Magnetic Chaos Hidden in the Whirlpool Galaxy
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Alejandro Borlaff
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High resolution polarization observations of spiral galaxies in the far-infrared are enabling for the first time study of galactic magnetic fields deep into the cold dark molecular disks, where the most complex gas kinematics and star formation take place. Taking advantage of HAWC+, the far-infrared polarization imaging instrument installed in the Stratospheric Observatory for Infrared Astronomy (SOFIA), we study the polarized thermal emission of magnetically aligned dust grains at 154 um of the grand design spiral galaxy M51. We found significant differences between the spiral magnetic field of M51 traced with far-infrared and 3 cm and 6 cm radio continuum polarization observations. The outer structure of the far-infrared spiral magnetic field shows a significant distortion in the magnetic pitch angle profile which is not observable in the radio polarization maps, which are much more homogenous across the whole disk. Those distortions appear to be correlated with regions of higher specific star formation rate, not being observed in the interarm regions. This reveals a previously unknown and very complex scenario: radio observations trace a different magnetic field than far-infrared polarization observations. This is a consequence of the different locations of the ionized and molecular gas in the galactic disk, and the turbulent effects of star formation in the dense dust clouds. Multi-wavelength polarization observations are the key to disentangle the interlocked relation between star formation, magnetic fields and gas kinematics in the different phases of the interstellar medium.


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