SOFIA/HAWC+ traces the magnetic fields in NGC 1068 (1907.06648v2)

Abstract: We report the first detection of galactic spiral structure by means of thermal emission from magnetically aligned dust grains. Our 89 $\mu$m polarimetric imaging of NGC 1068 with the High-resolution Airborne Wideband Camera/Polarimeter (HAWC+) on NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA) also sheds light on magnetic field structure in the vicinity of the galaxy's inner-bar and active galactic nucleus (AGN). We find correlations between the 89 $\mu$m magnetic field vectors and other tracers of spiral arms, and a symmetric polarization pattern as a function of the azimuthal angle arising from the projection and inclination of the disk field component in the plane of the sky. The observations can be fit with a logarithmic spiral model with pitch angle of $16.9^{+2.7}_{-2.8}$$^{\circ}$ and a disk inclination of $48\pm2^{\circ}$. We infer that the bulk of the interstellar medium from which the polarized dust emission originates is threaded by a magnetic field that closely follows the spiral arms. Inside the central starburst disk ($<1.6$ kpc), the degree of polarization is found to be lower than for far-infrared sources in the Milky Way, and has minima at the locations of most intense star formation near the outer ends of the inner-bar. Inside the starburst ring, the field direction deviates from the model, becoming more radial along the leading edges of the inner-bar. The polarized flux and dust temperature peak $\sim 3-6$" NE of the AGN at the location of a bow shock between the AGN outflow and the surrounding interstellar medium, but the AGN itself is weakly polarized ($< 1$%) at both 53 and 89 \um.

• The paper uses far-infrared polarimetry with SOFIA/HAWC+ to detect and model the spiral magnetic field structure in NGC 1068.
• It finds that regions of intense star formation in the inner bar exhibit lower polarization, indicating more turbulent magnetic conditions.
• The study reveals weak AGN polarization with a dust temperature peak, suggesting interactions such as bow shocks from AGN outflows.

Analysis of Magnetic Fields in the Spiral Galaxy NGC 1068 Using SOFIA/HAWC+ Observations

The paper "SOFIA/HAWC+ traces the magnetic fields in NGC 1068" by Lopez-Rodriguez et al. provides a novel investigation into the magnetic fields of the nearby spiral galaxy NGC 1068. Utilizing the High-resolution Airborne Wideband Camera/Polarimeter (HAWC+) aboard NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA), the authors have reported the first detection of spiral magnetic structure in a galaxy through thermal emission from magnetically aligned dust grains. The focus of the paper was on the nuclear and bar regions of NGC 1068, a Seyfert 2 galaxy with significant starburst activity and a luminous active galactic nucleus (AGN).

Main Findings

1. Magnetic Field Structure: The linear polarization at 89 $\mu$m reveals a prominent spiral magnetic field structure that aligns with the observed spiral arms of NGC 1068. This paper models a logarithmic spiral with a pitch angle of approximately 16.9 degrees and finds the magnetic field closely follows the galactic disk's inclination of about 48 degrees.
2. Inner-Bar Region: Within the central starburst disk, polarization is notably lower when compared to the far-infrared sources within the Milky Way, reaching minimum values in regions of intense star formation near the ends of the inner-bar. This suggests that magnetic fields are more turbulent in such high-star formation zones.
3. AGN Proximity: The AGN itself exhibits weak polarization below 1% at both 53 and 89 $\mu$m, although the polarized flux and dust temperature peak northeast of the AGN, indicating potential interactions such as a bow shock created by AGN outflows.
4. Comparative Methods: The paper demonstrates the efficacy of far-infrared polarimetry as a complementary tool to optical and radio methods for tracing magnetic fields, particularly in high-opacity environments not accessible through other techniques.

Implications and Future Directions

This research offers substantial insight into the interplay between magnetic fields and the large-scale structure of spiral galaxies. Understanding the correlation between the magnetic field lines and the spiral arms can provide clues about the dynamical processes governing galaxy formation and evolution. NGC 1068 serves as an exemplary case due to its pronounced AGN activity and starburst regions, which are areas of focus for future studies aimed at bridging small and large-scale astrophysical phenomena.

Future developments in this area could include high-resolution simulations and further observational campaigns using advanced infrared polarimeters. These efforts would aim to discern the effects of environmental factors such as shocks from AGN outflows on magnetic field morphology. Additionally, addressing limitations in spatial resolution can help refine our understanding of the interaction between magnetic fields and star-forming regions in spiral galaxies.

In conclusion, the findings by Lopez-Rodriguez et al. significantly contribute to the field of galactic magnetic fields and open avenues for new research that could shed light on the underlying principles of spiral galaxy dynamics and their magnetic interdependencies.