Populations In Globular Clusters Research Articles

The Dependence of Iron-rich Metal-poor Star Occurrence on Galactic Environment Supports an Origin in Thermonuclear Supernova Nucleosynthesis

It has been suggested that a class of chemically peculiar metal-poor stars called iron-rich metal-poor (IRMP) stars formed from molecular cores with metal contents dominated by thermonuclear supernova nucleosynthesis. If this interpretation is accurate, then IRMP stars should be more common in environments where thermonuclear supernovae were important contributors to chemical evolution. Conversely, IRMP stars should be less common in environments where thermonuclear supernovae were not important contributors to chemical evolution. At constant [Fe/H] ≲ −1, the Milky Way’s satellite classical dwarf spheroidal (dSph) galaxies and the Magellanic Clouds have lower [α/Fe] than the Milky Way field and globular cluster populations. This difference is thought to demonstrate the importance of thermonuclear supernova nucleosynthesis for the chemical evolution of the Milky Way’s satellite classical dSph galaxies and the Magellanic Clouds. We use data from the Sloan Digital Sky Survey Apache Point Observatory Galactic Evolution Experiment and Gaia to infer the occurrence of IRMP stars in the Milky Way’s satellite classical dSph galaxies η dSph and the Magellanic Clouds η Mag, as well as in the Milky Way field η MWF and globular cluster populations η MWGC. In order of decreasing occurrence, we find , , , and a 1σ upper limit η MWGC < 0.00057. These occurrences support the inference that IRMP stars formed in environments dominated by thermonuclear supernova nucleosynthesis and that the time lag between the formation of the first and second stellar generations in globular clusters was longer than the thermonuclear supernova delay time.

Multiple Stellar Populations in Metal-poor Globular Clusters with JWST: A NIRCam View of M92

Recent work on metal-intermediate globular clusters (GCs) with [Fe/H] = −1.5 and −0.75 has illustrated the theoretical behavior of multiple populations in photometric diagrams obtained with the JWST. These results are confirmed by observations of multiple populations among the M dwarfs of 47 Tucanae. Here we explore multiple populations in metal-poor GCs with [Fe/H] = −2.3. We take advantage of synthetic spectra and isochrones that account for the chemical composition of multiple populations to identify photometric diagrams that separate the distinct stellar populations of GCs. We derive high-precision photometry and proper motion for main-sequence (MS) stars in the metal-poor GC M92 from JWST and Hubble Space Telescope images. We identify a first-generation (1G) and two main groups of second-generation (2GA and 2GB) stars and investigate their kinematics and chemical composition. We find isotropic motions with no differences among the distinct populations. The comparison between the observed colors of the M92 stars and the colors derived by synthetic spectra reveals that the helium abundances of 2GA and 2GB stars are higher than those of the 1G by ΔY ∼ 0.01 and 0.04, respectively. The m F090W versus m F090W − m F277W color–magnitude diagram shows that below the knee MS stars exhibit a wide color broadening due to multiple populations. We constrain the amount of oxygen variation needed to reproduce the observed MS width, which is consistent with results on red giant branch stars. We conclude that multiple populations with masses of ∼0.1–0.8 M ⊙ share similar chemical compositions.

The X-Ray Binary-star Cluster Connection in Late-type Galaxies

We conduct one of the largest systematic investigations of bright X-ray binaries (XRBs) in both young star clusters and ancient globular clusters (GCs) using a sample of six nearby star-forming galaxies. Combining complete CXO X-ray source catalogs with optical Physics at High Angular Resolution in Nearby Galaxies-Hubble Space Telescope cluster catalogs, we identify a population of 33 XRBs within or near their parent clusters. We find that GCs that host XRBs in spiral galaxies appear to be brighter, more compact, denser, and more massive than the general GC population. However, these XRB hosts do not appear to be preferentially redder or more metal-rich, pointing to a possible absence of the metallicity-boosted formation of low-mass X-ray binaries (LMXBs) that is observed in the GCs of older galaxies. We also find that a smaller fraction of LMXBs is found in spiral GC systems when compared with those in early-type galaxies: between 8% and 50%, or an average of 20% across galaxies in our sample. Although there is a non-negligible probability of a chance superposition between an XRB and an unrelated young cluster, we find that among clusters younger than 10 Myr, which most likely host high-mass XRBs, the fraction of clusters associated with an XRB increases at higher cluster masses and densities. The X-ray luminosity of XRBs appears to increase with the mass of the cluster host for clusters younger than ∼400 Myr, while the inverse relation is found for XRBs in GCs.

