ALMA Central Molecular Zone Exploration Survey (ACES) – VI. ALMA large program reveals a highly filamentary Central Molecular Zone

ABSTRACT The Central Molecular Zone (CMZ) of the Milky Way is the way station that primarily controls how much gas flows from the disc of the Galaxy towards the central nucleus. While this region is well documented to have extreme gas properties that clearly distinguish it from the rest of the Galaxy, the properties of the bulk molecular gas at high angular resolution are relatively unexplored. Band 3 data from the ALMA (Atacama Large Millimeter/Submillimeter Array) large program ACES (ALMA CMZ Exploration Survey) reveal the highly filamentary nature of CMZ molecular gas at high resolution (3 arcsec or $\sim$0.1 pc) across the entire CMZ. Visual inspection of these data suggests that there are at least two general classes of elongated structures, which we identify as: (i) large-scale ($\gtrsim 10$ pc) filamentary structures (LFs) and (ii) a ubiquitous population of small-scale ($\sim 1$ pc) filamentary structures (SFs), both with widths (FWHM) of about 0.1 pc. We present detailed morphological and kinematic properties towards three structures in each category, as well as their association with magnetic fields and the correlation of HNCO 4(0,4)–3(0,3) with other molecular species. Our investigation reveals that these structures are largely coherent in position–position–velocity space. The alignment with the magnetic field structure is mixed, with some parallel, some perpendicular, and some intermediate alignments. We find that LFs likely trace pieces of contiguous CMZ orbital structures and are a manifestation of global CMZ dynamics. The second class, SFs, are pervasive and may be the result of complicated turbulence and shearing dynamics in the CMZ gas flows, as seen in numerical simulations.