Browsing by Author "Witzemann, Amadeus"

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    Cosmology with next generation radio telescopes
    (University of the Western Cape, 2019) Witzemann, Amadeus; Santos, Mario; Weltman, Amanda; Clarkson, Chris
    The next generation of radio telescopes will revolutionize cosmology by providing large three-dimensional surveys of the universe. This work presents forecasts using the technique 21cm intensity mapping (IM) combined with results from the cosmic microwave background, or mock data of galaxy surveys. First, we discuss prospects of constraining curvature independently of the dark energy (DE) model, finding that the radio instrument HIRAX will reach percent-level accuracy even when an arbitrary DE equation of state is assumed. This is followed by a study of the potential of the multi-tracer technique to surpass the cosmic variance limit, a crucial method to probe primordial non-Gaussianity and large scale general relativistic e↵ects. Using full sky simulations for the Square Kilometre Array phase 1 (SKA 1 MID) and the Large Synoptic Survey Telescope (LSST), including foregrounds, we demonstrate that the cosmic variance contaminated scenario can be beaten even in the noise free case. Finally, we derive the signal to noise ratio for the cosmic magnification signal from foreground HI intensity maps combined with background galaxy count maps. Instruments like SKA1 MID and HIRAX are highly complementary and well suited for this measurement. Thanks to the powerful design of the planned radio instruments, all results confirm their potential and promise an exciting future for cosmology.
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    MeerKLASS L-band deep-field intensity maps: entering the H I dominated regime
    (Oxford University Press, 2025) Bull, Philip; Camera, Stefano; Engelbrecht, Brandon; Fonseca, José; Irfan, Melis; Li, Yichao; Pourtsidou, Alkistis; Santos, Mario; Spinelli, Marta; Wang, Jingying; Witzemann, Amadeus
    We present results from MeerKAT single-dish HI intensity maps, the final observations to be performed in L-band in the MeerKAT Large Area Synoptic Survey (MeerKLASS) campaign. The observations represent the deepest single-dish HI intensity maps to date, produced from 41 repeated scans over 236 deg2, providing 62 h of observational data for each of the 64 dishes before flagging. By introducing an iterative self-calibration process, the estimated thermal noise of the reconstructed maps is limited to ∼ 1.21 mK (1.2 × the theoretical noise level). This thermal noise will be subdominant relative to the HI fluctuations on large scales (k ≲ 0.15 h Mpc−1), which demands upgrades to power spectrum analysis techniques, particularly for covariance estimation. In this work, we present the improved MeerKLASS analysis pipeline, validating it on both a suite of mock simulations and a small sample of overlapping spectroscopic galaxies from the Galaxy And Mass Assembly (GAMA) survey. Despite only overlapping with ∼ 25 per cent of the MeerKLASS deep field, and a conservative approach to covariance estimation, we still obtain a > 4 σ detection of the cross-power spectrum between the intensity maps and the 2269 galaxies at the narrow redshift range 0.39 < z < 0.46. We briefly discuss the HI autopower spectrum from these data, the detection of which will be the focus of follow-up work. For the first time with MeerKAT single-dish intensity maps, we also present evidence of HI emission from stacking the maps onto the positions of the GAMA galaxies.
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    Prospects for cosmic magnification measurements using H I intensity mapping
    (Oxford University Press, 2020) Witzemann, Amadeus; Pourtsidou, Alkistis; Santos, Mario G.
    We investigate the prospects of measuring the cosmic magnification effect by cross-correlating neutral hydrogen intensity mapping (H I IM) maps with background optical galaxies. We forecast the signal-to-noise ratio for H i IM data from SKA1-MID and HIRAX, combined with LSST photometric galaxy samples. We find that, thanks to their different resolutions, SKA1-MID and HIRAX are highly complementary in such an analysis. We predict that SKA1-MID can achieve a detection with a signal-to-noise ratio of ∼15 on a multipole range of ℓ ≲ 200, while HIRAX can reach a signal-to-noise ratio of ∼50 on 200 < ℓ < 2000. We conclude that measurements of the cosmic magnification signal will be possible on a wide redshift range with foreground H I intensity maps up to z ≲ 2, while optimal results are obtained when 0.6 ≲ z ≲ 1.3.