4 Results

  We present the results of our observations in the form of contour and grey-scale maps. The maps are also available in FITS-format via Internet (http://www.mpifr-bonn.mpg.de/survey.html).

When adding the absolutely calibrated large-scale emission to the Effelsberg data in both total and polarized intensity, much of the small-scale details are hidden in large-scale intensity gradients. We therefore separated the small and large-scale structures from each other using the "background filtering method" (Sofue & Reich 1979), which is based on an unsharp masking operation. This procedure has been applied to all absolutely calibrated total intensity maps. We separated emission on scales larger than about $3\hbox{$^\circ$}$ from compact sources and emission on smaller scales. The sum of both components is exactly the original intensity. This procedure and presentation of data has been already applied for the Effelsberg Galactic plane surveys at 1.4 GHz (Reich et al. 1990a, 1997), and 2.695 MHz (Reich et al. 1990b; Fürst et al. 1990).

  

Figure 1: Source counts from an area in the Galactic anticentre as described in Sect. 3

4.1 The area centered on $\ell = 50\hbox{$^\circ$},\ b = 12\hbox{$^\circ$}$

Figure 2 shows the small-scale total intensity emission with superimposed polarization vectors in E-field direction. Figure 3 shows the corresponding large-scale emission in total intensity and polarized intensities are shown in Fig. 4.

  

Figure 2: Small-scale total intensity image of the region towards $\ell = 50\hbox{$^\circ$}$ with superimposed polarization vectors in the E-field direction. Galactic coordinates are shown. The first contour set starts from 0 mK TB and runs in steps of 120 mK TB and the second contour set starts at 600 mK TB and runs in steps of 240 mK TB. The wedge at the top shows the lower and upper cuts of the image. Every second polarization vector is plotted and a vector of $2\hbox{$^\prime$}$ length corresponds to 100 mK TB in polarized intensity

  

Figure 3: Filtered large-scale total intensities of the area shown in Fig. 2. Contours start at 4500 mK TB and run in steps of 50 mK TB. The beam width of the filter was $3\hbox{$^\circ$}$

  

Figure 4: Polarized intensities of the area shown in Fig. 2. Contours start at 0 mK TB and run in steps of 60 mK TB. The wedge shows the lower and upper cuts of the image. This field is an example of a typical medium latitude region as the structured emission features decrease with increasing latitude

This field of $160~\ifmmode\hbox{\rlap{$\sqcap$}$\sqcup$}\else{\unskip\nobreak\hfil \penalty50... ...box{\rlap{$\sqcap$}$\sqcup$} \parfillskip=0pt\finalhyphendemerits=0\endgraf}\fi$ is located between the North Polar Spur to the west and the Cygnus-X region to the east, which both contain strong emission from local sources. The observed field seems less affected by local features and thus more representative for the medium latitude emission from the inner part of the Galaxy. The total intensity decreases smoothly with latitude (Fig. 3). Significant intensity variations in the small-scale total intensity up to $20\hbox{$^\circ$}$ latitude are visible in Fig. 2. The polarized intensities (Fig. 4) vary on small scales, but become more uniform for latitudes above $16\hbox{$^\circ$}$. A chain of high-velocity Hi-clouds extending from $\ell = 70\hbox{$^\circ$},\ b = 25\hbox{$^\circ$}$ towards the Galactic plane terminates close to $\ell = 52\hbox{$^\circ$},\ b = 10\hbox{$^\circ$}$, where enhanced synchrotron emission is visible as discussed by Uyaniker (1997).

4.2 The Cygnus superbubble

Figure 5 shows the small-scale emission of the southern and northern part of the Cygnus-X area in the same presentation as for Fig. 2. In Fig. 6 the corresponding large-scale total intensities are given and polarized intensities are shown in Fig. 7.

  

Figure 5: The left panel shows the small-scale total intensity map towards the northern part of the Cygnus region. The three contour sets start at 0 mK TB, 800 mK TB and 1800 mK TB (white contours) and run in steps of 150 mK TB, 300 mK TB and 750 mK TB, respectively. The right panel shows the total intensity map towards the southern part of the Cygnus region. The contours start at 0 mK TB and run in steps of 150 mK TB. The contours plotted in white start at 1200 mK TB and run in steps of 400 mK TB. In both of the panels the electric field vectors are scaled to the polarized intensity and 100 mK TB represented with a bar of length $8\hbox{$^\prime$}$. Every third vector is plotted

  

Figure 6: Large-scale total intensity map towards the northern part of the Cygnus region is shown in the upper panel. The first contour set starts at 4160 mK TB and runs in steps of 50 mK TB and the second contour set starts at 4800 mK TB and runs in steps of 300 mK TB. Cyg A at about $\ell \sim 76\hbox{$^\circ$}$ is blanked. The lower panel displays the large-scale total intensity map towards the southern part of the Cygnus region. The contour set starts at 4300 mK TB and runs in steps of 50 mK TB

  

Figure 7: The left panel shows the polarized intensity map towards the northern part of the Cygnus region. Contours start at 50 mK TB and run in steps of 50 mK TB. Cyg A at about $\ell \sim 76\hbox{$^\circ$}$ is blanked. Polarized intensity map towards the southern part of the Cygnus region is given in the right panel. Contours start at 30 mK TB and run in steps of 40 mK TB

The particular interest in this region arises from the large X-ray halo surrounding the Cygnus-X area, called the Cygnus superbubble (Cash et al. 1980). The Cygnus-X area is a quite strong and rather complex region in the radio range, since the line of sight is along the local spiral arm. No sensitive radio surveys of the area of the Cygnus superbubble exist so far and we will discuss the relation of the X-ray emission revealed by ROSAT during its all-sky survey with the 1.4 GHz radio emission in a forthcoming paper. Highly varying and strong polarized intensity is seen in some areas, where the total intensity images show rather smooth emission. In particular the regions centered around $\ell = 75\hbox{$^\circ$},\ b = -12\hbox{$^\circ$}$ south of the Cygnus loop ($\ell = 74\hbox{$^\circ$},\ b = -8\hbox{$^\circ$}$), the large emission feature almost filling the field of view and crossing the map diagonally and the structure at $\ell = 94\hbox{$^\circ$},\ b = -5\hbox{$^\circ$}$ about $3\hbox{$^\circ$}$ in size should be mentioned.