Comparing Globular Cluster System Properties with Host Galaxy Environment* * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with programs 14219 and 15265.

We present Hubble Space Telescope photometry in the optical (F475X) and near-infrared (F110W) bands of the globular cluster (GC) systems of the inner halos of a sample of 15 massive elliptical galaxies. The targets are selected from the volume-limited MASSIVE survey, and chosen to sample a range of environments from sparsely populated groups to the brightest cluster galaxies in dense clusters. We also present a quantitative model of the relation between (F475X − F110W) color and cluster metallicity [M/H], using simulated GCs. Because much of the GC population in such galaxies is built up through accretion, the metallicity distribution of the GC systems might be expected to vary with galaxy environment. The photometry is used to create a completeness-corrected metallicity distribution for each galaxy in the sample, and to fit a double Gaussian curve to each histogram in order to model the two standard red and blue subpopulations. Finally, the properties of the GC metallicity distribution are correlated against galaxy environment. We find that almost no GCS properties and host galaxy environmental properties are correlated, with the exception of a weak but consistent correlation between blue fraction and nth-nearest-neighbor surface density. The results suggest that the systemic properties of the GC systems, at least in the inner to midhalo regions, are influenced more strongly by the local environment at early times, rather than by the environmental properties we see today.

The ages and metallicities of the globular clusters in the Sparkler

ABSTRACT JWST observations of the strongly lensed galaxy the Sparkler have revealed a population of gravitationally bound globular cluster (GC) candidates. Different analyses have resulted in broadly similar ages but significantly different metallicities, questioning the assembly history that has led to the formation of such a population. In this letter, we reanalyse the two sets of photometry available in the literature with the code mcmame especially tailored to fit physical properties of GCs. We find the ages and metallicities from both data sets are consistent within 1σ uncertainties. A significant group of GCs is consistent with being old and metal poor ([Fe/H] ∼ −1.7). For this group, the ages do not converge, hence, we conclude that they are definitively older than 1 Gyr and can be as old as the age of the Universe. The remaining GCs have younger ages and a metallicity spread. The ages and metallicities distribution of GCs in the Sparkler are consistent with those observed in Local Group’s galaxies at similar lookback times. Comparing with predictions from E-MOSAICS simulations we confirm that the Sparkler GC population traces the self-enrichment history of a galaxy which might become a few times 109 M⊙ massive system at redshift z = 0.

GaiaData Release 3

GaiaData Release 3 provides novel flux-calibrated low-resolution spectrophotometry for ≃220 million sources in the wavelength range 330 nm ≤λ≤ 1050 nm (XP spectra). Synthetic photometry directly tied to a flux in physical units can be obtained from these spectra for any passband fully enclosed in this wavelength range. We describe how synthetic photometry can be obtained from XP spectra, illustrating the performance that can be achieved under a range of different conditions – for example passband width and wavelength range – as well as the limits and the problems affecting it. Existing top-quality photometry can be reproduced within a few per cent over a wide range of magnitudes and colour, for wide and medium bands, and with up to millimag accuracy when synthetic photometry is standardised with respect to these external sources. Some examples of potential scientific application are presented, including the detection of multiple populations in globular clusters, the estimation of metallicity extended to the very metal-poor regime, and the classification of white dwarfs. A catalogue providing standardised photometry for ≃2.2 × 108sources in several wide bands of widely used photometric systems is provided (GaiaSynthetic Photometry Catalogue; GSPC) as well as a catalogue of ≃105white dwarfs with DA/non-DA classification obtained with a Random Forest algorithm (GaiaSynthetic Photometry Catalogue for White Dwarfs; GSPC-WD).

The distribution of globular clusters in kinematic spaces does not trace the accretion history of the host galaxy

