Colloquium - Measuring spatial scales in the line-to-continuum ratio from cosmic reionization in redshifted 21 cm interferometer experiments

© Colloquium

Direct detection of evolving neutral Hydrogen structures from the Cosmic Dawn and Reionization Epochs (EoR) will reveal the nature of the first stars and galaxies as well as complete our understanding of a significant evolutionary phase of the Universe. Many projects such as the MWA, LOFAR, and PAPER commenced in the last decade with the promise of high significance statistical detection of the EoR, but have so far only weakly constrained models owing to underestimation of challenges from bright foreground sources and instrument systematics. These include chromatic effects from wide-field effects, antenna apertures, reflections from the mechanical and electrical interfaces in the instrument, antenna position errors, calibration errors, etc. I will discuss a novel and a complementary approach using bi-spectrum phase that bypasses the stringent calibration requirements limiting existing approaches.

The figure shows the power spectrum of bispectrum phase on a triad of antennas as a function of line of sight spatial modes at three different redshifts using fiducial models for the EoR 21 cm temperature fluctuations and foregrounds. The separation between the red (foregrounds + noise) and gray/black curves (foregrounds + EoR + noise) at line of sight spatial scales wavenumbers > 0.5 h Mpc^-1 is a measure of the the line-to-continuum ratio of 21 cm fluctuations from the EoR and the foreground spectra on these spatial scales at different redshift/frequency bands. Such a measurement of the line-to-continuum ratio is independent of antenna calibration and errors, and can be a robust measure of the astrophysical properties which can be used to infer the presence of the EoR signal. If a reliable foreground model is available, this approach can be used to constrain the rms of 21 cm brightness temperature fluctuations from the EoR. It provides a complementary approach to verify the results from traditional approaches to detect 21 cm fluctuations from EoR using power spectrum.