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Astron. Astrophys. 345, 461-470 (1999)

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Magnetic fields and strong density waves in the interacting galaxy NGC 3627

M. Soida 1, M. Urbanik 1, R. Beck 2 and R. Wielebinski 2

1 Astronomical Observatory, Jagiellonian University, Kraków, Poland
2 Max-Planck-Institut für Radioastronomie, Postfach 2024, D-53010 Bonn, Germany

Received 18 September 1998 / Accepted 8 February 1999


We present 10.55 GHz observations of the strong-density-wave spiral NGC 3627. Total power and polarization maps with a resolution of 1[FORMULA] 13, sensitive to a weak extended emission were obtained. In the analysis we used also available data in the CO and H[FORMULA] lines.

The total power brightness distribution shows two equally bright sources close to the bar ends, coincident with similar peaks in CO and H[FORMULA]. The strong central peak of the CO emission does not correspond to a detectable central source in radio continuum. A weak H[FORMULA] flux from this region is thus due not only to a strong absorption but may also indicate a low star formation level in the central molecular complex. The equally strong total power peaks at the bar ends do not reflect the asymmetry of the H[FORMULA] emission, the latter being stronger at the northern bar end. The H[FORMULA] asymmetry is likely to be due to differences in absorption.

The polarized emission has the form of two asymmetric lobes with B-vectors running parallel to the optical arms. The stronger lobe is located at the position of the dust lane in the western arm while the weaker one falls on the middle of the interarm space in the NE disk. Smooth polarized emission away from any spiral structures was also detected. Despite the strong density waves, many polarization properties of this galaxy like the large-scale distribution of polarized intensity or azimuthal variations of magnetic pitch angles can be reasonably explained by the presence of an axisymmetric, dynamo-type magnetic field component. However, extra effects like the depolarization of the southern segment of the eastern arm by vertical fields above star-forming regions, as well as some compressional enhancement of regular fields in the western arm seem necessary to explain our polarization data.

Key words: polarization – galaxies: individual: NGC 3627 – galaxies: magnetic fields – galaxies: spiral – radio continuum: galaxies

Send offprint requests to: M. Urbanik

Correspondence to: urb@oa.uj.edu.pl

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© European Southern Observatory (ESO) 1999

Online publication: April 19, 1999