of the Reionization Epoch Probed by Ly-alpha Emitters at z=6.5 in the Subaru Deep Field
• Simulations and Analytic Calculations of Bubble Growth During Hydrogen Reionization
• On using visibility correlations to probe the HI distribution from the dark ages to the present epoch I: Formalism and the expected signal
• Baryonic Acoustic Oscillations in 21cm Emission: A Probe of Dark Energy out to High Redshifts
• Probing Reionization with the 21 cm-Galaxy Cross Power Spectrum
• Cosmic Reionization Redux
• The Impact of a Percolating IGM on Redshifted 21 cm Observations of Quasar HII Regions
• The Cross-Correlation of High-Redshift 21 cm and Galaxy Surveys
• Current models of the observable consequences of cosmic reionization and their detectability
• Constraints on Fundamental Cosmological Parameters with Upcoming Redshifted 21 cm Observations
• The correlation between the distribution of galaxies and 21cm emission at high redshifts
• Feedback from Clustered Sources During Reionization
• On Correlated Random Walks and 21-cm Fluctuations During Cosmic Reionization
• A Method to Measure the Mass of Damped Ly-alpha Absorber Host Galaxies Using Fluctuations in 21cm Emission

Cited by in corpus (6)

• Reionization and Cosmology with 21 cm Fluctuations
• Discovery of a redshift 6.13 quasar in the UKIRT Infrared Deep Sky Survey
• The distribution of Lyman-limit absorption systems during and after reionization
• The spatial distribution of neutral hydrogen as traced by low HI mass galaxies
• 21-cm signatures of residual HI inside cosmic HII regions during reionization
• The Shocking Truth: The small contribution to hydrogen reionization from gravitational infall