Maximilian Häberle

Context. Westerlund 1 (Wd1) is the most massive young star cluster known in the Milky Way and a key laboratory for studying the early dynamical evolution of massive clusters. Owing to its high extinction, the internal kinematics of its intermediate-mass stellar population remain largely unexplored. Aims. We aim to characterise the internal kinematic properties of Wd1 using a homogeneous census of near-infrared-selected cluster members and their proper motions (PMs). We considered PMs from the VIRAC2 catalogue, based on multi-epoch VVV/VVVX observations. Methods. For 1286 candidate members previously identified through near-IR photometry and astrometry (Paper I), we computed their PMs relative to the cluster mean motion and analysed them as a function of position and radius. We also investigated radial trends, tested the robustness of the results against the assumed cluster centre, and searched for preferred directions of motion. Results. We detected a statistically significant signature of expansion in the outer regions of Wd1, with the radial component of the relative PMs increasing with distance from the cluster centre. The expansion appears asymmetric, with the strongest gradient detected along a position angle PA= 84° ± 8° in the plane of the sky and with 5.9σ significance. We also found hints of inward radial motions in the central region, consistent with ongoing mass segregation, but only at a ≈2σ significance. Taken together, these results are consistent with a nearly monolithic formation scenario.

The Sloan Digital Sky Survey (SDSS)-V Local Volume Mapper (LVM) is a wide-field integral field spectroscopic survey of the southern Milky Way plane, the Magellanic Clouds, and nearby Local Group galaxies. We used early science observations of the whole body of the nearest nuclear cluster, Omega Centauri, to extend the LVM beyond its primary interstellar-medium science case. The wide LVM field allowed us to precisely map ω Cen’s line-of-sight rotation out to ~3 r _HL or 15′, reaching a maximum value of (8.4 ± 0.8) km s ⁻¹ at r ≈ 4.7′. Within the central region, comparisons with existing VLT MUSE oMEGACat data explicitly show that the unresolved light signal is dominated by a small number of bright stars, with an effective sample size of only ~12 per resolution element. Using Gaia DR3 as an external reference, we verified that the SDSS-V’s LVM reduction pipeline recovers integrated stellar fluxes to 1–4% across six magnitudes of surface brightness. Our resulting total spectrum of ω Cen is one of the highest S/N integrated spectra for any globular or nuclear star cluster. We used it to test four widely used SSP template libraries against the resolved age-metallicity ground truth from oMEGACat. All templates recovered an old, metal-poor population. However, even at signal to noise ratio of ~1300, the inferred mean ages and mean [Fe/H] vary by ~7 Gyr and ~0.4 dex, respectively, across libraries and wavelength ranges, reflecting a systematic floor for integrated-light studies of old multi-population systems.

Omega Centauri ( ω Cen) is the most massive and chemically complex star cluster in the Milky Way (MW) and is widely interpreted as the surviving nuclear star cluster of an accreted dwarf galaxy, although the identity of its parent remains uncertain. We test whether the merger remnants Sequoia, Thamnos, and Gaia–Enceladus (GE) originated in a single progenitor, the ω Dwarf, whose nucleus survives as ω Cen. Combining APOGEE and GALAH abundances with Gaia astrometry, we reconstruct the progenitor’s chemical structure using orbital energy as a proxy for premerger radius. The chemically evolved, younger, Al–N-rich population is strongly concentrated toward the center, consistent with formation during or after the merger. By contrast, the primordial population exhibits dwarf-galaxy-like chemistry across all components, supporting a common origin. Its metallicity profile follows an inverted U-shaped radial trend similar to those observed in present-day nucleated dwarf galaxies. The inner regions, traced by ω Cen and Thamnos, are also more α -enhanced than the outskirts, implying shorter and more efficient star formation and supporting a scenario in which the primordial nucleus assembled partly through the inspiral and merger of globular clusters. Although the chemical evidence permits GE to be associated with ω Dwarf, Sequoia and Thamnos alone form a coherent outside-in stripping sequence around ω Cen. Excluding GE yields a mass–metallicity-relation estimate of 6 . 8 − 3.7 + 8.3 × 1 0 8 M ⊙ for ω Dwarf, whereas including GE increases the inferred mass by a factor of ∼3.4, to 2 . 3 − 1.5 + 4.4 × 1 0 9 M ⊙ . Both estimates are consistent with the nuclear-star-cluster–host-galaxy mass relation, identifying Sequoia and Thamnos as the most robust surviving debris of the ω Cen progenitor.

Optical and NIR magnitude measurements of Low Earth Orbit satellites, from a global observing network - Volume 20 Issue A31

Modern simulations of stellar dynamics in globular clusters peg a dominant role for stellar-mass black holes, but direct evidence for black holes in clusters remains limited. We present the discovery of an astrometric stellar-mass black hole–main sequence star binary in ω Centauri, the most massive Galactic globular cluster, using Hubble Space Telescope data from the oMEGACat project and additional JWST data that span a total of 23 yr. The luminous companion to the black hole is a main-sequence turnoff star, and has a period of 9 4 − 42 + 63 yr, a semimajor axis of 3 1 − 12 + 15 au, and an eccentricity of e = 0.7 2 − 0.13 + 0.08 . Since we observe the binary during periastron, the mass of the black hole is well constrained even though we only observe a partial orbit: the inferred black hole mass is 4.4 6 − 1.01 + 1.22 M _⊙ . We call this black hole oMEGACat BH-2. This is the first astrometric discovery of a stellar-mass black hole in a globular cluster, and is the longest-period black hole binary system yet discovered. The low mass of this black hole is perhaps surprising given the low metallicity of the cluster, and shows that at least some low-mass black holes form at metallicity Z < 10 ⁻³ . We find that the binary is almost certainly dynamically formed and is soft, with an expected binary disruption timescale of ∼800 Myr. While the total number of black hole binaries in ω Centauri is uncertain, we show that existing surveys only cover a small area of parameter space, and that the presence of additional detectable black hole binaries is likely.