Context. Reconstructing how all the stellar components of the Galaxy formed and assembled over time by studying the properties of the stars that form it is the aim of Galactic archaeology. Thanks to the launch of the ESA Gaia astrometric mission and the development of many spectroscopic surveys in recent years, we are for the first time in the position to delve into the layers of the past of the Galaxy. Globular clusters play a fundamental role in this research field since they are among the oldest stellar systems in the MW and thus bear witness to its entire past. Aims. As a natural result of galaxy formation, globular clusters did not necessarily all form in the Galaxy itself. Indeed, a fraction of them could have been formed in satellite galaxies accreted by the Milky Way over time. In recent years, there have been several attempts to constrain the nature of clusters (accreted or formed in the Milky Way itself) through the analysis of kinematic spaces, such as the E − Lz, Lperp − Lz, eccentricity − Lz, and the action space, as well as attempts to reconstruct the properties of the accretion events experienced by the Milky Way through time from this kind of analysis. This work aims to test a widely used assumption about the clustering of the accreted populations of globular clusters in the integrals of motions space. Methods. In this paper we analyse a set of dissipationless N-body simulations that reproduce the accretion of one or two satellites with their globular cluster population on a Milky Way-type galaxy. Results. Our results demonstrate that a significant overlap between accreted and ‘kinematically heated’ in situ globular clusters is expected in kinematic spaces for mergers with mass ratios of 1:10. In contrast with the standard assumptions made in the literature so far, we find that accreted globular clusters do not show dynamical coherence, that is, they do not cluster in kinematic spaces. In addition, we show that globular clusters can also be found in regions dominated by stars that have a different origin (i.e. a different progenitor). This casts doubt on the association between clusters and field stars that is generally made in the literature and is used to assign them to a common origin. By means of Gaussian mixture models, we demonstrate that the overlap of clusters is not only a projection effect on specific planes but is also found when the whole set of kinematic properties (i.e. E, Lz, Lperp, eccentricity, radial, and vertical actions) is taken into account. Overall, our findings severely question the recovered accretion history of the Milky Way based on the phase-space clustering of the globular cluster population.

The e-TidalGCs project

We present the e-TidalGCs project, aimed at modeling and predicting the extra-tidal features surrounding all Galactic globular clusters for which 6D phase-space information, masses, and sizes are available (currently numbering 159 globular clusters). We focus the analysis and presentation of the results on the distribution of extra-tidal material on the sky, as well as on the different structures found at different heliocentric distances. We emphasize the wide variety of morphologies found: beyond the canonical tidal tails, our models reveal that the extra-tidal features generated by globular clusters take a wide variety of shapes, from thin and elongated shapes to thick and complex halo-like structures. We also compare some of the most well-studied stellar streams found around Galactic globular clusters to our model predictions, namely, those associated with the clusters NGC 3201, NGC 4590, NGC 5466, and Pal 5. Additionally, we investigate how the distribution and extension in the sky of the simulated streams vary with the Galactic potential by making use of three different models, either containing a central spheroid, not containing one, or containing a stellar bar. Overall, our models predict that the mass lost by the current globular cluster population in the field from the last 5 Gyrs is between 0.3 − 2.1 × 107 M⊙. This amount is comparable to a value between 7–55% of the current mass. Most of this lost mass is found in the inner Galaxy, with the half-mass radius of this population being between 4–6 kpc. The outputs of the simulations will be publicly available, coinciding with the unique opportunity presented by the delivery of the ESA Gaia mission and complementary spectroscopic surveys. Their exquisite data will offer the possibility to carry out novel comparisons with the models discussed in this work.

Formation of star clusters and enrichment by massive stars in simulations of low-metallicity galaxies with a fully sampled initial stellar mass function

ABSTRACT We present new griffin project hydrodynamical simulations that model the formation of galactic star cluster populations in low-metallicity (Z = 0.00021) dwarf galaxies, including radiation, supernova, and stellar wind feedback of individual massive stars. In the simulations, stars are sampled from the stellar initial mass function (IMF) down to the hydrogen-burning limit of 0.08 M⊙. Mass conservation is enforced within a radius of 1 pc for the formation of massive stars. We find that massive stars are preferentially found in star clusters and follow a correlation set at birth between the highest initial stellar mass and the star cluster mass that differs from pure stochastic IMF sampling. With a fully sampled IMF, star clusters lose mass in the galactic tidal field according to mass-loss rates observed in nearby galaxies. Of the released stellar feedback, 60 per cent of the supernova material and up to 35 per cent of the wind material reside either in the hot interstellar medium (ISM) or in gaseous, metal-enriched outflows. While stellar winds (instantaneously) and supernovae (delayed) start enriching the ISM right after the first massive stars form, the formation of supernova-enriched stars and star clusters is significantly delayed (by &amp;gt;50 Myr) compared to the formation of stars and star clusters enriched by stellar winds. Overall, supernova ejecta dominate the enrichment by mass, while the number of enriched stars is determined by continuous stellar winds. These results present a concept for the formation of chemically distinct populations of stars in bound star clusters, reminiscent of multiple populations in globular clusters.

