Browsing by Author "Randrianjanahary, Liantsoa Finaritra"

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    Cosmological constraints using 2- and 3-point correlations with meerkat, the ska and other surveys
    (Universty of the Western Cape, 2024) Randrianjanahary, Liantsoa Finaritra; Maartens, Roy
    We explore the information from HI power spectra (tree-level and one-loop) in redshift space and bispectrum tree-level models. 21-cm emission from neutral hydrogen is a promising tool for probing the matter distribution in the universe post-reionization. The HI signals contain signatures of the primordial universe and the growth of large-scale structure in the universe. These signatures are typically analyzed via the 2-point correlation function or power spectrum. However, adding the information from the 3-point correlation function or bispectrum will be crucial to exploiting next-generation intensity mapping experiments. Upcoming surveys by SKAO and HIRAX will undertake intensive line-intensity observations, complementing galaxy surveys. This study provides new forecasts on cosmological constraints derived from the combined analysis of the 21cm power spectrum and bispectrum. We use Fisher predictions to examine how useful these surveys might be for constraining cosmological parameters, BAO distance functions, growth function, and what they mean for dynamical dark energy and modified gravity. We account for telescope beam effects, instrumental noise, foreground avoidance, the Alcock-Paczynski effect, and theoretical modeling errors in the correlators. The investigation also includes assessments of 21-cm clustering bias up to the second order.
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    Cosmology with HI intensity mapping: effect of higher order corrections
    (University of the Western Cape, 2020) Randrianjanahary, Liantsoa Finaritra; Santos, Mario
    One of the main challenges of cosmology is to unveil the nature of dark energy and dark matter. They can be constrained with baryonic acoustic oscillations (BAO) and redshift space distortions, amongst others. Both have characteristic signatures in the dark matter power spectrum. Biased tracers of dark matter, such as neutral hydrogen, are used to quantify the underlying dark matter density field. It is generally assumed that on large scales the bias of the tracer is linear. However, there is a coupling between small and large scales of the biased tracer which gives rise to a significant non-linear contribution on linear scales in the power spectrum of the biased tracer. The Hydrogen Intensity and Real-time eXperiment (HIRAX) will map the brightness temperature of neutral hydrogen (HI) over BAO scales thanks to the intensity mapping technique. We forecasted cosmological parameters for HIRAX taking into account non-linear corrections to the HI power spectrum and compared them to the linear case. We used methods based on Fisher matrices. We found values for the bias to error ratio of the cosmological parameters as high as 1 or 7, depending on the noise level. We also investigated the change in peaks location on the baryonic acoustic oscillations signal. The value of the shift goes up to Δk = 10-2h/Mpc with a reduction of amplitude of the BAO features from 16:33% to 0:33%, depending on the scales.