arXiv subjects

A. Della Croce

Publications and source records attributed to A. Della Croce.

11 recordsLinked to original sources

arXiv2026

The evolution of high-z proto-star clusters into local globular clusters

The James Webb Space Telescope (JWST) detected numerous massive and relatively compact stellar clumps around proto-galaxies at high redshift (z>0.5). Their properties suggest that these systems may represent proto-globular clusters (GCs), but their possible connection to local old GCs is poorly understood. In this Letter, we explore the dynamical evolution of proto-star clusters, building the missing evolutionary link between high-z systems observed by JWST and local GCs. Our simulations include the effects of stellar interactions, stellar evolution, and the strong time-dependent cosmological tidal field in which these proto-star clusters evolve. We also explore the role of multiple stellar populations and stellar-mass black holes (BHs), two fundamental ingredients in stellar cluster dynamics. We show that systems hosting multiple populations (as routinely observed in local GCs) are more likely to endure the early strong tidal field than single-population clusters. In addition, after 12 Gyr, such systems have properties consistent with those of Galactic GCs. Our work confirms that the high-z clumps observed by JWST can be the progenitors of the local GCs. Finally, we show that a population of stellar-mass BHs within a proto-star cluster favors its disruption, but that surviving systems can retain a sizable population of BHs.

astro-ph.GA↗

arXiv2026

The Hubble Missing Globular Clusters Survey IV. Ultra-faint compact satellites of the Milky Way. The case of Koposov 2

In the last decades a number of extremely faint and compact Galactic satellites (Ultra Faint Compact Satellites; UFCS) have been discovered by large panoramic surveys. Their nature is uncertain due to their location in the overlapping dwarf galaxy-star cluster region of the $M_V-R_h$ plane and their faintness and distance. Here we show how the deep HST photometry from the Missing Globular Clusters Survey (MGCS), combined with spectroscopic metallicities, provides new insight into the nature of these satellites through accurate distance and age estimates. We consider the case of Koposov 2, currently the most metal-poor bound star cluster known in the Milky Way or an extreme case of Ultra Faint Dwarf galaxy. By performing a spectroscopically-informed bayesian isochrone fit on the MGCS data we find $(m-M)_0=16.85\pm0.06$ ($D=23.4\pm0.6$ kpc) and age=$13.7^{+0.9}_{-1.3}$ Gyr, showing that, contrary to previous age estimates, Koposov 2 is as old as the oldest Galactic globular clusters. The luminosity function, corrected for incompleteness, is well reproduced by a model with the same age and metallicity and a slope of the mass function $x=-0.35$, suggesting a significant depletion of faint stars. We model the surface stellar density field, deriving new robust estimates of the half-light radius ($R_h=0.39^{+0.06}_{-0.04}$ arcsec, corresponding to $R_h=2.7^{+0.4}_{-0.3}$ pc), of the absolute integrated magnitude ($M_V=-0.95\pm0.22$) and of the stellar mass $M_\star=371.8\pm41.6M_{\odot}$), showing that Koposov 2 is much more compact than confirmed dwarf galaxies of similar stellar mass. The new evidence significantly support the hypothesis that Koposov 2 is a star cluster that may have lost a large fraction of its mass. Finally we show that most UFCS lie in the same locus of the $M_\star-R_h$ plane as Galactic open clusters, hinting to a possible additional channel for their formation.

