NGC 1399, the bright central galaxy of the Fornax cluster, contains an extensive population of globular clusters (GCs) extending beyond 200 kpc into its outer halo, approximately 6.5 effective radii (Re). We conducted dynamical mass modelling of NGC 1399 out to 5 Re (∼150 kpc) using the most comprehensive radial velocity catalogue of GCs to date, which includes data from the Fornax cluster VLT Spectroscopic Survey (FVSS) and previous velocity measurements from the literature. Applying spherical Jeans equations, we performed dispersion-kurtosis modelling of NGC 1399’s GC kinematics to derive its mass profile and the orbital anisotropy of its GCs. We also investigated the impact of including intra-cluster GCs in the mass modelling, which were selected based on spatial segregation and a velocity σ-clipping method. Our findings indicate that both cusp-like (NFW) and core-like (Burkert) halos can reproduce the observed kinematics of GCs. Including the intra-cluster GCs in the mass modelling yields broadly consistent mass profiles for the two halo types, with the full GC sample giving a virial mass of log Mvir = 13.81 ± 0.09 M⊙ for the NFW halo, slightly higher than the value inferred for the Burkert halo. Regardless of the dark matter halo profile adopted, we observe that the intra-cluster GCs exhibit radial anisotropy in the outskirts, especially the blue, metal-poor GCs. These results suggest that GCs in NGC 1399’s outer halo are influenced by an additional halo component associated with the galaxy cluster potential. The radial anisotropy observed in these outer-halo GCs provides strong dynamical evidence that they were accreted from external sources, which is consistent with prior photometric and spectroscopic studies of GCs. This study highlights the importance of including intra-cluster GCs in dynamical mass modelling to fully account for the contribution of dark matter to the cluster gravitational potential.
Context. Mercury is an airless body where space weathering processes play a key role in modifying the surface and sustaining the exosphere. Some of these processes are thought to be linked to ion precipitation driven by solar wind–magnetosphere interactions, although the detailed mechanisms remain to be fully understood. Previous studies of solar wind proton precipitation have mainly focused on external factors, such as solar wind and interplanetary magnetic-field conditions, while the role of internal factors has received comparatively little attention. Aims. We aim to investigate how Mercury’s interior conductivity profile, an internal factor, affects solar wind proton precipitation onto the planet’s surface. Methods. We employed Amitis, a hybrid simulation model, to conduct a series of simulations with different interior conductivity profiles and examine their precipitation patterns. We then separated the magnetic fields generated by interior currents from those of other sources to isolate their respective contributions to precipitation. Results. We find that core induction currents shield the equatorial region from precipitation, while interior conduction currents linked to Region-1 field-aligned currents (R1 FACs) reduce dayside shielding and enhance nightside shielding, thereby modulating the day–night asymmetry of the precipitation pattern. In addition, the R1 FAC-related electric field enhances the dawn–dusk asymmetry of precipitation. Conclusions. These findings indicate that the interior conductivity profile substantially influences the solar wind proton precipitation pattern through its associated magnetic and electric fields, with effects that extend beyond the surface into Mercury’s broader coupled environment. The planetary interior should be recognized as an integral component of Mercury’s coupled space environment – alongside the solar wind, magnetosphere, surface, and exosphere – and should not be neglected in future modeling and observational studies.
