Foregrounds with polarization states that are not smooth functions of frequency present a challenge to H i Epoch of Reionization (EOR) power spectrum measurements if they are not cleanly separated from the desired Stokes I signal. The intrinsic polarization impurity of an antenna’s electromagnetic response limits the degree to which components of the polarization state on the sky can be separated from one another, leading to the possibility that this frequency structure could be confused for H i emission. We investigate the potential of Faraday rotation by Earth’s ionosphere to provide a mechanism for both mitigation of and systematic tests for this contamination. Specifically, we consider the delay power spectrum estimator, which relies on the expectation that foregrounds will be separated from the cosmological signal by a clearly demarcated boundary in Fourier space and is being used by the Hydrogen Epoch of Reionization Array (HERA) experiment. Through simulations of visibility measurements that include the ionospheric Faraday rotation calculated from real historical ionospheric plasma density data, we find that the incoherent averaging of the polarization state over repeated observations of the sky may attenuate polarization leakage in the power spectrum by a factor of 10 or more. Additionally, this effect provides a way to test for the presence of polarized foreground contamination in the EOR power spectrum estimate. [ABSTRACT FROM AUTHOR]
Copyright of Astrophysical Journal is the property of IOP Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
