Extragalactic Magnetism with SOFIA (SALSA Legacy Program). V. First Results on the Magnetic Field Orientation of Galaxies
Abstract
We present the analysis of the magnetic field (B-field) structure of galaxies measured with far-infrared (FIR) and radio (3 and 6 cm) polarimetric observations. We use the first data release of the Survey of extragALactic magnetiSm with SOFIA of 14 nearby ( $\lt 20$ Mpc) galaxies with resolved ( $5^{\prime\prime} \mbox{--}18^{\prime\prime} ;$ 90 pc-1 kpc) imaging polarimetric observations using SOFIA/HAWC+ from 53 to 214 μm. We compute the magnetic pitch-angle ( ${{\rm{\Psi }}}_{B}$ ) profiles as a function of the galactocentric radius. We introduce a new magnetic alignment parameter (ζ) to estimate the disordered-to-ordered ratio of spiral B-fields. We find FIR and radio wavelengths to not generally trace the same B-field morphology in galaxies. The ${{\rm{\Psi }}}_{B}$ profiles tend to be more ordered across all galactocentric radii in radio ( ${\zeta }_{6\mathrm{cm}}\,=\,0.93\pm 0.03$ ) than in FIR ( ${\zeta }_{154\mu {\rm{m}}}=0.84\pm 0.14$ ). For spiral galaxies, FIR B-fields are 2%-75% more turbulent than the radio B-fields. For starburst galaxies, we find that FIR polarization is a better tracer of the B-fields along the galactic outflows than radio polarization. Our results suggest that the B-fields associated with dense, dusty, turbulent star-forming regions (those traced at FIR) are less ordered than warmer, less dense regions (those traced at radio) of the interstellar medium. The FIR B-fields seem to be more sensitive to the activity of the star-forming regions and molecular clouds within a vertical height of a few hundred parsecs in the disk of spiral galaxies than the radio B-fields.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 2023
- DOI:
- 10.3847/1538-4357/acd934
- arXiv:
- arXiv:2303.13586
- Bibcode:
- 2023ApJ...952....4B
- Keywords:
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- Astrophysical magnetism;
- Extragalactic magnetic fields;
- Polarimetry;
- Dust continuum emission;
- Radio continuum emission;
- Galaxy evolution;
- Spiral galaxies;
- Disk galaxies;
- 102;
- 507;
- 1278;
- 412;
- 1340;
- 594;
- 1560;
- 391;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - Instrumentation and Methods for Astrophysics
- E-Print:
- 28 pages, 14 figures. Accepted for publication in The Astrophysical Journal