HI Intensity Mapping as a Test for Dark Energy

  • Kate Voller

Student thesis: Master of Philosophy


The purpose of this thesis is to find out how successfully intensity mapping can be used to measure the HI signal with upcoming interferometers. This technique is an alternative to mapping the galaxy distribution with optical redshift surveys, using the 21 cm neutral hydrogen line instead to trace the matter. It relies on detecting the combined emission from galaxies rather than being able to detect individual galaxies. In this thesis a bespoke intensity mapping instrument `Tianlai' will be compared with two interferometers not specifically designed for this purpose, namely MeerKAT and ASKAP. Several different power spectrum estimators are investigated, settling on a cross-correlation estimator. Despite needing a correction factor Fl, this estimator has the lowest noise bias at high l. A theoretical HI angular power spectrum is then used as the simulation input and the potential ability of each interferometer to recover the power spectrum is analysed. We find that integrated HI signal is able to be detected by all three interferometers after 120 hours, with good detections being made after 1200 hours. At 800 MHz (z ~ 0.8) ideal `Tianlai' and ASKAP instruments require 15 and 20 pointings while MeerKAT requires 125 pointings. This gives peak SNR values, after120 hours, of 36 and 30 for `Tianlai' and ASKAP and 20 for MeerKAT. Moving to higher frequencies (z ~ 0.4) these SNR values increase to 47, 36 and 23 for `Tianlai', ASKAP and MeerKAT respectively. As the observation time is increased, the SNR values also increase for each instrument. `Tianlai' performs best due to its many short baselines giving it improved sensitivity to the angular scales of interest. Although ASKAP and MeerKAT both have few short baselines, ASKAP's PAFs give it a very large field-of-view, resulting in it out-performing MeerKAT and having similar potential to the bespoke instrument `Tianlai'. We conclude that all three instruments would be able to make a very good detection of the integrated HI signal after 1200 hours in an ideal experiment so it would be possible to design intensity mapping experiments for all three interferometers.
Date of Award1 Aug 2015
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorRichard Battye (Supervisor)

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