Some well-known polarized objects are visible. These are three supernova remnants: the Cygnus loop, HB21 ($\ell = 89\hbox{$^\circ$},\ b = 5\hbox{$^\circ$}$) and W63 ($\ell = 82\hbox{$^\circ$},\ b = 5\hbox{$.\!\!^\circ$}5$). At $\ell = 76\hbox{$^\circ$},\ b = 6\hbox{$^\circ$}$ the exceptionally strong emission from the radio galaxy Cygnus A shows up. Telescope sidelobes from the four support legs of the subreflector show up to about $4\hbox{$^\circ$}$ distance from the source in total intensity (Fig. 5) and slightly less in polarized intensity (Fig. 7).

4.3 The highly polarized region near $\ell = {\it 140}\hbox{$^\circ$}$

Figure 8 shows the area from $140\hbox{$^\circ$}\leq \ell \leq 153\hbox{$^\circ$}$ similar to Fig. 2, but polarization vectors represent the small-scale emission component. To separate the small-scale polarization structures, the strong sources are clipped in the absolutely calibrated U and Q maps and these maps are convolved to $3\hbox{$^\circ$}$. The convolved maps are subtracted from the original U and Q maps and the polarized intensity maps are prepared. Figure 9 is the corresponding large-scale emission in total intensity with superimposed polarization vectors from the large-scale component. Polarized intensities are shown in Fig. 10 (small-scale emission) and Fig. 11 (large-scale emission), respectively.

Early polarization surveys as reviewed by Salter & Brown (1988) already revealed an outstanding polarized region with more than $20\hbox{$^\circ$}$ in extent centered roughly at $\ell = 140\hbox{$^\circ$}$ and slightly north of the Galactic plane. Because of its morphology this area has been referred to as the "fan region". The polarized emission is believed to be of local origin. The derived Rotation measures are small (e.g. Bingham & Shakeshaft 1967) and the magnetic field direction has to be basically orientated perpendicular to the line of sight. However, in addition to the large-scale component, which we add from the Dwingeloo survey, a lot of small-scale variations are visible (Fig. 10).

  

Figure 8: Small-scale total intensity map close to $\ell ~\sim 140\hbox{$^\circ$}$. Contours start at 0 mK TB and run in steps of 100 mK TB. Small-scale polarization data are overlaid as vectors such that 100 mK TB corresponding to a bar of length $6\hbox{$^\prime$}$. Every second vector is plotted

  

Figure 9: Large-scale total intensity map near $\ell \sim 140\hbox{$^\circ$}$. Contours start at 4530 mK TB and run in steps of 10 mK TB. Large-scale electric field vectors are also overlaid. A vector whose length is $6\hbox{$^\prime$}$ corresponds to an intensity of 100 mK TB

  

Figure 10: Polarized intensity map of the small-scale emission near $\ell \sim 140\hbox{$^\circ$}$. Contours start at 0 mK TB and run in steps of 50 mK TB. This map partly covers the field from which the highest polarization emission in the Galaxy is observed

  

Figure 11: Large-scale polarized intensity map near $\ell \sim 140\hbox{$^\circ$}$. Contours start at 380 mK TB and run in steps of 15 mK TB

4.4 The anticentre region

Figures 12 to 14 display the results of the anticentre region north of the Galactic plane. Color images of the total intensity (Fig. 13) and polarization intensity in the direction of the Galactic anticentre show the polarization features and absence of corresponding total-power emission in detail. Although an absolute calibration of the polarized emission on large scales was not possible because of missing Dwingeloo data, significant small-scale polarization is found across the area. The most remarkable structures are apparently depolarized features (Fig. 13), which form filaments (e.g. at $\ell = 204\hbox{$^\circ$},\ b = 12\hbox{$^\circ$}$ or $\ell = 206\hbox{$^\circ$},\ b = 9\hbox{$^\circ$}$) or ring-like structures (e.g. at $\ell = 191\hbox{$^\circ$},\ b = 9\hbox{$^\circ$}$ or at $\ell = 196\hbox{$.\!\!^\circ$}5,\ b = 5\hbox{$.\!\!^\circ$}5$) with sizes up to about $3\hbox{$^\circ$}$. The depolarized features have no counterpart in the small-scale total intensity emission (Figs. 12,  13) or the large-scale component (Fig. 14). Depolarization can be caused either by some filamentary thermal matter with enhanced electron density, by magnetic field variations in strength and/or direction or the superposition of magnetic field components in the line of sight with orientations perpendicular to each other. Higher frequency observations with the 100-m telescope are underway to clarify the nature of these features.

  

Figure 12: Total intensity intensity map of the small-scale emission in the direction of the Galactic anticentre. Contours start at 0 mK TB and run in steps of 50 mK TB. Overlaid bars are electric field vectors such that 100 mK TB corresponds to $4\hbox{$^\prime$}$. Every second vector is plotted

  

Figure 13: Total intensity map of the small-scale emission (at top) and the polarized intensity map in the direction of the Galactic anticentre. Upper and lower cuts of the images are shown with a wedge

  

Figure 14: Large-scale total intensity map in the direction of the Galactic anticentre. Contours start at 3800 mK TB and run in steps of 25 mK TB