Mapping the local and distant Universe is key to our understanding of it. For decades, the Sloan Digital Sky Survey (SDSS) has made a concerted effort to map millions of celestial objects to constrain the physical processes that govern our Universe. The most recent and fifth generation of SDSS (SDSS-V) is organized into three scientific “mappers”: the Milky Way Mapper, which aims to chart the various components of the Milky Way and constrain its formation and assembly; the Black Hole Mapper, which focuses on understanding supermassive black holes in distant galaxies across the Universe; and the Local Volume Mapper, which uses integral field spectroscopy to map the ionized interstellar medium in the Local Group. This paper describes the scope and content for the nineteenth data release (DR19) of SDSS, which is the most substantial to date in SDSS-V. DR19 is the first to contain data from all three mappers. Additionally, we also describe nine value-added catalogs that enhance the science that can be conducted with the SDSS-V data. Finally, we discuss how to access SDSS DR19 and provide illustrative examples and tutorials.

We analyze JWST observations of the central region of the globular cluster ω Centauri (NGC 5139), around the position of the candidate intermediate-mass black hole (IMBH) inferred by M. Häberle et al. from the motion of fast-moving stars in multiepoch Hubble Space Telescope (HST) observations. We performed point-spread-function-fitting photometry for sources in NIRCam (F200W and F444W) and MIRI (F770W and F1500W) and constructed ultraviolet-to-infrared spectral energy distributions (SEDs) for sources within the central region of the cluster, by using HST photometry from oMEGACat. None of the SEDs of the reliably measured sources within this region resemble the SEDs computed from the model of D. W. Pesce et al. for IMBHs accreting from the intracluster medium at low rates. Our JWST limits place constraints on combinations of the IMBH mass and accretion rate, either due to the amount of material available to be accreted or due to the fraction of accreting matter that actually falls into the IMBH. Our nondetection then does not necessarily contradict the mass range of the IMBH inferred from the fast-moving stars. We discuss these constraints in the context of the model of D. W. Pesce et al. We find that the JWST limits are more restrictive than the existing radio limits for IMBH masses ≲6000 M _⊙ . It is also possible that the faint IMBH emission is dominated by the light of a nearby star. Tighter limits on the accretion onto the candidate IMBH can be placed with deeper observations, a more precise localization of the IMBH, and better measurements of the local intracluster medium density and temperature at the center of the cluster.

An understanding of the assembly history of the complex star cluster Omega Centauri has long been sought after, with many studies separating the stars on the color–magnitude diagram into multiple groupings across small magnitude ranges. Utilizing the oMEGACat combined astro-photometric and spectroscopic data set, we parse 14 subpopulations from the upper red giant branch to below the main-sequence turnoff. We combine our results with previous works to estimate the age and age spread of each population. We find that the chemically enhanced (P2) populations are all ∼1 Gyr younger (∼11.6 Gyr old) and have significantly higher intrinsic age spreads (0.6 Gyr) than the primordial (P1) populations (∼12.6 Gyr old, 0.3 Gyr spread), with the intermediate (Im) populations falling in between the two. Additionally, we connect for the first time the chromosome diagram to the two-stream age–metallicity relation, allowing us to link the P1 and P2 stars to the distinct star formation tracks, proposed to be in situ and ex situ contributions to the cluster’s assembly. Our results are consistent with some suggested formation models and rule out others, but no current model can explain all observed features of the subpopulations.

In this paper, we explore the kinematic properties of a sample of 19 young ( < 1 Gyr) and intermediate-age (1–2.5 Gyr) massive star clusters within the Large Magellanic Cloud (LMC). We analysed the proper motions of the clusters, which have been measured based on multi-epoch Hubble Space Telescope (HST) observations. Additionally, from the HST data we inferred homogeneous and robust estimates for the distances, ages, and metallicities of the clusters. This collection of information, in combination with literature line-of-sight velocities, allowed us to investigate the full 3D dynamics of our sample of clusters within the frame of the LMC in a self-consistent way. While most young clusters orbit the LMC close to the stellar disc plane, NGC 1850 (∼100 Myr old) depicts a peculiar case. Depending on the exact distance from the disc, it follows either a highly inclined retrograde orbit or an eccentric orbit along the bar structure. The orbits of young clusters that formed north of the LMC centre show signs that might be connected to the resettling motion of the LMC bar structure. Based on the dynamic properties in combination with the positions of the clusters in the age-metallicity space, we find no clear-cut evidence of clusters in our sample that could have been stripped from the Small Magellanic Cloud (SMC) onto the LMC. Finally, we compared the kinematics of the intermediate-age clusters with a suite of simple numerical simulations of the Magellanic system to interpret the cluster motions. A possible interaction history of the LMC with the SMC, where the SMC had two past crossings of the LMC disc plane (about 300 and 900 Myr ago), in combination with the recent SMC pericentre passage, can qualitatively explain the observed kinematic structure of the clusters analysed in this work.