arXiv subjects

Charles Mpho Takalana

Publications and source records attributed to Charles Mpho Takalana.

4 recordsLinked to original sources

arXiv2026

Variance-aware model discrimination with the Sunyaev-Zel'dovich effect of the 21 cm background (SZE-21cm)

The sky-averaged redshifted 21 cm signal from Cosmic Dawn is a uniquely sensitive tracer of early heating and ionisation, but it remains challenging to measure directly. The Sunyaev-Zel'dovich effect of the 21 cm background (SZE-21cm) provides a complementary route: Comptonisation of the incident low-frequency background by hot electrons in galaxy clusters produces a spectral distortion that can be recovered as a difference between the line of sight through a galaxy cluster and a nearby blank-sky reference, and is therefore naturally compatible with interferometric observations. We use semi-numerical simulations of the global 21 cm background, together with a relativistic scattering kernel built from the Maxwell-Juttner electron distribution, to assess how well the SZE-21cm separates physically distinct Cosmic Dawn scenarios. The model suite varies star-formation efficiency, X-ray spectral hardness, heating timing, and the suppression of low-mass sources; SZE-21cm spectra are computed over 45-200 MHz. Separability is quantified through feature-based summaries, standardised residual spectra, and a band-integrated pairwise separability index that combines seed-to-seed scatter with an astrophysical variance layer derived from coeval ON-aperture / OFF-annulus statistics. The resulting indices are intrinsic and instrument-free, and therefore upper bounds on what a real experiment with finite thermal noise can achieve. Heating-timing variations produce the strongest separations, while the X-ray hardness variations explored here are nearly degenerate with the fiducial case once the ON-OFF variance is included. We also propagate an EDGES-like benchmark curve as a morphological stress test of the framework, not as a physically validated model, illustrating how anomalous global-signal morphologies would map into the SZE-21cm.

astro-ph.CO↗

arXiv2020

Simulated differential observations of the Sunyaev-Zel'dovich Effect: Probing the Dark Ages and Epoch of Reionization

This work presents an analytical approach for studying the cosmological 21cm background signal from the Dark Ages (DA) and subsequent Epoch of Reionization (EoR). We simulate differential observations of a galaxy cluster to demonstrate how these epochs can be studied with a specific form of the Sunyaev-Zel'dovich Effect called the SZE-21cm. This work produces simulated maps of the SZE-21cm and shows that the SZE-21cm can be extracted from future observations with low-frequency radio interferometers such as the Hydrogen Epoch of Reionization Array (HERA) and the Square Kilometre Array (SKA). In order to simulate near realistic scenarios, we look into cosmic variance noise, incorporate and take into account the effects of foregrounds, thermal noise, and angular resolution for our simulated observations. We further extend this exploration by averaging over a sample of galaxy clusters to mitigate the effects of cosmic variance and instrumental noise. The impact of point source contamination is also studied. Lastly, we apply this technique to the results of the EDGES collaboration, which in 2018 reported an absorption feature of the global 21cm background signal centred at 78 MHz. The challenges to be addressed in order to achieve the objectives of this work include errors that arise due to cosmic variation, instrumental noise and point source contamination. Our approach demonstrates the potential of the SZE-21cm as an indirect probe for the DA and EoR, and we conclude that the spectral features of the SZE-21cm from our simulated observations yield results that are close to prior theoretical predictions and that the SZE-21cm can be used to test the validity of the EDGES detection.

astro-ph.CO↗

arXiv2019

Differential Observation Techniques for the SZE-21cm and radio sources

The SZE-21cm has been proposed as an alternative probe for the Dark Ages (DA) and the Epoch of Reionization (EoR). The effect is produced when photons of the 21cm background are inverse Compton (up-)scattered by electrons residing in hot plasma of cosmic structures and can be studied through differential observations of the large-scale structure, towards and away a region of the radio sky containing the cosmic structure of interest. This work makes use of the 21cmFAST code to simulate low frequency radio observations of a galaxy cluster from which we then extract the SZE-21cm signal. We further explore uses of the differential technique to radio observations of active radio galaxies using radio observations from the MWA GLEAM survey. The differential techniques this work studies enable us to extract the SZE-21cm signal from simulated galaxy cluster observations, which can then be used to obtain the global features of the 21cm signal during the DA and EoR. The technique shows further benefits in source extraction and characterisation, and feature enhancement in radio observations particularly for low-surface brightness and extended radio sources.

astro-ph.CO↗

arXiv2018

Analysis of differential observations of the cosmological radio background : studying the SZE-21cm

In pursuit of understanding the early Universe and early processes occurring particularly in the Dark Ages (DA) and the Epoch of Reionization (EoR), it is vital that a suitable probe is identified. Probing these epochs will be useful in studies of the origin of first galaxies and most importantly formation of early black-holes. Over the past decade numerous probes have been proposed, with one of the most promising being the SZE-21cm, a specific form of the Sunyaev-Zeldovich effect (SZE) produced when photons of the 21cm background are inverse Compton up-scattered by electrons residing in hot plasma of cosmic structures such as galaxy clusters and active radio galaxies. The SZE-21cm is calculated in a full relativistic approach of the scattering processes of the CMB photons modified by the cosmological redshifted 21cm background in the hot intra-cluster medium of galaxy clusters capturing effects induced by relativistic corrections to this scattering and by multiple scattering effects. We apply image differencing techniques to simulated radio observations of galaxy clusters using the redshifted 21cm background, we conduct this making use of the public semi-numeric code 21cmFAST. We are able to achieve subtraction of contaminating foregrounds through pixel by pixel operations on the data retrieved from our simulated data cubes. We demonstrate that SZE-21cm can be recovered through differential observations of the 21cm background.

astro-ph.CO↗