Interstellar polarization at high galactic latitudes from distant stars III. Distribution of the polarization vectors – evidence for distinct zones

We make a map of interstellar polarization direction around the North Galactic Pole and study the distribution of the revealed magnetic field lines. We study in detail Markkanen’s (1979) cloud and other local features apparent in the polarization map, and compare them with the IRAS 100 micron map. The elongated Markkanen’s cloud (at a distance of 100–200 pc) and its magnetic field lines coincide with IRAS filaments. The cloud throws a shadow in soft (0.25 keV ROSAT) X-rays, as expected from its close distance. Another interesting feature is the polarization alignment around l ≈ 190◦, b ≈ 75◦ − 83◦, with the direction about perpendicular to that of Markkanen’s cloud, hence also perpendicular to the Local Spiral spur. This feature is shown only by stars more distant than 300 pc, and in the IRAS map it is located in a region of enhanced brightness. The differing polarization directions partially overlap in the sky, suggesting the existence of two kinds of clouds with different magnetic field directions. The IRAS 100 micron map is faint towards the sector 40◦ < l < 135◦. Only in this region with little nearby diffuse matter is there some signature of the global magnetic field (parallel with l ≈ 78◦).