arXiv subjects

Paul M. Geil

Publications and source records attributed to Paul M. Geil.

21 records · Page 2Linked to original sources

arXiv2009

Measurement of the baryonic acoustic oscillation scale in 21 cm intensity fluctuations during the reionisation era

It has recently been suggested that the power spectrum of redshifted 21cm fluctuations could be used to measure the scale of baryonic acoustic oscillations (BAOs) during the reionisation era. The resulting measurements are potentially as precise as those offered by the next generation of galaxy redshift surveys at lower redshift. However unlike galaxy redshift surveys, which in the linear regime are subject to a scale independent galaxy bias, the growth of ionised regions during reionisation is thought to introduce a strongly scale dependent relationship between the 21cm and mass power spectra. We use a semi-numerical model for reionisation to assess the impact of ionised regions on the precision and accuracy with which the BAO scale could be measured using redshifted 21cm observations. For a model in which reionisation is completed at z~6, we find that the constraints on the BAO scale are not systematically biased at z > 6.5. In this scenario, and assuming the sensitivity attainable with a low-frequency array comprising 10 times the collecting area of the Murchison Widefield Array, the BAO scale could be measured to within 1.5 per cent in the range 6.5 < z < 7.5.

astro-ph↗

arXiv2008

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

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.

astro-ph↗

arXiv2008

The Impact of a Percolating IGM on Redshifted 21 cm Observations of Quasar HII Regions

We assess the impact of inhomogeneous reionization on detection of HII regions surrounding luminous high redshift quasars using planned low frequency radio telescopes. Our approach is to implement a semi-numerical scheme to calculate the 3-dimensional structure of ionized regions surrounding a massive halo at high redshift, including the ionizing influence of a luminous quasar. As part of our analysis we briefly contrast our scheme with published semi-numerical models. We calculate mock 21cm spectra along the line of sight towards high redshift quasars, and estimate the ability of the planned Murchison Widefield Array to detect the presence of HII regions. The signal-to-noise for detection will drop as the characteristic bubble size grows during reionization because the quasar's influence becomes less prominent. However, quasars will imprint a detectable signature on observed 21cm spectra that is distinct from a region of typical IGM. At epochs where the mean hydrogen neutral fraction is ~30% or greater we find that neutral gas in the IGM surrounding a single quasar will be detectable (at a significance of 5 sigma) within 100 hour integrations in more than 50% of cases. 1000 hour integrations will be required to detect a smaller neutral fraction of 15% in more than 50% of cases. A highly significant detection will be possible in only 100 hours for a stack of 10 smaller 3 proper Mpc HII regions. The accurate measurement of the global average neutral fraction ( ) will be limited by systematic fluctuations between lines of sight for single HII regions. We estimate the accuracy with which the global neutral fraction could be measured from a single HII region to be 50%, 30% and 20% for ~ 0.15, 0.3 and 0.5 respectively.

astro-ph↗