Multiple stellar populations in globular clusters with JWST: an NIRCam view of 47 Tucanae

ABSTRACT We use images collected with the near-infrared camera (NIRCam) onboard the JWST and with the Hubble Space Telescope (HST) to investigate multiple populations at the bottom of the main sequence (MS) of 47 Tucanae. The mF115W versus mF115W − mF322W2 colour–magnitude diagram (CMD) from NIRCam shows that, below the knee, the MS stars span a wide colour range, where the majority of M-dwarfs exhibit blue colours, and a tail of stars are distributed towards the red. A similar pattern is observed from the mF160W versus mF110W − mF160W CMD from HST, and multiple populations of M-dwarfs are also visible in the optical mF606W versus mF606W − mF814W CMD. The NIRCam CMD shows a narrow sequence of faint MS stars with masses smaller than $0.1\, \mathcal {M}_{\odot }$. We introduce a chromosome map of M-dwarfs that reveals an extended first population and three main groups of second-population stars. By combining isochrones and synthetic spectra with appropriate chemical composition, we simulate colours and magnitudes of different stellar populations in the NIRCam filters (at metallicities [Fe/H] = −1.5 and [Fe/H] = −0.75) and identify the photometric bands that provide the most efficient diagrams to investigate the multiple populations in globular clusters. Models are compared with the observed CMDs of 47 Tucanae to constrain M-dwarfs’ chemical composition. Our analysis suggests that the oxygen range needed to reproduce the colours of first- and second-population M-dwarfs is similar to that inferred from spectroscopy of red giants, constraining the proposal that the chemical variations are due to mass transfer phenomena in proto-clusters.

The large-scale structure of globular clusters in the NGC 1052 group

ABSTRACT Prompted by the many controversial claims involving the NGC 1052 group, including that it hosts two dark matter-free galaxies with overluminous and monochromatic globular cluster (GC) systems, here, we map out the large-scale structure (LSS) of GCs over the entire group. To recover the LSS, we use archival optical CFHT imaging data. We recover two GC density maps, one based on universal photometric properties of GCs from simple stellar population models, and one based on the properties of spectroscopically confirmed GCs in DF2 and DF4 (the two dwarf galaxies with overluminous GC populations). Both selection methods reveal overdensities around the massive galaxies in the group, as well as around NGC 1052 itself, that are coincident with the positions of previously identified stellar streams and tidal features. No intragroup GCs are found connecting these structures to any of the dwarf galaxies. We find, however, two other dwarfs in the group hosting GC systems. These include RCP32 with two GCs with ages equivalent to the GCs around NGC 1052 and DF9 with three GCs with ages similar to the GCs around DF2 and DF4. We conclude that the GC distribution in the group does not strongly support any formation scenario in particular. It favours, none the less, scenarios relying on galaxy–galaxy interactions and on the coeval formation of GCs around the DM-free dwarf galaxies. These may include the recently proposed bullet-dwarf formation, as well as high-redshift tidal dwarf galaxy models.

Globular Cluster UVIT Legacy Survey (GlobULeS) – II. Evolutionary status of hot stars in M3 and M13

ABSTRACT We present a far-ultraviolet (FUV) study of hot stellar populations in the second parameter pair globular clusters (GCs) M3 and M13, as a part of the GC UVIT Legacy Survey programme (GlobULeS). We use observations made with F148W and F169M filters of the Ultraviolet Imaging Telescope (UVIT) onboard AstroSat along with ground-based data (UBVRI filters), Hubble Space Telescope(HST) GC catalogue, and Gaia EDR3 catalogue. Based on the FUV-optical colour–magnitude diagrams, we classify the sources into the horizontal branch (HB) stars, post-HB stars, and hot white dwarfs (WDs) in both the GCs. The comparison of synthetic and observed colours of the observed HB stars suggests that the mass-loss at the red giant branch and He spread in both clusters have a simultaneous effect on the different HB distributions detected in M3 and M13, such that HB stars of M13 require a larger spread in He (0.247–0.310) than those of M3 (Y = 0.252–0.266). The evolutionary status of HB stars, post-HB stars, and WDs are studied using SED fit parameters and theoretical evolutionary tracks on the H–R diagram. We found that the observed post-HB stars have evolved from zero-age HB (ZAHB) stars of the mass range of 0.48−0.55 M⊙ in M3 and M13. We detect 24 WD candidates in each cluster having ${\rm \log ({\it L}_{bol}/L_\odot)}$ in the range of −0.8 to +0.6 and ${\rm \log ({\it T}_{eff}/K)}$ in the range of 4.2–5.0. Placing the WDs on the H–R diagram and comparing them with models, it is found that M13 has a population of low-mass WDs, probably originating from binary evolution.