Context. Satellite mega-constellations have been shown to generate unintended electro-magnetic radiation (UEMR) that impacts low-frequency radio astronomy. The Radio Regulations of the International Telecommunications Union Radiocommunication Sector (ITU-R) contain the logical basis for addressing UEMR, but the enforcement mechanisms are absent. Aims. We aim to adapt compatibility study methods based on satellite constellation simulations, in particular the equivalent power flux-density (EPFD) framework, to real-world radio telescope measurement data. Methods. We adapt the ITU-R EPFD calculation framework to radio astronomy measurement data obtained from all-sky interferometric imaging. We explicitly address the conceptual differences between forward-model EPFD calculations and measurement-based approaches, including antenna gain treatment, temporal averaging, and detection limitations. In particular, we consider low-frequency systems, which are typically wide field-of-view and interferometric instruments. Results. For the first time, we demonstrate that because all-sky interferometric observations can be interpreted as a set of simultaneous beamformed measurements they enable a direct adaptation of the EPFD formalism to measurement data. Applying this framework to low-frequency observations, we confirm previous estimations that the resulting measurement-based EPFD distributions exceed the radio astronomy interference threshold levels defined in Recommendation ITU-R RA.769-2 in approximately 50–70% of samples, depending on polarisation and the observing subset. These exceedance fractions are well above the 2% single-system data-loss criterion in Recommendation ITU-R RA.1513-2. Expressed using the conventional 2% compatibility margin, the corresponding margins are negative, ranging from -18.6 to -16.3 dB, equivalent to a required uniform attenuation of 16.3–18.6 dB. Conclusions. We show that measurement-based implementations provide a practical pathway towards verification and long-term monitoring at low radio frequencies, which could form an important component of enforceability. We suggest instrumentation approaches to support measurement.
Low-mass galaxies beyond the Local Group can only be studied through their integrated light, yet it remains unclear whether structural parameters inferred from integrated light are directly comparable to those obtained from resolved-star studies. Using new deep imaging obtained with small-aperture amateur telescopes, we analyse the classical dwarf spheroidals Leo II, Sculptor, and Fornax, whose stellar distributions have been extensively characterised through resolved-star studies. We find that the radial light distributions and effective radii inferred from integrated light are in excellent agreement with those derived from resolved stars, showing that resolved-star and integrated-light analyses can be placed within a common observational framework applicable across a broad range of distances. The two approaches are highly complementary: resolved-star analyses trace galaxies to very large radii but are limited by stellar crowding in their central regions, whereas integrated-light observations are insensitive to crowding and allow the inner stellar distribution to be traced to substantially smaller radii. The integrated-light analysis extends the structural analysis to radii up to an order of magnitude smaller than previous star-counting studies while significantly reducing the scatter in the measured profiles.
Context. Investigating substellar populations in young massive clusters offers crucial insights into the formation of brown dwarfs (BDs) and the role of environmental conditions in shaping their properties. Westerlund 2 (Wd2), as one of the nearest dense and massive clusters in the Milky Way, represents an ideal laboratory for studying the effects of high stellar density and ionizing radiation from massive stars on BD formation. Aims. This paper presents deep JWST/NIRCam observations of Wd2 in a large number of filters between 1.15 and 4.1 µm. Our analysis focuses on identifying and characterizing the BD population within the cluster. Methods. We carried out point spread function (PSF) photometry on deep JWST/NIRCam data obtained in four wide and six medium-band filters, using DOLPHOT. The resulting catalog was used to identify BD candidates in Wd2 through spectral energy distribution (SED) fitting with atmospheric models. The methodology was validated using synthetic JWST photometry of spectroscopically confirmed young BDs together with simulated populations of typical contaminants, allowing us to define an empirical selection criteria. Results. The 50% detection limit of our NIRCam catalog is ∼0.015–0.02 M⊙, at the distance, age, and extinction of Wd2, providing the deepest view of a supermassive star cluster to date. The validation demonstrates that the adopted SED-fitting methodology reliably recovers young brown dwarfs while remaining robust against contamination from reddened evolved stars. Applying this procedure to Wd2, we identify 353 substellar candidates. Most candidates (301) lie above the 10 Myr isochrone in the Hertzsprung-Russell diagram consistent with cluster membership and are defined as strong candidates. Comparison with a control field indicates a contamination level of ≲5% for the strong candidate sample down to masses of ∼0.01–0.015 M⊙. We identify 73 candidates exhibiting an infrared excess indicative of circumstellar disks. These objects occupy the expected infrared-excess locus in de-reddened color diagrams and represent 27.7+3.4−3.2% of the candidates detected in F410M. Conclusions. These results demonstrate the capability of JWST/NIRCam medium-band photometry to identify robust samples of candidate brown dwarfs in distant, embedded, and crowded massive star clusters using imaging observations alone. The resulting catalog provides a well-characterized sample for future spectroscopic confirmation and subsequent studies of the substellar population of Wd2.
