Prospects of Detecting HI using Redshifted 21-cm Radiation at z∼3

Abstract

Distribution of cold gas in the post-reionization era provides an important link between distribution of galaxies and the process of star formation. Redshifted 21 cm radiation from the Hyperfine transition of neutral Hydrogen allows us to probe the neutral component of cold gas, most of which is to be found in the interstellar medium of galaxies. Existing and upcoming radio telescopes can probe the large scale distribution of neutral Hydrogen via HI intensity mapping. In this paper we use an estimate of the HI power spectrum derived using an ansatz to compute the expected signal from the large scale HI distribution at z ∼ 3. We find that the scale dependence of bias at small scales makes a significant difference to the expected signal even at large angular scales. We compare the predicted signal strength with the sensitivity of radio telescopes that can observe such radiation and calculate the observation time required for detecting neutral Hydrogen at these redshifts. We find that OWFA (Ooty Wide Field Array) offers the best possibility to detect neutral Hydrogen at z ∼ 3 before the SKA (Square Kilometer Array) becomes operational. We find that the OWFA should be able to make a 3 σ or a more significant detection in 2000 hours of observations at several angular scales. Calculations done using the Fisher matrix approach indicate that a 5σ detection of the binned HI power spectrum via measurement of the amplitude of the HI power spectrum is possible in 1000 hours (Sarkar, Bharadwaj and Ali, 2017).

The Ooty Wide Field Array

“…More details regarding the predicted outcomes of observations of HI with OWFA can be found in Ali and Bharadwaj (2014); Bharadwaj et al (2015), as well as in Sarkar et al (2017). Ghelot and Bagla (2017) present a similar study of the HI signal expected to be seen by OWFA and also compare OWFA with other instruments operating in this frequency range as far as suitability for detection of HI at z∼ 3.3 is concerned.…”

“…Detailed calculations of the expected signal show that OWFA sensitivity is sufficient to make a ∼ 5σ detection of the amplitude of the power spectrum A HI of the large scale distribution of HI emission at z ∼ 3.3 in integration times of ∼ 150hr. Longer integrations (∼ 1000 hrs (Sarkar et al, 2017;Ghelot and Bagla, 2017)), should have the sensitivity to measure the power spectrum at angular scales between 11 ′ and 3 o (or wavenumbers from ∼ 0.02 to 0.5 Mpc −1 ). Two important astro-physical parameters that are constrained by these observations are the amplitude of the power spectrum A HI (which in turn depends on the cosmic density of neutral hydrogen (Ω HI ), the neutral fraction (x HI ), and the bias parameter (b HI )) and the redshift distortion parameter β (Bharadwaj et al, 2015).…”

“…Detailed calculations of the expected signal show that OWFA sensitivity is sufficient to make a ∼ 5σ detection of the amplitude of the power spectrum A HI of the large scale distribution of HI emission at z ∼ 3.3 in integration times of ∼ 150hr. Longer integrations (∼ 1000 hrs (Sarkar et al, 2017;Ghelot and Bagla, 2017)), should have the sensitivity to measure the power spectrum at angular scales between 11…”

Constraining warm dark matter power spectrum using the cross-correlation of HI 21 cm signal and the Lyman-α forest

“…The possibility of detecting the HI 21-cm signal using OWFA has been studied extensively [29,[73][74][75][76]. Detailed foreground predictions [29,77] and calibration issues [70] for OWFA have also been addressed.…”

An analytical method to simulate the H i 21-cm visibility signal for intensity mapping experiments

“…It is important and worthwhile to quantify the H i signal in terms of their expected contribution to the measured visibilities (e.g. Bharadwaj & Pandey 2003;Bharadwaj & Srikant 2004) Detailed predictions for the visibility correlations at different baselines and frequency channels for the expected statistical H i signal, foregrounds and the system noise expected at OWFA are presented in Ali & Bharadwaj (2014) and Gehlot & Bagla (2017). Theoretical estimates presented in these papers, and also direct observations (e.g.…”