astro-ph.GA↗

arXiv2026

Right round: onset and long-term evolution of rotation in star clusters

We present the results of a detailed kinematic analysis of a significant fraction of the known population of Galactic star clusters aimed at constraining the physical mechanisms driving the onset and evolution of cluster rotation. Our study reveals for the very first time the presence of rotation in clusters at any age, with about $25\%-30\%$ of systems in the sample showing significant evidence of rotation. This result increases by a factor of $\sim5$ the number of clusters identified as rotators so far and it finally enables an observational reading of cluster rotation as a function of time. Young ($<500$ Myr) clusters show a larger range of rotation velocities than older systems. In addition, at young ages we observe a significantly larger fraction ($50\%-60\%$) of rotating systems than at older ones ($\sim 15\%$). These purely empirical results are compatible with rotation being imprinted during the very early stages of cluster formation and early evolution and then being progressively erased by the long-term effects of dynamical evolution. For the sub-sample of clusters for which we were able to perform a full 3D analysis, we calculated the angle between the internal rotation axis and that of the cluster orbital motion. Interestingly, while for clusters with an age smaller than their orbital period we observe similar fractions of prograde and retrograde systems, more evolved clusters appear to be preferentially prograde. We argue that such a behavior is in qualitative agreement with the expectations for the evolution of systems in which primordial rotation was imprinted by the parent molecular cloud and/or by the following hierarchical cluster assembly processes, and in which internal cluster dynamics and interactions with the Galactic field have induced a torque-driven alignment between cluster rotation and orbital motion.

astro-ph.GA↗

arXiv2025

Leo I: the classical dwarf spheroidal galaxy with the highest dark-matter density

Dwarf spheroidal galaxies (dSphs) are known for being strongly dominated by dark matter (DM), which makes them convenient targets for investigating the DM nature and distribution. Recently, renewed interest in the dSph Leo I has resulted from claims suggesting the presence of a central supermassive black hole (BH), with mass estimates that challenge the typical expectations for dSphs, which are generally thought to host intermediate-mass black holes (IMBHs). However, Pascale et al. 2024 presented new upper limits on the BH mass, which are consistent with the range for IMBHs, solving the concerns raised in previous studies. Building on the analysis of Pascale et al. 2024, we examine the DM properties of Leo I inferred from the dynamical models of that paper. Our results indicate that Leo I is the galaxy with the highest DM density among the classical dSphs, with a central DM density (measured at a distance of $150$ pc from the galaxy centre) $ρ_{150}=35.5_{-4.7}^{+3.8}\times10^7\,M_\odot\,$kpc$^{-3}$. The DM density profile has logarithmic slope $γ_{150}=-0.89_{-0.17}^{+0.21}$ at $150$ pc, in line with literature values. At smaller distances the DM distribution flattens into a core, with a core radius of $r_c=72^{+40}_{-32}$ pc. Combined with the small pericentric distance of Leo I's orbit in the Milky Way, the new estimate of $ρ_{150}$ makes Leo I decisive in the study of the anticorrelation between pericentre and central DM density, and suggests that the anticorrelation could be significantly steeper and more pronounced than previously estimated. Despite its DM dominance, Leo I does not emerge as the most favorable target for indirect DM detection: the inferred DM decay $D$ and annihilation $J$ factors, $\log D(0.5^{\circ})$ [GeV cm$^{-2}$] = $17.94_{-0.25}^{+0.17}$ and $\log J(0.5^{\circ})$ [GeV$^2$ cm$^{-5}$]= $18.13_{-0.18}^{+0.17}$ are consistent with previous estimates.

