J/A+A/622/A209 B2 0258+35 polarisation images (Adebahr+, 2019) ================================================================================ Polarised structures in the radio lobes of B2 0258+35. Evidence of magnetic draping? Adebahr B., Brienza M., Morganti R. =2019A&A...622A.209A (SIMBAD/NED BibCode) ================================================================================ ADC_Keywords: Galaxies, radio ; Polarization ; Magnetic fields Keywords: galaxies: magnetic fields - polarization - galaxies: jets - galaxies: active - galaxies: individual: NGC 1167 - galaxies: individual: B2 0258+35 Abstract: The contribution of active galactic nuclei to the magnetisation of the Universe can be constrained by knowing their duty cycles, jet and magnetic field morphologies, and the physical processes dominating their interaction with the surrounding environment. The magnetic field morphology and strength of radio lobes of AGN has an influence on the mechanisms for the propagation of cosmic rays into intergalactic space. Using the source B2 0258+35 we want to investigate the interaction of its radio lobes with the surrounding environment and examine the underlying physical effects. Published HI and radio continuum data at {lambda}21cm were combined with newly reduced archival Westerbork Radio Synthesis Telescope polarisation data at the same wavelength to investigate the polarised emission in the radio lobes of B2 0258+35. We assumed energy equipartition between the cosmic rays and the magnetic field to calculate their pressure and investigate the physical processes leading to the detected emission. We detected a unique S-shaped diffuse polarised structure. The lobes have a pressure of p=1.95+/-0.4x10^-14^dyn/cm^2^. The calculated total magnetic field strengths are low (B_eq_=1.21+/-0.12uG). We observe depolarisation in the northern lobe, which might originate from the HI-disc in the foreground. In addition we see an anti-correlation between the pressure and the fractional polarisation along the S-shaped structure. Therefore we consider magnetic draping and magnetic field compression as possible effects that might have created the observed S-shape. Our results suggest that magnetic draping can be effectively used to explain the observed polarised structures. This is likely due to the combination of a relatively low magnetic field strength, enabling super-Alfvenic motion of the rising lobes (with M_A_=2.47-3.50), and the coherency of the surrounding magnetic field. Moreover, the draped layer tends to suppress any mixing of the material between the radio lobes and the surrounding environment, but can enhance the mixing and re-acceleration efficiencies inside the lobes, providing an explanation for the average flat spectral index observed in the lobes. Description: The polarisation study presented in this paper is based on unpublished data of the radio galaxy B2 0258+35 from the WSRT archive. The data consist of two full 12 h tracks pointing at RA: 03:02:17.8, Dec: +35:14:36. The observations were undertaken between 4 and 6 November 2006. Each dataset was recorded over the full bandwidth of 160 MHz consisting of eight 20MHz sub-bands with 64 channels each and with centre frequencies equal to 1451, 1433, 1411, 1393, 1371, 1351, 1331, and 1311 MHz. All four linear correlations (XX, XY, YX, YY) were recorded, so that the data contained full polarisation information. Sources 3C48 and 3C147 were used as calibrators and were observed before and after the target field in each run, respectively. Objects: -------------------------------------------------- RA (2000) DE Designation(s) -------------------------------------------------- 03 01 42.36 +35 12 20.3 B2 0258+35 = NGC 1167 -------------------------------------------------- File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file list.dat 114 14 List of fits images fits/* . 14 Individual fits images -------------------------------------------------------------------------------- Byte-by-byte Description of file: list.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 9 F9.5 deg RAdeg Right Ascension of center (J2000) 10- 18 F9.5 deg DEdeg Declination of center (J2000) 20- 22 I3 --- Nx Number of pixels along X-axis 24- 26 I3 --- Ny Number of pixels along Y-axis 28- 48 A21 "datime" Obs.date Observaiton date 50- 53 I4 Kibyte size Size of FITS file 55- 77 A23 --- FileName Name of FITS file, in subdirectory fits 79-114 A36 --- Title Title of the FITS file -------------------------------------------------------------------------------- Acknowledgements: Bjorn Adebahr, adebahr(at)astro.rub.de ================================================================================ (End) Patricia Vannier [CDS] 26-Feb-2019