Cara Battersby

We present data from the ALMA Central Molecular Zone Exploration Survey (ACES) Large Program, which provides broad spectral-line and 3 mm continuum coverage of the Central Molecular Zone (CMZ) at a spatial resolution of 0.1 pc. The survey delivers homogeneous, wide-field mosaics that enable direct comparisons of the physical and chemical conditions across diverse environments in the Galactic centre. In this data release paper, we present the CS($2-1$), SO(2$_{3}-1_{2}$), CH$_3$CHO($5_{1,4}-4_{1,3}$), HC$_3$N($11-10$), and H40$\alpha$ lines observed simultaneously within two broad spectral windows. These lines reveal pronounced spatial and chemical variations across the CMZ, tracing distinct components of molecular gas, shock-affected regions, and ionized structures. The high angular resolution and multi-line capability of the ACES data set make it a powerful resource for future studies of gas dynamics, star formation activity, and the physical connection between the CMZ and Sgr A*.

The central molecular zone (CMZ) resides in the inner few hundred parsecs of our Galaxy, and despite being the largest reservoir of dense molecular gas in the Milky Way, it has a relatively low present-day star formation rate (SFR) of ∼0.08 M _⊙ yr ⁻¹ . Continuum and spectral line observations from the Atacama Large Millimeter/submillimeter Array (ALMA) CMZ Exploration Survey (ACES) provide the first full-coverage, high-resolution map of the inner 200 pc of the CMZ at 3 mm. In this paper we present the ACES catalog of compact continuum sources, the most complete catalog of potential sites of star formation in the CMZ to date. Using an automated dendrogram-based source extraction procedure in combination with a by-eye morphological classification scheme, we produce a “full” catalog of 1735 detections in total. Additionally, we use spectral index measurements to generate a “filtered” catalog of 567 sources with minimal contamination from nonthermal filaments and extended free–free emission. We find that 359 (∼63%) of the filtered catalog sources are located at column densities 23 cm ⁻² , outside of the densest molecular cloud regions, 195 of which have not been identified in previous surveys. After cross-referencing with various catalogs generated from data at different wavelengths, we consider it likely that many of these newly discovered detections are produced by pre-/protostellar sources or compact H ii regions.

Context . High-mass star-forming regions are rich in complex organic molecules (COMs), which are carbon-bearing species with at least six atoms. Their formation pathways remain debated. The ALMA evolutionary study of high-mass protocluster formation in the GALaxy (ALMAGAL) survey provides a unique opportunity to probe this chemical complexity in a large statistical significant sample of high-mass star-forming regions. Aims . We present a detailed molecular line analysis of one of the most chemically rich cores in the ALMAGAL sample, the high-mass core 9 in the AG318.9477−00.1960 clump (AG318−c9), located at a heliocentric distance of ∼10.4 kpc. This source was selected because it combines an exceptionally high line density with a relatively simple kinematic structure, making it an optimal template for chemical analysis in the survey. We further assessed whether the emission of selected COMs, that is, ethylene glycol ((CH ₂ OH) ₂ ; EG), glycolaldehyde (CH ₂ (OH)CHO; GA), and methyl formate (CH ₃ OCHO; MF), can be used to trace the innermost regions of hot molecular cores (HMCs). Methods . We analysed ALMA Band 6 observations (∼217–221 GHz). Spectral line identification and local thermodynamic equilibrium modelling were performed using the software called MAdrid Data CUBe Analysis (MADCUBA). We derived the physical parameters, including the column density ( N ), excitation temperature ( T _ex ), velocity, line width, and molecular abundances relative to H ₂ , for all detected species. The chemical inventory of AG318−c9 was compared with that of the HMC G31.41 + 0.31 (G31). In addition, we performed a pixel-by-pixel analysis of EG, GA, and MF to generate spatially resolved N and T _ex maps and corresponding radial profiles. Results . We report the detection of 65 molecular species, including 31 main species and 34 isotopologues and vibrationally excited species. Of these, 44 are O-bearing species, 28 are N-bearing, 8 are S-bearing, and 2 are Si-bearing. While AG318−c9 exhibits lower abundances than G31 overall, it shows detections of species that have not yet been reported in G31, such as ethyl formate (C ₂ H ₅ OCHO). Moreover, 12 species depart from the general trend, displaying relative overabundances in AG318−c9. The comparison also reveals a chemical differentiation between O- and N- bearing COMs, with O-bearing species systematically more abundant in G31. Regarding EG, GA, and MF, the latter is the most abundant ( X ∼ 3 × 10 ⁻⁸ ), followed by EG ( X ∼ 7 × 10 ⁻⁹ ) and GA ( X ∼ 2 × 10 ⁻⁹ ). The N and T _ex maps suggest that MF is the most spatially extended species, whereas EG and GA are more compact and confined to the innermost hot region. Conclusions . AG318−c9 reveals a rich chemical inventory characteristic of an HMC. The chemical comparison with G31 suggests that AG318−c9 is a less evolved hot core dominated by the recent sublimation of ice mantles, in contrast to the higher abundances observed in the possible more evolved G31. MF emerges as an excellent tracer of the gas temperature in HMCs owing to its wide spatial extent and wide dynamic range of the excitation temperature. In contrast, EG and GA are more compact and preferentially trace the innermost high-density regions of the core, suggesting a high sublimation temperature threshold and supporting a shared grain-surface formation pathway. While EG and MF seem to be partly limited by sensitivity, GA reflects an intrinsically central distribution.

