Probing diffuse galactic synchrotron emission using meerkat single dish data
In recent experiments, the 21 cm neutral hydrogen (HI) line has been measured using the intensity mapping (IM) method. Measuring this HI line is a complex process because it is faint and easily contaminated by radio frequency interference (RFI) and the foregrounds. Using the MeerKLASS experiment, from the L-band (900-1670 MHz) data the 21 cm signal was probed using the single dish mode. However, initially the RFI and the most dominant foreground in our Galaxy which is the synchrotron emission had to be investigated, so they could be removed. This process also provided another validation for the existing data pipeline. As synchrotron emission is modeled using a power law, one way to probe said emission is to measure the spectral index of this power law. From the various results available in the literature, the average spectral index for frequencies that are between 0.408 and 3.8 GHz is ∼ −2.7. In this study, the MeerKLASS UHF-data (544-1087 MHz) was used alongside various ancillary experiments to probe the temperature spectral index of the synchrotron emission using the Temperature-Temperature (T-T) analysis method, as well as probing the flux density spectral index using the Spectral Energy Distribution method. From the T-T analysis, the average spectral index calculated between 45 and 923 MHz is −2.71 < β < −2.66; these results are in good agreement (within 1σ) with the existing results from Irfan et al. (2022) and Platania et al. (1998). T-T analysis between MeerKLASS and Haslam data conducted towards the lower end of the UHF-band, however, revealed a sharp and physically unlikely change in the synchrotron spectral index never before seen. This coupled with the Spectral Energy Distribution analysis revealed that further work needs to be conducted on the UHF data reduction pipeline with regards to both calibration and RFI removal. There appears to be a systematic bias in the data at a level of around 15% at the beginning of the UHF-band, decreasing to only around 5% by the end of the UHF-band when comparing these data to MeerKLASS L-Band, Haslam and OVRO-LWA data.
Cosmology, Meerklass, Diffuse emission, Single dish, Intensity mapping
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