Polarization leakage in epoch of reionization windows - I. Low Frequency Array observations of the 3C196 field
Number of Authors: 28
2015 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 451, no 4, 3709-3727 p.Article in journal (Refereed) Published
Detection of the 21-cm signal coming from the epoch of reionization (EoR) is challenging especially because, even after removing the foregrounds, the residual Stokes <italic toggle=yes>I maps contain leakage from polarized emission that can mimic the signal. Here, we discuss the instrumental polarization of Low Frequency Array (LOFAR) and present realistic simulations of the leakages between Stokes parameters. From the LOFAR observations of polarized emission in the 3C196 field, we have quantified the level of polarization leakage caused by the nominal model beam of LOFAR, and compared it with the EoR signal using power spectrum analysis. We found that at 134-166 MHz, within the central 4A degrees of the field the (<italic toggle=yes>Q, <italic toggle=yes>U) -> <italic toggle=yes>I leakage power is lower than the EoR signal at <italic toggle=yes>k < 0.3 Mpc(-1). The leakage was found to be localized around a Faraday depth of 0, and the rms of the leakage as a fraction of the rms of the polarized emission was shown to vary between 0.2 and 0.3 per cent, both of which could be utilized in the removal of leakage. Moreover, we could define an 'EoR window' in terms of the polarization leakage in the cylindrical power spectrum above the point spread function (PSF)-induced wedge and below <italic toggle=yes>k(ayen) similar to 0.5 Mpc(-1), and the window extended up to <italic toggle=yes>k(ayen) similar to 1 Mpc(-1) at all <italic toggle=yes>k(aSyen) when 70 per cent of the leakage had been removed. These LOFAR results show that even a modest polarimetric calibration over a field of view of a parts per thousand(2) 4A degrees in the future arrays like Square Kilometre Array will ensure that the polarization leakage remains well below the expected EoR signal at the scales of 0.02-1 Mpc(-1).
Place, publisher, year, edition, pages
2015. Vol. 451, no 4, 3709-3727 p.
polarization, instrumentation: polarimeters, intergalactic medium, cosmology: observations, dark ages, reionization, first stars
IdentifiersURN: urn:nbn:se:su:diva-121681DOI: 10.1093/mnras/stv1107ISI: 000360846400027OAI: oai:DiVA.org:su-121681DiVA: diva2:889775