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Title: Intensity mapping : a new approach to probe the large-scale structure of the Universe
Author: Collis Olivari, Lucas
ISNI:       0000 0004 7225 9732
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2018
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Intensity mapping (IM) is a new observational technique to survey the large-scale structure of matter using emission lines, such as the 21 cm emission line of atomic hydrogen (HI) and the rotational lines of the carbon monoxide molecule (CO). Sensitive radio surveys have the potential to detect the HI power spectrum at low redshifts (z <1) in order to constrain the properties of dark energy and massive neutrinos. Observations of the HI signal will be contaminated by instrumental noise and, more significantly, by astrophysical foregrounds, such as the Galactic synchrotron emission, which is at least four orders of magnitude brighter than the HI signal. In this thesis, we study the ability of the Generalized Needlet Internal Linear Combination (GNILC) method to subtract radio foregrounds and to recover the cosmological HI signal for HI IM experiments. The GNILC method is a new technique that uses both frequency and spatial information to separate the components of the observed data. For simulated radio observations including HI emission, Galactic synchrotron, Galactic free-free, extragalactic point sources and thermal noise, we find that it can reconstruct the HI plus noise power spectrum with 7.0% accuracy for 0.13 <z <0.48 (960 - 1260 MHz) and l <400. In this work, GNILC is also applied to a particular CO IM experiment: the CO Mapping Array Pathfinder (COMAP). In this case, the simulated radio observations include CO emission, Galactic synchrotron, Galactic free-free, Galactic anomalous microwave emission, extragalactic point sources and thermal noise. We find that GNILC can reconstruct the CO plus noise power spectra with 7.3% accuracy for COMAP phase 1 (l <1800) and 6.3% for phase 2 (l <3000). In both cases, we have 2.4 <z <3.4 (26 - 34 GHz). In this work, we also forecast the uncertainties on cosmological parameters for the upcoming HI IM experiments BINGO (BAO from Integrated Neutral Gas Observations) and SKA (Square Kilometre Array) phase-1 dish array operating in auto-correlation mode. For the optimal case of BINGO with no foregrounds, the combination of the HI angular power spectra with Planck results allows w to be measured with a precision of 4%, while the combination of the BAO acoustic scale with Planck gives a precision of 7%. We consider a number of potentially complicating effects, including foregrounds and redshift dependent bias, which increase the uncertainty on w but not dramatically; in all cases the final uncertainty is found to be less than 8% for BINGO. For the combination of SKA-MID in auto-correlation mode (total-power) with Planck, we find that, in ideal conditions, w can be measured with a precision of 4% for the redshift range 0.35 <z <3 (350 - 1050 MHz) and 2% for 0 <z <0.49 (950 - 1421 MHz). Extending the model to include the sum of neutrino masses yields a 95% upper limit of less than 0.30 eV for BINGO and less than 0.12 eV for SKA phase 1, competitive with the current best constraints in the case of BINGO and significantly better in the case of SKA.
Supervisor: Dickinson, Clive Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Dark Energy ; Component Separation ; Radio Astronomy ; Cosmology ; Intensity Mapping