The Central Molecular Zone (CMZ) is an extreme star formation environment, characterized by higher density, higher turbulence, stronger orbital shear, and stronger magnetic field strength than the solar neighborhood. It is still debated whether classical theories of star formation hold within this extreme environment. In order to assess the impact of these different conditions on the interstellar medium (ISM) and on star formation, we present radiation magnetohydrodynamic AREPO simulations of a Milky Way-type galaxy. We set up a high-resolution ( M _cell = 20 M _⊙ ) region in a ring around the solar radius and in the barred region of the Galaxy to have a coherent comparison between the CMZ and the solar neighborhood. Although the high densities and strong levels of turbulence affect star formation and feedback, a key difference in the regulation of star formation between the two environments comes from the short orbital times and the strong shear in the CMZ. In particular, we highlight the role of the quick dynamical decoupling of stars and gas, which leads to periodic re-embedding events in the early lifetimes of radiating O stars. Young stellar associations are efficiently sheared apart, such that the ISM is deprived of the compounding effect of radiation and supernovae in disrupting molecular clouds. This dramatically changes the evolution of giant molecular clouds and how feedback can regulate star formation in the CMZ. Stellar feedback is no longer directly coupled to the molecular cloud from which they formed, and no strong and disruptive superbubbles can develop. The feedback instead rather acts as a background source of turbulence.

We employ a minimum spanning tree approach to characterize the spatial distribution and mass segregation of compact millimeter continuum sources within the Central Molecular Zone (CMZ) of the Milky Way. We use a modified form of the complete version of the 1.3 mm dust continuum catalog from the CMZoom survey, which identifies 685 compact sources with typical effective radii of ∼0.1 pc. For 22 of 35 CMZ clouds, we calculate the thermal and turbulent Jeans lengths and masses, and determine that compact source separations, as well as compact source masses, are more consistent with thermal fragmentation at ∼0.1 pc size scales. We construct the mass segregation ratios for compact sources in 17 CMZ clouds and determine that five of the analyzed clouds display some form of mass segregation (Λ _MSR > 1.5), while the remaining clouds show either inverse mass segregation (Λ _MSR < 0.75), or no evidence of true mass segregation (0.75 < Λ _MSR < 1.5). Finally, we find that although some actively star-forming clouds do exhibit mass segregation, other similarly active clouds do not, indicating an unclear correlation with evolutionary stage for star forming clouds in the CMZ, given the current available data.