Magnetic field in the central region of the Circinus galaxy with SOFIA/HAWC+

Magnetic fields are known to play a key role in the structure and evolution of galaxies. Magnetic fields can be studied through polarimetric observations, from radio to optical wavelengths, however these wavelengths are affected by scattering and Faraday rotation, respectively. We present the first polarimetric observations of the central 1kpc region of the Circinus galaxy (D ≈ 4.2 Mpc) in the far-infrared range 53-214 μm, using data from the High-resolution Airborne Wideband Camera/Polarimeter-Plus (HAWC+) on NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA). These observations trace the magnetic fields by means of polarized emission from magnetically aligned dust grains. The active nucleus is found to be unpolarized and the absence of deviation of the polarization pattern at its location bring new upper constraints to the active nucleus polarized flux in the far-infrared. Our FIR polarization also traces the flows of matter in the inner-bar of the galaxy. An axisymmetrical spiral-like magnetic field model reproduces the observed polarization degree and position angle at 20” (≈ 400 pc) from the center with an inclination of ~80 degrees on the line of sight and with a position angle of -55 degrees East from North. Finally, these observations allow us to estimate the grain alignment efficiency as a function of the H column density and temperature of the ISM in the inner-bar of the galaxy.