ACES: The Magnetic Field in Large Filaments in the Galactic Center

TL;DR

This paper tackles how magnetic fields influence the formation and support of dense filaments in the Galactic Center's Central Molecular Zone (CMZ). It identifies large HNCO filaments in ALMA ACES data and measures their magnetic-field orientation using 214 μm polarimetry from SOFIA/HAWC+ and 850 μm polarimetry from JCMT/BISTRO, comparing to MHD-model predictions. The results indicate a range of local conditions, with some filaments in turbulence-dominated regimes and others in magnetically dominated regimes that resist collapse. The CMZ filaments appear analogous to the Galactic-disk 'bones,' suggesting a shared mechanism for forming magnetized, dense filaments across different Galactic environments.

Abstract

The Galactic Center (GC) is an extreme region of the Milky Way that is host to a complex set of thermal and non-thermal structures. In particular, the GC contains high-density gas and dust that is collectively referred to as the Central Molecular Zone (CMZ). In this work, we study a subset of HNCO filaments identified in band 3 ALMA observations of the GC obtained by the ALMA CMZ Exploration Survey (ACES) that are comparable to high density filaments identified in the Galactic Disk. We compare the orientation of the magnetic field derived from 214 um SOFIA and 850 um JCMT observations with the filament orientation to determine which mechanisms dominate the formation of these filaments. We observe a large range of magnetic orientations in our observed filaments indicating the complex environments the filaments are located in. We also compare the observational results to synthetic data sets created using an MHD model of the GC. Our analysis reveals that the dominant mechanisms local to the HNCO filaments vary throughout the GC with some filaments being dominated by supersonic turbulence and others by subsonic turbulence. The comparison to synthetic observations indicates that the observed filaments are in magnetically dominated environments that could be supporting these filaments against collapse. Our results on the CMZ filaments are also compared to results obtained on similar filaments located in the Galactic Disk, and we find that the filaments studied here are possible CMZ analogs to the dense filamentary "bones" observed previously in the Galactic Disk.

Figures (3)

• Figure 1: A 3-color view of the GC with 20 cm (1.28 GHz) MeerKAT radio emission tracing hot plasma in yellow Heywood2022, 250 $\mu$m cool dust observed by Herschel in cyan Molinari2011, and the 3.4 mm (87.9 GHz) ACES HNCO 4-3 moment 0 distribution observed in ALMA band 3 in purple (Longmore et al. submitted; Walker et al. submitted).
• Figure 2: The ACES HNCO moment 0 distribution (Longmore et al. submitted) saturated to show the fainter filamentary features in the CMZ. FIREPLACE 214 $\mu$m and BISTRO 850 $\mu$m magnetic field orientations are overlaid as blue and yellow dashes, respectively Pare2024karoly25. The CMZ cloud regions and northern extent of the ACES coverage that have been masked out are indicated with red boxes.
• Figure 3: The final RHT distribution used to identify filamentary structures in the ACES HNCO distribution. We show the RHT distribution obtained from the HNCO distribution that has been convolved to the 19.6$^{\prime\prime}$ FIREPLACE beam size. The black contour traces the cool dust traced by the FIREPLACE 214 $\mu$m observations at a level of 6 Jy pixel$^{-1}$ and indicates the CMZ molecular clouds that have been masked out. The boxes indicate the locations of the filaments that are targeted for a detailed analysis in this work. Blue boxes indicate filaments that coincide with only FIREPLACE magnetic field orientations and green boxes indicate filaments that coincide with both FIREPLACE and BISTRO magnetic field orientations. In addition, red and orange boxes indicate the filaments previously studied in Battersby et al. (submitted) where the red boxes coincide with only FIREPLACE magnetic field orientations and the orange box coincides with both FIREPLACE and BISTRO magnetic field orientations. The filaments studied within each of these regions are shown in Figures \ref{['fig:hro_rht_sofia_fig1']} and \ref{['fig:hro_rht_sofia_fig2']}.