SOFIA/HAWC+ Far-Infrared Polarimetric Large Area CMZ Exploration Survey. I. General Results from the Pilot Program

Abstract

We present the first data release of the Far-Infrared Polarimetric Large Area CMZ Exploration (FIREPLACE) survey. The survey was taken using the 214 μm band of the HAWC+ instrument with the SOFIA telescope (19.″6 resolution; 0.7 pc). In this first data release we present dust polarization observations covering a ∼0.°5 region of the Galactic center’s central molecular zone (CMZ), approximately centered on the Sgr B2 complex. We detect ∼25,000 Nyquist-sampled polarization pseudovectors, after applying the standard SOFIA cuts for minimum signal-to-noise ratios in fractional polarization and total intensity of three and 200, respectively. Analysis of the magnetic field orientation suggests a bimodal distribution in the field direction. This bimodal distribution shows enhancements in the distribution of field directions for orientations parallel and perpendicular to the Galactic plane, which are suggestive of a CMZ magnetic field configuration with polodial and torodial components. Furthermore, a detailed analysis of individual clouds included in our survey (i.e., Sgr B2, Sgr B2-NW, Sgr B2-Halo, Sgr B1, and Cloud E/F) shows they have fractional polarization values of 1%–10% at 214 μm, with most of the emission having values <5%. A few of these clouds (i.e., Sgr B2 and Cloud E/F) show relatively low fractional polarization values toward their cores and higher fractional polarization values toward their less dense peripheries. We also observe higher fractional polarization toward compact H ii regions, which could indicate an enhancement in the grain alignment in the dust surrounding these sources.

SOFIA/HAWC+ Far-infrared Polarimetric Large Area CMZ Exploration Survey. II. Detection of a Magnetized Dust Ring in the Galactic Center

“…The magnetic field has an approximately circular structure (azimuthal orientation) that generally follows the curvature of the M0.8-0.2 ring. The bright 214 μm emission (i.e., I 214μm > 5000 MJy sr −1 ) has fractional polarization values of 1%-5%, comparable to those of other CMZ clouds in the FIREPLACE survey (Butterfield et al 2024). These fractional polarization values tend to increase toward the center of the circular structure (10%-20%; see Figure 3), suggesting grain alignment could be more efficient in this inner region.…”

“…The results presented in this paper utilize DR1 of a recent SOFIA/HAWC+ legacy survey of dust polarization in the CMZ: the SOFIA/HAWC+ FIREPLACE Survey (i.e., FIRE-PLACE I; see Butterfield et al 2024 for a full discussion of the reduction methods for the data shown in this paper). The FIREPLACE survey is a 214 μm study taken with the SOFIA telescope and HAWC+ polarimeter.…”

“…Therefore, the lower-intensity regions are potentially more influenced by unrelated background and foreground contributions. Analysis of the polarization pseudovectors in this lower-intensity regime was conducted for the FIREPLACE I survey (Butterfield et al 2024). They found a relatively uniform distribution of orientation angles for the field directions when compared with the higher-intensity regimes, indicating that there could be source confusion due to multiple field directions along the LOS in the higher-intensity regimes.…”

“…Figure 1, left, shows a three-color image of the eastern 125 pc (assuming a distance of 8.2 kpc to the Galactic center (GC); Gravity Collaboration et al 2019) of the CMZ (roughly the area covered by Data Release 1 (DR1) of the SOFIA/HAWC+ Far-Infrared Polarimetric Large Area CMZ Emission (FIRE-PLACE) survey, presented in Butterfield et al 2024), at 3 mm (green; Mustang Galactic Plane Survey (MGPS); Ginsburg et al 2020), 160 μm (red; Hi-GAL survey; Molinari et al 2016), and 8 μm (blue; GLIMPSE II survey; Churchwell et al 2009). In this figure the cool dust, highlighted in red, traces the dense molecular clouds; the green emission highlights the thermal bremsstrahlung (free-free; e.g., Sgr B2, Sickle), bright nonthermal synchrotron emission (e.g., Radio Arc), and cool dust; and the blue color represents polycyclic aromatic hydrocarbon emission caused by the UV emission from high-mass stars.…”

“…In this paper we present the detection of polarized 214 μm dust emission associated with the CMZ source M0.8-0.2 using data from the recent FIREPLACE survey (FIREPLACE I; Butterfield et al 2024). An overview of the FIREPLACE survey is discussed briefly in Section 2.…”