astro-ph.GA↗

arXiv2025

Tracing the W3/W4/W5 and Perseus complex dynamical evolution with star clusters

The Perseus complex offers an ideal testbed to study cluster formation and early evolution as it hosts two major hierarchical structures (namely LISCA I and LISCA II) and the W3/W4/W5 (W345) region characterized by recent star formation. This work aims to provide a full characterization of the population of star clusters in the W345 region, in terms of their structural, photometric, and kinematic properties. Clusters are then used to probe the dynamical properties of the W345 region and, on a larger scale, to investigate the evolution of the Perseus complex. We used Gaia DR3 data to search for star clusters in the W345 region and characterize them in terms of their density structure, ellipticity, internal dynamical state, and ages. We identified five stellar clusters belonging to the W345 complex. The three younger clusters are still partially embedded in the gas and show evidence of expansion, while the older ones cleared the surrounding gas. We also found that YSOs trace the parent gas structure and possibly its kinematics. Thanks to the 6D information available for star clusters, we followed their orbital evolution to assess the formation conditions and evolution of the complex. When accounting for the Galactic potential, we find that the Perseus complex is not dispersing. The observed expansion might be a projection effect due to stars orbiting the Galaxy at different velocities. In addition, we find that the LISCA I and W345 systems formed some $20-30$ Myr ago just a few hundred parsecs away, while LISCA II was originally $\simeq 0.75-1$ kpc apart. Finally, we also assessed the impact of spiral arm perturbations by constructing tailored Galactic potential which matches the observed Galactic spiral arm structure. We find spiral structures drag star clusters toward higher-density regions, possibly keeping clusters closer for longer than the unperturbed, axisymmetric case.

astro-ph.GA↗

arXiv2025

pastamarkers 2: pasta sauce colormaps for your flavorful results

In the big data era of Astrophysics, the improvement of visualization techniques can greatly enhance the ability to identify and interpret key features in complex datasets. This aspect of data analysis will become even more relevant in the near future, with the expected growth of data volumes. With our studies, we aim to drive progress in this field and inspire further research. We present the second release of pastamarkers, a Python-based matplotlib package that we initially presented last year. In this new release we focus on big data visualization and update the content of our first release. We find that analyzing complex problems and mining large data sets becomes significantly more intuitive and engaging when using the familiar and appetizing colors of pasta sauces instead of traditional colormaps.

astro-ph.IM↗

arXiv2024

A 3D view of multiple populations kinematics in Galactic globular clusters

We present the first 3D kinematic analysis of multiple stellar populations (MPs) in a representative sample of 16 Galactic globular clusters (GCs). For each GC in the sample we studied the MP line-of-sight, plane-of-the-sky and 3D rotation as well as the velocity distribution anisotropy. The differences between first- (FP) and second-population (SP) kinematic patterns were constrained by means of parameters specifically defined to provide a global measure of the relevant physical quantities and to enable a meaningful comparison among different clusters. Our analysis provides the first observational description of the MP kinematic properties and of the path they follow during the long-term dynamical evolution. In particular, we find evidence of differences between the rotation of MPs along all velocity components with the SP preferentially rotating faster than the FP. The difference between the rotation strength of MPs is anti-correlated with the cluster dynamical age. We observe also that FPs are characterized by isotropic velocity distributions at any dynamical age probed by our sample. On the contrary, the velocity distribution of SP stars is found to be radially anisotropic in dynamically young clusters and isotropic at later evolutionary stages. The comparison with a set of numerical simulations shows that these observational results are consistent with the long-term evolution of clusters forming with an initially more centrally concentrated and more rapidly rotating SP subsystem. We discuss the possible implications these findings have on our understanding of MP formation and early evolution.

astro-ph.GA↗

arXiv2024

Inference of black-hole mass fraction in Galactic globular clusters. A multi-dimensional approach to break the initial-condition degeneracies

Context. Globular clusters (GCs) are suggested to host many stellar-mass black holes (BHs) at their centers, thus resulting in ideal testbeds for BH formation and retention theories. BHs are expected to play a major role in GC structural and dynamical evolution and their study has attracted a lot of attention. In recent years, several works attempted to constrain the BH mass fraction in GCs typically by comparing a single observable (for example mass segregation proxies) with scaling relations obtained from numerical simulations. Aims. We aim to uncover the possible intrinsic degeneracies in determining the BH mass fraction from single dynamical parameters and identify the possible parameter combinations that are able to break these degeneracies. Methods. We used a set of 101 Monte Carlo simulations sampling a large grid of initial conditions. In particular, we explored the impact of different BH natal kick prescriptions on widely adopted scaling relations. We then compared the results of our simulations with observations obtained using state-of-the-art HST photometric and astrometric catalogs for a sample of 30 Galactic GCs. Results. We find that using a single observable to infer the present-day BH mass fraction in GCs is degenerate, as similar values could be attained by simulations including different BH mass fractions. We argue that the combination of mass-segregation indicators with GC velocity dispersion ratios could help us to break this degeneracy efficiently. We show that such a combination of parameters can be derived with currently available data. However, the limited sample of stars with accurate kinematic measures and its impact on the overall errors do not allow us to discern fully different scenarios yet.

