Francisco Nogueras-Lara

Context . The Arches cluster, located in the Galactic Centre (GC) is one of the best astrophysical laboratories to study the properties of massive stars and young massive clusters (YMCs). However, despite having been observed for decades at different wavelengths, several fundamental parameters of the Arches cluster remain uncertain. Aims . Our goal is to constrain key cluster parameters – i.e. cluster age, mass, and initial mass function (IMF) – by comparing the observed stellar radio flux density distribution of the Arches cluster to those derived from a set of synthetic clusters. Methods . We used the deep X -band (10 GHz) Very Large Array data from our previous radio continuum study of the Arches cluster. We modelled each simulated cluster with three parameters: age, mass, and IMF slope. We used three different stellar evolutionary models, GENEC, PARSEC, and MIST, at two different metallicities, solar ( Z = 0.014) and super-solar ( Z = 0.020). We ran Markov chain Monte Carlo simulations for each model-metallicity combination to explore parameter space. Results . All models and metallicities return preferred ages in the 2 ≲ t _age /Myr ≲ 3 range. Using radio data alone, we obtained an IMF slope of α _IMF = −1.85 ^+0.28 _−0.20 , averaged over all models, where uncertainties are dominated by the degeneracy between cluster mass and IMF slope. If we use the IMF slope from previous infrared studies as model prior, the cluster mass distributions peak at ∼2.7×10 ⁴ M _⊙ , and we can establish a lower limit at ≳2×10 ⁴ M _⊙ for the Arches cluster mass. Conclusions . Radio continuum observations of their most massive stars can be used to constrain YMC parameters. In the case of the Arches cluster, age can be determined regardless of prior spectroscopic information, which can be useful to characterise newly discovered YMCs in the GC. Furthermore, our results support the idea that a top-heavy IMF may be preferred in the GC or in YMCs in general.

The orbital histories of the dwarf satellites of the Milky Way (MW) are key to understanding their evolution and placing their present-day properties in a dynamical context. We present the results of the orbit integration of 72 dwarfs in the vicinity of the MW, based on accurate 6D phase-space coordinates from the literature and a suite of six realistic, time-evolving gravitational potentials that account for the mutual interaction of the MW and the Large Magellanic Cloud (LMC). We provide the largest catalogue of orbital parameters for MW dwarfs to date, in terms of both galaxy sample size and the range of potentials explored. We also assess the binding status of the dwarfs and estimate their infall times, finding that the majority of them have spent the last 5 Gyr within the MW virial radius. From the reconstructed orbits, we identify ten likely LMC satellites, several of which have experienced very close passages within the LMC stellar disc. For the Small Magellanic Cloud (SMC), we find that its most recent pericentre about the LMC (∼8 kpc, ∼170 Myr ago) is consistent with predictions from the direct collision scenario proposed to explain the LMC’s offset and tilted bar. We also note a broad temporal coincidence between previous SMC pericentres and star formation rate peaks reported in both Magellanic Clouds, suggesting a causal connection. Finally, we identify Grus II and Tucana IV as possible MW satellites recently captured by the LMC, based on their pronounced orbital deflections and velocities relative to the LMC.

The Milky Way hosts a flattened nuclear stellar disc (NSD) that dominates the gravitational potential in the inner few hundred parsecs, but whether the NSD is purely axisymmetric or contains a nuclear bar remains an open question. We tested for the presence of a nuclear bar with kinematic diagnostics, combining positions and line-of-sight velocities from the KMOS NSD survey with proper motions from VIRAC2 to construct the ( v _ℓ , v _los ) velocity ellipse. We measured the vertex deviation ( ℓ _v ) and the anisotropy (β) of the velocity ellipse for a number of sub-samples after applying quality cuts designed to minimise contamination from large-scale bar stars. For our primary sample, comprising stars within | l | < 0.9°, −0.4° < b < 0.25°, and [Fe/H] > −0.3, we measured a negative vertex deviation, l _v = −54.8 _−14.8 ^+13.1° , with moderate anisotropy, β = 0.16 _−0.05 ^+0.08 . A subsample restricted to the innermost four fields yields l _v = −64.3 _−12.2 ^+12.1° with higher anisotropy, β = 0.38 _−0.07 ^+0.12 . The direction of maximum velocity dispersion is oriented along Galactic longitude, contrary to what is observed in samples dominated by large-scale bar stars, where line-of-sight dispersion dominates. We verified the robustness of these signatures against extinction-driven photometric incompleteness, primary-bar contamination, and the choice of metallicity threshold used to suppress bar interlopers; the kinematic measurements remain stable in all cases. The signatures are inconsistent with an NSD that is axisymmetric or oriented orthogonally to the primary bar but match expectations for a nuclear bar oriented at α ≈ 60°-75° to the Sun-Galactic centre line, with its near side pointing towards positive Galactic longitude. While definitive confirmation awaits the larger and more precise samples expected from upcoming surveys, our results provide the first kinematic indication of a possible nuclear bar in the Milky Way.

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.

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.