Elisabeth A. C. Mills

We present a multiwavelength analysis of a young bubble in the nuclear starburst of NGC 253 using new JWST MIRI–MRS observations together with archival ALMA (100, 350, 690 GHz) and Chandra data. The MIRI maps reveal a prominent bubble-like structure in both ionized and molecular emission lines. The bubble is spatially coincident with one of the least embedded massive young clusters detected with ALMA, suggesting that the cluster is driving the expansion. We measure a radius of ∼11.5 ± 3.4 pc and an expansion velocity of ∼90 ± 44 km s ⁻¹ , implying a dynamical age of ∼0.1 ± 0.1 Myr. Using RADEX modeling of multiple CO transitions, we infer a molecular mass in the range of (1.3 ± 0.3) × 10 ⁴ to (2.8 ± 0.8) × 10 ⁵ M _⊙ . We derive a kinetic energy on the order 10 ⁵¹⁻⁵² erg, consistent with mechanical input from Wolf–Rayet stellar winds or supernovae in a ∼10 ⁶ M _⊙ cluster. The existence of a large population of Wolf–Rayet stars or past supernovae is supported by the presence of coincident X-ray emission. Our results provide direct evidence that individual clusters in a nuclear environment can carve out coherent structures on parsec scales and inject significant energy and momentum into the surrounding interstellar medium, which can contribute to the nuclear outflow in NGC 253.

We present an analysis of dust kinematics in the local starburst galaxies M82 (NGC 3034) and NGC 253 using polycyclic aromatic hydrocarbon (PAH) features observed with JWST/MIRI spectroscopy. We are able to produce high-quality velocity maps of the 5.2, 6.2, and 11.3 μ m PAH features, as well as numerous lines of molecular gas via H ₂ rotational transitions and ionized gas from [Ne ii ] and H recombination lines. Given the field of view and inclination, we trace a rotating disk in M82 where we observe a steep rise in the velocities followed by flattening, typical of galaxy rotation curves. In NGC 253, however, the 6.2 and 11.3 μ m PAH features trace the launching region of the outflow, firmly within the starburst region. We find the ionized gas also shows outflow contributions in NGC 253 while the warm molecular gas is dominated by rotation. Additionally, the molecular gas outflow velocities are lower than the ionized gas, with the 11.3 μ m PAH feature consistent with the ionized gas rather than the molecular gas. We therefore suggest that PAHs are more closely associated with the ionized gas rather than the molecular at the base of the galaxy outflow, whereas larger-scale imaging shows comparable morphology between PAHs and H I . The 6.2 μ m PAH feature has an even higher outflow velocity for both galaxies, possibly suggesting preferential ionization of the PAHs within the faster-moving hot phase of the base of the outflow.

Elemental and isotopic abundances are key tracers of planet formation, stellar evolution, and Galactic chemical evolution. Very low-mass stars are particularly interesting in this regard, because unlike more massive or evolved stars their photospheric abundances retain the star’s natal composition. Cool dwarf spectra have historically been challenging to use for measurements of chemical abundances because of the blending of molecular and atomic features. However, recent advances in molecular line lists, atmospheric models, fitting techniques, and IR spectrographs have enabled the successful measurement of elemental and isotopic ratios in a few dozen very-low-mass stars. Here, we present near-IR high-resolution spectroscopy of TRAPPIST-1 covering the fundamental and overtone bands of carbon monoxide and its prominent isotopologues. From the joint analysis of the K -band (CFHT/SPIRou) and M -band (Keck/NIRSPEC) spectra, we derive the first stellar C/O ratio and the first carbon- and oxygen-isotope ratios for this star. We obtain a metallicity of [ M / H ] = 0.0 0 − 0.06 + 0.06 , a C/O ratio of 0.6 0 − 0.02 + 0.02 , 12 C / 13 C = 15 4 − 16 + 17 , and 16 O / 18 O = 49 0 − 64 + 78 . TRAPPIST-1 has generally solar-like elemental abundances, with a ¹² C/ ¹³ C that is higher than the solar value and may be modestly elevated relative to some nearby cool dwarfs at similar metallicity. While C/O is most tightly constrained by the K band, the isotopic detections are driven by the M -band data.

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 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.