Foregrounds for observations of the cosmological 21 cm line: II. Westerbork observations of the fields around 3C196 and the North Celestial Pole

TL;DR

This paper presents detailed Westerbork telescope observations of foreground emissions at 140-160 MHz around 3C196 and the North Celestial Pole, crucial for future 21 cm cosmology studies, including polarization analysis and power spectra.

Contribution

It provides new high-resolution measurements of foreground intensity and polarization structures in key sky regions for 21 cm cosmology, aiding foreground subtraction strategies.

Findings

Characterized foreground structures at 1-30 arcmin scales.

Analyzed polarization using rotation measure synthesis.

Achieved high dynamic range calibration of total intensity maps.

Abstract

In the coming years a new insight into galaxy formation and the thermal history of the Universe is expected to come from the detection of the highly redshifted cosmological 21 cm line. The cosmological 21 cm line signal is buried under Galactic and extragalactic foregrounds which are likely to be a few orders of magnitude brighter. Strategies and techniques for effective subtraction of these foreground sources require a detailed knowledge of their structure in both intensity and polarization on the relevant angular scales of 1-30 arcmin. We present results from observations conducted with the Westerbork telescope in the 140-160 MHz range with 2 arcmin resolution in two fields located at intermediate Galactic latitude, centred around the bright quasar 3C196 and the North Celestial Pole. They were observed with the purpose of characterizing the foreground properties in sky areas where actual observations of the cosmological 21 cm line could be carried out. The polarization data were analysed through the rotation measure synthesis technique. We have computed total intensity and polarization angular power spectra. Total intensity maps were carefully calibrated, reaching a high dynamic range, 150000:1 in the case of the 3C196 field. [abridged]