Ashley Thomas Barnes

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.

We present the largest study to date of star cluster mass and age distributions in nearby galaxies. The analysis is based on a uniformly selected catalog of over 15,000 (36,000) human- (machine-) classified compact clusters across 38 spiral galaxies in the PHANGS-Hubble Space Telescope survey, with improved photometric SED age dating that mitigates key degeneracies with reddening and metallicity. The galaxies span a factor of ∼100 in star formation rate (SFR) and in their surface density of star formation and molecular gas (Σ _SFR , Σ H 2 ), and cover a broad range of morphologies. We find that cluster mass functions are well described by a power law, dN / dM ∝ M ^β , with β = −1.9 ± 0.2, and that this shape is remarkably similar across all galaxies in our sample and eight composite groups of galaxies with similar SFRs, with no significant dependence on SFR, Σ _SFR , or Σ H 2 . Cluster age distributions decline steeply and can be described by dN / dτ ∝ τ ^γ with γ = −0.83 ± 0.24, again with little dependence on host-galaxy properties or cluster mass. The independence of the mass and age distributions implies a separable joint distribution, g ( M , τ ) ∝ M ^β τ ^γ , and suggests that cluster populations in spiral disks are dominated by strong, mass-independent dissolution over their first approximately gigayear. These results establish a benchmark for interpreting cluster demographics across diverse galactic environments and provide context for studies of young cluster populations at high redshift.

We report JWST NIRCAM and MIRI observations of Sgr B2, one of the most active sites of star formation in the Galaxy. These observations, using 14 filters spanning 1.5–25 μ m, have revealed a multilayered and highly structured cloud that contains both a revealed, low-extinction and hidden, high-extinction population of massive stars. JWST has detected new candidate H ii regions around massive stars previously missed by radio telescopes. MIRI has detected radiation escaping from the forming massive cluster Sgr B2 N along its outflow cavities, demonstrating that infrared radiation finds geometric escape routes even in the densest, most heavily embedded regions in the universe. JWST further highlights the gas asymmetry in the cloud, showing a sharp, straight cutoff along the eastern cloud edge. Despite the great sensitivity of these observations, no extended population of young stellar objects has been detected, placing a limit on their minimum extinction; this result hints that star formation has only just begun in the cloud. Together, these results suggest that, despite already holding the crown for one of the most actively star-forming clouds, we have underestimated the total star formation in Sgr B2. JWST unveils previously hidden massive stars and ionized structures, offering the clearest view yet of how stars form under some of the most extreme Galactic conditions.

High-resolution JWST-MIRI images allow us to resolve the multi-scale nature of the emission in nearby star-forming galaxies in great detail, from compact star-forming regions to large-scale diffuse emission, providing new insights into dust emission, its composition, and the surrounding interstellar medium (ISM). We aim to understand at which scale the different processes driving dust emission in mid-infrared (7.7--21 ) wavelengths take place and whether we can disentangle emission from dense regions from the one linked to a more diffuse component. We use and enhance the Constrained Diffusion Decomposition algorithm (CDD), an alternative to wavelet transform decomposition, to disentangle the emission from compact regions from the emission originating from diffuse sources. This allows us to quantify the mid-IR spectral properties of the ISM at intervals within a continuum of physical scales. We find a transition scale for Polycyclic Aromatic Hydrocarbons (PAH) emission around 300 pc, with a weaker PAH fraction at smaller scales, highlighting the destruction of PAHs in regions. We also show variations in the PAH fraction in different morphological environments, with a lower fraction in bright and star-forming environments. By studying and comparing the probability distribution functions (PDFs) of regions and of diffuse ISM with the PDFs at different scales, we find a similar separation scale around 200 pc at which we observe a transition from a power-law PDF for dense structures to a log-normal distribution for the diffuse ISM. We infer the destruction of PAHs in nebular environments and the existence of a transition scale between stellar feedback in nebular regions and heating in the diffuse ISM. We also show that the CDD enables future applications to study the physical scales of emission.