Browsing by Author "Santos, Mario G"

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    A full treatment of peculiar velocities on the reionization light cone
    (Oxford Academic, 2019) Santos, Mario G
    Accurate simulations of the 21-cm signal from the Epoch of Reionization require the generation of maps at specific frequencies given the values of astrophysical and cosmological parameters. The peculiar velocities of the hydrogen atoms producing the 21-cm radiation result in a shift in the observed frequency of the 21-cm radiation and changes the amplitude of the signal itself. This is not an effect we can remove but instead needs to be accurately modelled to ensure we infer the correct physical parameters from an observation.
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    Mitigating the effect of 1/f noise on the detection of the H I intensity mapping power spectrum from single-dish measurements
    (Oxford University Press, 2024) Irfan, Melis O; Santos, Mario G; Bull, Philip; Wang, Jingying
    We present and compare several methods to mitigate time-correlated (1/f) noise within the H I intensity mapping component of the MeerKAT Large Area Synoptic Survey (MeerKLASS). By simulating scan strategies, the H I signal, foreground emissions, white and correlated noise, we assess the ability of various data-processing pipelines to recover the power spectrum of H I brightness temperature fluctuations. We use MeerKAT pilot data to assess the level of 1/f noise expected for the MeerKLASS survey and use these measurements to create realistic levels of time-correlated noise for our simulations. We find the time-correlated noise component within the pilot data to be between 10 and 20 times higher than the white noise level at the scale of k = 0.04 Mpc−1. Having determined that the MeerKAT 1/f noise is partially correlated across all the frequency channels, we employ Singular Value Decomposition (SVD) as a technique to remove both the 1/f noise and Galactic foregrounds but find that over-cleaning results in the removal of H I power at large (angular and radial) scales; a power loss of 40 per cent is seen for a 3-mode SVD clean at the scale of k = 0.04 Mpc−1. We compare the impact of map-making using weighting by the full noise covariance (i.e. including a 1/f component), as opposed to just a simple unweighted binning, finding that including the time-correlated noise information reduces the excess power added by 1/f noise by up to 30 per cent.