CHIMPS2: the physical properties and star formation efficiency of molecular gas in the central molecular zone

King, SM, Moore, TJT, Longmore, SN ORCID: 0000-0001-6353-0170, Eden, DJ, Henshaw, JD ORCID: 0000-0001-9656-7682, Rigby, AJ and Rani, R (2026) CHIMPS2: the physical properties and star formation efficiency of molecular gas in the central molecular zone. Monthly Notices of the Royal Astronomical Society, 546 (4). ISSN 0035-8711

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Abstract

We present Local Thermodynamic Equilibrium estimates of the physical properties and star formation efficiency (SFE) of molecular gas in the central molecular zone (CMZ), using new 12 CO J = 2 → 1 observations from the James Clerk Maxwell Telescope. Combined with 12 CO and 13 CO J = 3 → 2 data from the CO Heterodyne Inner Milky Way Plane Survey 2 (CHIMPS2), and 13 CO J = 2 → 1 data from the Structure, Ex citation and Dynamics of the Inner Galactic Interstellar Medium (SEDIGISM), we estimate a median e x citation temperature of T ex = 11 K for 13 C O throughout the CMZ, with peaks exceeding 120 K in the Sgr B1/B2 complex. Cooler g as dominates around Sgr A and nearby clouds. We derive a median H 2 column density of N(H2) = 2 ×10 22 cm −2 and a total 13 CO-traced gas mass of M gas = 7 ×106 M , consistent with previous estimates when accounting for spatial coverage. The instantaneous SFE is assessed using Hi-GAL compact sources detected at 70 μm and 160–500 μm . The 70- μm -bright SFE, tracing current star formation, is modest overall but elevated in Sgr B1/B2, the Arches cluster, and Sgr C. In contrast, the 160–500 μm SFE, tracing cold pr e-stellar g as, is mor e broadly enhanced, particularly in the dust ridge clouds and towards negative longitudes surrounding Sgr C. The contrasting distributions suggest an evolutionary gradient in SFE, consistent with a transition from dense, cold gas to embedded protostars. Our results imply that the CMZ may enter a mor e active phase of star formation, with large reservoirs of gas

Item Type:	Article
Uncontrolled Keywords:	stars: formation; ISM: molecules; ISM: structure; Galaxy: centre; 5109 Space Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; 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:	Oxford University Press
Date of acceptance:	5 February 2026
Date of first compliant Open Access:	22 April 2026
Date Deposited:	22 Apr 2026 12:54
Last Modified:	22 Apr 2026 12:54
DOI or ID number:	10.1093/mnras/stag249
URI:	https://researchonline.ljmu.ac.uk/id/eprint/28429

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