Astron. Astrophys. 358, 717-722 (2000)

Interstellar polarization at high galactic latitudes from distant stars

III. Distribution of the polarization vectors - evidence for distinct zones

A. Berdyugin ^1,2,3, P. Teerikorpi ¹ and L. Haikala <sup>4,5

1</sup> Tuorla Observatory, 21500 Piikkiö, Finland (andrei,pekkatee@deneb.astro.utu.fi)
² Crimean Astrophysical Observatory, 334413 Nauchny, Crimea, Ukraina
³ Astronomy Division, University of Oulu, Linnanmaa, PL 3000, 90401 Oulu, Finland
⁴ European Southern Observatory, Casilla 19001, Santiago, Chile (lhaikala@eso.org)
⁵ Observatory and Astrophysics Laboratory, P.O. Box 14 00014, Helsinki University, Finland

Received 25 January 2000 / Accepted 21 March 2000

Abstract

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 , 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 . Only in this region with little nearby diffuse matter is there some signature of the global magnetic field (parallel with ).

Key words: polarization ISM: dust, extinction Galaxy: solar neighbourhood

Send offprint requests to: A. Berdyugin

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Contents

• 1. Introduction
• 2. The sample of stars and data
• 3. The map of the polarization direction
  • 3.1. Polarization map
  • 3.2. Distribution of position angle
• 4. Background for interpretation: local and global Galactic structure
  • 4.1. Local Spiral spur at high latitudes
  • 4.2. Global magnetic field
• 5. Revisiting Markkanen's cloud
• 6. What happens around ?
• 7. Comparison with the IRAS map
• 8. Discussion and conclusions
  • 8.1. The soft X-ray shadow of Markkanen's cloud
  • 8.2. Different field directions
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: June 8, 2000
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