SOFIA/HAWC+ Far-Infrared Polarimetric Large-Area CMZ Exploration (FIREPLACE) Survey III: Full Survey Data Set

Abstract: We present the second data release (DR2) of the Far-Infrared Polarimetric Large-Area CMZ Exploration (FIREPLACE) survey. This survey utilized the Stratospheric Observatory for Infrared Astronomy (SOFIA) High-resolution Airborne Wideband Camera plus (HAWC+) instrument at 214 $\mu$m (E-band) to observe dust polarization throughout the Central Molecular Zone (CMZ) of the Milky Way. DR2 consists of observations that were obtained in 2022 covering the region of the CMZ extending roughly from the Brick to the Sgr C molecular clouds (corresponding to a roughly 1$^{\circ}$ $\times$ 0.75$^{\circ}$ region of the sky). We combine DR2 with the first FIREPLACE data release to obtain full coverage of the CMZ (a 1.5$^{\circ}$ $\times$0.75$^{\circ}$ region of the sky). After applying total and polarized intensity significance cuts on the full FIREPLACE data set we obtain $\rm\sim$65,000 Nyquist-sampled polarization pseudovectors. The distribution of polarization pseudovectors confirms a bimodal distribution in the CMZ magnetic field orientations, recovering field components that are oriented predominantly parallel or perpendicular to the Galactic plane. These magnetic field orientations indicate possible connections between the previously observed parallel and perpendicular distributions. We also inspect the magnetic fields toward a set of prominent CMZ molecular clouds (the Brick, Three Little Pigs, 50 km s$\rm^{-1}$, Circum-nuclear Disk, CO 0.02-0.02, 20 km s$\rm^{-1}$, and Sgr C), revealing spatially varying magnetic fields that generally trace the morphologies of the clouds. We find evidence that compression from stellar winds and shear from tidal forces are prominent mechanisms influencing the structure of the magnetic fields observed within the clouds.

• The paper presents the FIREPLACE DR2 survey’s novel 214 μm polarimetric mapping of the CMZ, capturing approximately 65,000 dust polarization pseudovectors.
• It employs advanced on-the-fly mapping techniques and CRUSH algorithm parameters to robustly separate astrophysical signals from correlated noise.
• The survey reveals bimodal magnetic field orientations relative to the Galactic plane, offering new insights into molecular cloud dynamics and star formation processes.

Overview of the SOFIA/HAWC+ Far-Infrared Polarimetric Large-Area CMZ Exploration (FIREPLACE) Survey III: Full Survey Data Set

The paper presents the second data release (DR2) of the FIREPLACE survey, conducted using SOFIA/HAWC+ at a wavelength of 214 μm (E-band) to map dust polarization within the Central Molecular Zone (CMZ) of the Milky Way. The DR2 covers observations conducted in 2022 and complements the first data release (DR1), achieving comprehensive polarimetric coverage of a 1.5° x 0.75° region of the CMZ. The survey successfully characterizes magnetic field structures within prominent molecular clouds, yielding roughly 65,000 Nyquist-sampled polarization pseudovectors. These vectors substantiate a bimodal magnetic field distribution, largely aligned parallel or perpendicular to the Galactic plane, suggesting potential interactions between distinct magnetic field orientations within the CMZ.

Key Observations and Methodology

The CMZ's magnetic field was examined with unprecedented resolution at far-infrared frequencies. Utilizing the novel on-the-fly mapping (OTFMAP) mode on SOFIA/HAWC+, the survey overcame challenges posed by the CMZ’s substantial spatial extent and complex emission structures. Data reduction involved advanced parameters in the CRUSH algorithm, ensuring effective differentiation of correlated noise from genuine astrophysical signals. The resulting observations elucidate the CMZ’s magnetic field geometries, crucially linking local molecular cloud structures to broader galactic dynamics.

Insights into Magnetic Field Configuration

The survey identifies a critical distinction in magnetic field orientations across different intensity regimes within the CMZ:

• High Intensity Regimes: Magnetic fields correlate with cloud structures, oriented parallel to molecular cloud morphologies. This is notably evident in the Brick and Three Little Pigs clouds, where the magnetic field likely responds to gravitational and compressive forces internal to these clouds.
• Middle and Low Intensity Regimes: Enhanced bimodal polarization distributions suggest a mix of local field alignment and potential large-scale magnetic field contributions from the Galactic center. The coherent vertical field components in these regions might connect with non-thermal filament structures observed in radio frequencies.

Implications and Prospective Research Directions

The FIREPLACE survey's high-resolution polarimetric mapping of the CMZ provides pivotal insights into the interplay between magnetic fields, molecular cloud dynamics, and star formation processes. It facilitates a nuanced understanding of how large-scale and local magnetic fields cooperate or oppose each other within such a complex galactic environment. These findings can be instrumental in refining models of magnetic field evolution, cloud collapse, and star formation in extreme environments.

Future investigations could leverage this comprehensive polarimetric dataset to develop predictive models of magnetic field influence on molecular cloud stability and star formation. Additionally, cross-referencing these observations with data from other wavelengths—such as radio synchrotron emissions—could extend understanding of magnetic field interactions across multiple scales.

In conclusion, the FIREPLACE survey epitomizes a critical advancement in the study of Galactic center magnetic fields, showcasing the significant role of polarimetric data in unraveling the complexities of the Milky Way’s inner regions. Further refinement of magnetic field models based on these findings will enhance the comprehensive understanding of galactic dynamics and star formation processes.