astro-ph.GA↗

arXiv2024

pastamarkers: astrophysical data visualization with pasta-like markers

We aim at facilitating the visualization of astrophysical data for several tasks, such as uncovering patterns, presenting results to the community, and facilitating the understanding of complex physical relationships to the public. We present pastamarkers, a customized Python package fully compatible with matplotlib, that contains unique pasta-shaped markers meant to enhance the visualization of astrophysical data. We prove that using different pasta types as markers can improve the clarity of astrophysical plots by reproducing some of the most famous plots in the literature.

astro-ph.IM↗

arXiv2024

The central black hole in the dwarf spheroidal galaxy Leo I Not supermassive, at most an intermediate-mass candidate

It has been recently claimed that a surprisingly massive black hole (BH) is present in the core of the dwarf spheroidal galaxy (dSph) Leo I. Based on integral field spectroscopy, this finding challenges the typical expectation of dSphs hosting BHs of intermediate-mass, since such a BH would better be classified as supermassive. Indeed, the analysis points toward Leo I harboring a BH with a lower mass limit exceeding a few $10^6M_\odot$ at $1σ$, and the no BH case excluded at 95\% significance. Such a value, comparable to the entire stellar mass of the galaxy, makes Leo I a unique system that warrants further investigations. Using equilibrium models based on distribution functions (DFs) depending on actions $f({\boldsymbol J})$ coupled with the same integral field spectroscopy data and an extensive exploration of a very large parameter space, we demonstrate, within a comprehensive Bayesian framework of model-data comparison, that the posterior on the BH mass is flat towards the low-mass end and, thus, that the kinematics of the central galaxy region only imposes an upper limit on the BH mass of few $10^5M_\odot$ (at $3σ$). Such an upper limit brings back the putative BH of Leo I under the category of intermediate-mass BHs, and it is also in line with formation scenarios and expectations from scaling relations at the mass regime of dwarf galaxies.

astro-ph.GA↗

arXiv2023

Ongoing hierarchical massive cluster assembly: the LISCA II structure in the Perseus complex

We report on the identification of a massive ($\sim10^5$ M$_\odot$) sub-structured stellar system in the Galactic Perseus complex likely undergoing hierarchical cluster assembly. Such a system comprises nine star clusters (including the well-known clusters NGC 654 and NGC 663) and an extended and low-density stellar halo. Gaia-DR3 and available spectroscopic data show that all its components are physically consistent in the 6D phase-space (position, parallax, and 3D motion), homogeneous in age (14 $-$ 44 Myr), and chemical content (half-solar metallicity). In addition, the system's global stellar density distribution is that of typical star clusters and shows clear evidence of mass segregation. We find that the hierarchical structure is mostly contracting towards the center with a speed of up to $\simeq4-5$ km s$^{-1}$, while the innermost regions expand at a lower rate (about $\simeq1$ km s$^{-1}$) and are dominated by random motions. Interestingly, this pattern is dominated by the kinematics of massive stars, while low-mass stars ($M<2$ M$_\odot$) are characterized by contraction across the entire cluster. Finally, the nine star clusters in the system are all characterized by a relatively flat velocity dispersion profile possibly resulting from ongoing interactions and tidal heating. We show that the observational results are generally consistent with those found in $N$-body simulations following the cluster violent relaxation phase strongly suggesting that the system is a massive cluster in the early assembly stages. This is the second structure with these properties identified in our Galaxy and, following the nomenclature of our previous work, we named it LISCA II.

astro-ph.GA↗