Speaker
Description
One of the primary challenges of 21 cm cosmology analyses is overcoming calibration error. Established calibration approaches in the field require an exquisitely accurate sky model. Even low-level sky model errors introduce calibration errors that corrupt the cosmological signal and prevent a detection. We present a novel approach called Delay-Weighted Calibration, or DWCal. DWCal enables precise calibration even in the presence of sky model error. In simulation, DWCal substantially outperforms traditional sky-based calibration when the calibration sky model has realistic levels of error.
21 cm cosmology efforts are predicated on the principle that the faint cosmological signal can be separated from bright foreground emission based on its unique spectral properties. Foreground emission is spectrally smooth and therefore compact in power spectrum space, occupying a limited number of power spectrum modes known as the “foreground wedge.” However, typical calibration approaches extend this error beyond the foreground wedge into the “EoR window,” contaminating the cosmological measurement. We show that, in simulation, DWCal mitigates the impact of sky model error in calibration and reduces contamination of 21 cm measurements.
DWCal exploits the fact that sky model error is compact in power spectrum space to avoid coupling error in the foreground wedge into the EoR window. It quantifies the expected sky model error in each power spectrum mode and incorporates this information into the calibration operation. DWCal imposes no prior assumptions about the instrument’s bandpass response and can accurately calibrate even when the instrumental bandpass has substantial frequency structure. It fits the same number of free calibration parameters as traditional sky-based calibration, avoiding the computational challenges, over-fitting concerns, and degeneracies associated with many-parameter calibration approaches. The DWCal approach can be combined with other advanced calibration techniques such as redundant calibration, for which it improves the accuracy of the absolute calibration step.
