Browsing by Author "Jolicoeur, Sheean"

Now showing 1 - 5 of 5
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    Constraining primordial non-Gaussianity by combining next-generation galaxy and 21 cm intensity mapping surveys
    (Institute for Ionics, 2023) Sheean, Jolicoeur; Maartens, Roy; Jolicoeur, Sheean; Dlamini, Simthembile
    Surveys of the matter distribution contain ‘fossil’ information on possible non-Gaussianity that is generated in the primordial universe. This primordial signal survives only on the largest scales where cosmic variance is strongest. By combining different surveys in a multi-tracer approach, we can suppress the cosmic variance and significantly improve the precision on the level of primordial non-Gaussianity.We consider a combination of an optical galaxy survey, like the recently initiated DESI survey, together with a new and very different type of survey, a 21cm intensity mapping survey, like the upcoming SKAO survey. A Fisher forecast of the precision on the local primordial non-Gaussianity parameter fNL, shows that this multi-tracer combination, together with non-overlap single-tracer information, can deliver precision comparable to that from the CMB. Taking account of the largest systematic, i.e. foreground contamination in intensity mapping, we find that σ( fNL) ∼ 4
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    Constraining primordial non-gaussianity by combining next-generation galaxy and 21 cm intensity mapping surveys
    (SpringerOpen, 2023) Jolicoeur, Sheean; Maartens, Roy; Dlamini, Simthembile
    Surveys of the matter distribution contain ‘fossil’ information on possible non-Gaussianity that is generated in the primordialUniverse. This primordial signal survives only on the largest scales where cosmic variance is strongest. By combining different surveys in a multi-tracer approach, we can suppress the cosmic variance and significantly improve the precision on the level of primordial non-Gaussianity.We consider a combination of an optical galaxy survey, like the recently initiated DESI survey, together with a new and very different type of survey, a 21cm intensity mapping survey, like the upcoming SKAO survey.
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    Detecting the relativistic galaxy bispectrum
    (IOP Publishing Ltd, 2020) Maartens, Roy; Jolicoeur, Sheean; Umeh, Obinna
    The Fourier galaxy bispectrum is complex, with the imaginary part arising from leading-order relativistic corrections, due to Doppler, gravitational redshift and related lineof-sight effects in redshift space. The detection of the imaginary part of the bispectrum is potentially a smoking gun signal of relativistic contributions. We investigate whether nextgeneration spectroscopic surveys could make such a detection. For a Stage IV spectroscopic Hα survey similar to Euclid, we find that the cumulative signal to noise of this relativistic signature is O(10). Long-mode relativistic effects couple to short-mode Newtonian effects in the galaxy bispectrum, but not in the galaxy power spectrum. This is the basis for detectability of relativistic effects in the bispectrum of a single galaxy survey, whereas the power spectrum requires multiple galaxy surveys to detect the corresponding signal.
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    Multipoles of the relativistic galaxy bispectrum
    (IOP Publishing Ltd, 2020) Clarkson, Chris; de Weerd, Eline M.; Jolicoeur, Sheean
    Above the equality scale the galaxy bispectrum will be a key probe for measuring primordial non-Gaussianity which can help differentiate between different inflationary models and other theories of the early universe. On these scales a variety of relativistic effects come into play once the galaxy number-count fluctuation is projected onto our past lightcone. By decomposing the Fourier-space bispectrum into invariant multipoles about the observer’s line of sight we examine in detail how the relativistic effects contribute to these. We show how to perform this decomposition analytically, which is significantly faster for subsequent computations. While all multipoles receive a contribution from the relativistic part, odd multipoles arising from the imaginary part of the bispectrum have no Newtonian contribution, making the odd multipoles a smoking gun for a relativistic signature in the bispectrum for single tracers. The dipole and the octopole are significant on equality scales and above where the Newtonian approximation breaks down. This breakdown is further signified by the fact that the even multipoles receive a significant correction on very large scales.
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    The observed bispectrum for SKA and other galaxy surveys
    (University of the Western Cape, 2019) Jolicoeur, Sheean; Maartens, Roy; Umeh, Obinna
    Next-generation galaxy surveys will usher in a new era of high precision cosmology. They will increasingly rely on the galaxy bispectrum to provide improved constraints on the key parameters of a cosmological model to percent level or even beyond. Hereby, it is imperative to understand the theory of the galaxy bispectrum to at least the same level of precision. By this, we mean to include all the general relativistic projection effects arising from observing on the past lightcone, which still remains a theoretical challenge. This is because unlike the galaxy power spectrum, the galaxy bispectrum requires these lightcone corrections at second-order. For the rst time, this PhD project looks at all the local relativistic lightcone e ects in the galaxy bispectrum for a at Friedmann-Lemaitre-Robertson-Walker Universe, giving full details on the second-order scalars, vectors and tensors. These lightcone effects are mostly Doppler and gravitational potential contributions. The vector and tensor modes are induced at second order by scalars. We focus on the squeezed shapes for the monopole of the galaxy bispectrum because non-Gaussianity of the local form shows high signatures for these triangular con gurations. In the exact squeezed limit, the contributions from the vectors and tensors vanish. These relativistic projection effects, if not included in the analysis of observations, can be mistaken for primordial non-Gaussianity. For future surveys which will probe equality scales and beyond, all the relativistic corrections will need to be considered for an accurate measurement of primordial non-Gaussianity.