1 Introduction

 

Our knowledge of the Galactic magnetic field at present is primarily based on studies of the distribution of rotation measures of pulsars or extragalactic sources and optical observations of polarized star light (e.g. Wielebinski 1992; Beck et al. 1996). In addition, early radio polarization surveys at low frequencies have revealed substantial linear polarization from the diffuse Galactic emission, implying the general presence of ordered magnetic fields. However, these early results were limited by low angular resolution and sensitivity. Also Faraday rotation effects are significant at low frequencies.

A polarimetric survey of the northern Galactic plane has been made by Junkes et al. (1987a) and Duncan et al. (1999) at 2695 MHz with the Effelsberg 100-m telescope. Complementary observations have been made with the Parkes 64-m telescope of a strip of the southern Galactic plane at 2400 MHz by Duncan et al. (1997). These observations revealed polarized emission of the diffuse Galactic radiation. At least some of these emission features are believed to originate at distances up to a few kpc (Junkes et al. 1987b). The medium and high latitudes of the Galaxy have not been studied in a systematic way. Surprisingly, observations at 327 MHz by Wieringa et al. (1993) carried out with the Westerbork radio telescope revealed filamentary polarized structures on a degree scale. These high Galactic latitude features are not detected at higher frequencies and have no counterpart in total intensity. Recently, Gray et al. (1998) detected at 1.4 GHz an interstellar Faraday rotation feature about $2\hbox{$^\circ$}$ in size located in front of the prominent Hii region W5. These results call for a systematic observational approach.

There exists already a Galactic plane survey at 1.4 GHz (Reich et al. 1990a, 1997), carried out with the Effelsberg telescope, which covers absolute Galactic latitudes of $4\hbox{$^\circ$}$. However, this survey does not include measurements of linearly polarized intensities. Meanwhile, a new sensitive receiver is available and we have started a sensitive survey of the radio continuum and polarized emission at medium Galactic latitudes with the Effelsberg telescope.

In a first paper (Uyaniker et al. 1998, Paper I), we have described the methods of observation and data reduction. In addition, we explained the procedure of absolute calibration of both the total intensity data from the Stockert 1.4 GHz survey (Reich 1982; Reich & Reich 1986) and the linear polarization data by 1.4 GHz observations made with the Dwingeloo 25-m telescope (Brouw & Spoelstra 1976). The medium latitude Effelsberg survey aims to observe regions at Galactic latitudes ($\vert b \vert \leq 20\hbox{$^\circ$}$) accessible to the telescope.

The areas presented in this paper cover four fields. From the first Galactic quadrant an area of $10\hbox{$^\circ$}\times 16\hbox{$^\circ$}$ centered on $\ell = 50\hbox{$^\circ$},\ b = 12\hbox{$^\circ$}$ has been observed. Here the Dwingeloo polarization data could not be used because of a low S/N-ratio in general. The Cygnus-X area is the second region. This field includes the Cygnus superbubble, which is particularly bright in X-ray emission. The third area is the highly polarized region just above the Galactic plane between $140\hbox{$^\circ$}\leq \ell \leq 153\hbox{$^\circ$}$. In the anticentre a field of $20\hbox{$^\circ$}\times 11\hbox{$.\!\!^\circ$}2$ centered on $\ell = 200\hbox{$^\circ$}$, $b = 9\hbox{$.\!\!^\circ$}4$ was surveyed. For this region no Dwingeloo polarization data are available for an absolute calibration.

In Sect. 2 we summarize some technical aspects. In Sect. 3 we show that the total intensity data are limited by confusion and we compare counts of compact sources with those based on the recent 1.4 GHz NVSS survey. The total intensity and polarimetric observations are displayed in Sect. 4, where in addition some comments on the individual fields are given.