3D CMZ. II. Hierarchical Structure Analysis of the Central Molecular Zone

Battersby, C, Walker, DL, Barnes, A, Ginsburg, A, Lipman, D, Alboslani, D, Hatchfield, HP, Bally, J, Glover, SCO, Henshaw, JD, Immer, K, Klessen, RS, Longmore, SN, Mills, EAC, Molinari, S, Smith, R, Sormani, MC, Tress, RG and Zhang, Q (2025) 3D CMZ. II. Hierarchical Structure Analysis of the Central Molecular Zone. The Astrophysical Journal, 984 (2). pp. 1-24. ISSN 0004-637X

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Abstract

The Central Molecular Zone (CMZ) is the way station at the heart of our Milky Way Galaxy, connecting gas flowing in from Galactic scales with the central nucleus. Key open questions remain about its 3D structure, star formation properties, and role in regulating this gas inflow. In this work, we identify a hierarchy of discrete structures in the CMZ using column density maps from Paper I (C. Battersby et al.) We calculate the physical (N(H2), Tdust, mass, radius) and kinematic (HNCO, HCN, and HC3N moments) properties of each structure as well as their bolometric luminosities and star formation rates. We compare these properties with regions in the Milky Way disk and external galaxies. Despite the fact that the CMZ overall is well below the Gao-Solomon dense gas star formation relation (and in modest agreement with the Schmidt–Kennicutt relation), individual structures on the scale of molecular clouds generally follow these star formation relations and agree well with other Milky Way and extragalactic regions. We find that individual CMZ structures require a large external pressure (Pe/kB > 107−9 K cm−3) to be considered bound; however, simple estimates suggest that most CMZ molecular-cloud-sized structures are consistent with being in pressure-bounded virial equilibrium. We perform power-law fits to the column density probability distribution functions of the inner 100 pc, SgrB2, and the outer 100 pc of the CMZ as well as several individual molecular cloud structures and find generally steeper power-law slopes (−9 < α < −2) compared with the literature (−6 < α < −1).

Item Type:	Article
Uncontrolled Keywords:	5101 Astronomical Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics; 0306 Physical Chemistry (incl. Structural); Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	American Astronomical Society
Date of acceptance:	2 December 2024
Date of first compliant Open Access:	15 May 2025
Date Deposited:	15 May 2025 12:55
Last Modified:	15 May 2025 13:15
DOI or ID number:	10.3847/1538-4357/adb844
URI:	https://researchonline.ljmu.ac.uk/id/eprint/26365

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