A trail of the invisible: blue globular clusters trace the radial density distribution of the dark matter – case study of NGC 4278

ABSTRACTWe present new, deep optical observations of the early-type galaxy NGC 4278, which is located in a small loose group. We find that the galaxy lacks fine substructure, that is, it appears relaxed, out to a radius of ∼70 kpc. Our g- and i-band surface brightness profiles are uniform down to our deepest levels of ∼28 mag arcsec−2. This spans an extremely large radial range of more than 14 half-mass radii. Combined with archival globular cluster (GC) number density maps and a new analysis of the total mass distribution obtained from archival Chandra X-ray data, we find that the red GC subpopulation traces well the stellar mass density profile from 2.4 out to even 14 half-mass radii, while the blue GC subpopulation traces the total mass density profile of the galaxy over a large radial range. Our results reinforce the scenario that red GCs form mostly in situ along with the stellar component of the galaxy, while the blue GCs are more closely aligned with the total mass distribution in the halo and were accreted along with halo matter. We conclude that for galaxies where the X-ray emission from the hot halo is too faint to be properly observable and as such is not available to measure the dark matter profile, the blue GC population can be used to trace this dark matter component out to large radii.

Kinematic differences between multiple populations in Galactic globular clusters

Aims. The formation process of multiple populations in globular clusters is still up for debate. These populations are characterized by different light-element abundances. Kinematic differences between the populations are particularly interesting in this respect because they allow us to distinguish between single-epoch formation scenarios and multi-epoch formation scenarios. We derive rotation and dispersion profiles for 25 globular clusters and aimed to find kinematic differences between multiple populations to constrain their formation process. Methods. We split red-giant-branch (RGB) stars in each cluster into three populations (P1, P2, and P3) for the type-II clusters and two populations (P1 and P2) otherwise using Hubble photometry. We derived the global rotation and dispersion profiles for each cluster by using all stars with radial velocity measurements obtained from MUSE spectroscopy. We also derived these profiles for the individual populations of each cluster. Based on the rotation and dispersion profiles, we calculated the rotation strength in terms of ordered-over-random motion, (v/σ)HL, evaluated at the half-light radius of the cluster. We then consistently analyzed all clusters for differences in the rotation strength of their populations. Results. We detect rotation in all but four clusters. For NGC 104, NGC 1851, NGC 2808, NGC 5286, NGC 5904, NGC 6093, NGC 6388, NGC 6541, NGC 7078, and NGC 7089, we also detect rotation for P1 and/or P2 stars. For NGC 2808, NGC 6093, and NGC 7078 we find differences in (v/σ)HL between P1 and P2 that are larger than 1σ. Whereas we find that P2 rotates faster than P1 for NGC 6093 and NGC 7078, the opposite is true for NGC 2808. However, even for these three clusters the differences are still of low significance. We find that the rotation strength of a cluster generally scales with its median relaxation time. For P1 and P2 the corresponding relation is very weak at best. We observe no correlation between the difference in rotation strength between P1 and P2 and the cluster relaxation time. The stellar radial velocities derived from MUSE data that this analysis is based on are made publicly available.

Evidence for a bottom-light initial mass function in massive star clusters

ABSTRACT We have determined stellar mass functions of 120 Milky Way globular clusters and massive Large Magellanic Cloud/Small Magellanic Cloud star clusters based on a comparison of archival Hubble Space Telescope photometry with a large grid of direct N-body simulations. We find a strong correlation of the global mass function slopes of star clusters with both their internal relaxation times and their lifetimes. Once dynamical effects are being accounted for, the mass functions of most star clusters are compatible with an initial mass function described by a broken power-law distribution N(m) ∼ mα with break masses at 0.4 and 1.0 M⊙ and mass function slopes of αLow = −0.3 for stars with masses m &amp;lt; 0.4 M⊙, αHigh = −2.30 for stars with m &amp;gt; 1.0 M⊙, and αMed = −1.65 for intermediate-mass stars. Alternatively, a lognormal mass function with a characteristic mass log MC = −0.36 and width σC = 0.28 for low-mass stars and a power-law mass function for stars with m &amp;gt; 1 M⊙ also fit our data. We do not find a significant environmental dependence of the initial mass function on cluster mass, density, global velocity dispersion, or metallicity. Our results lead to a larger fraction of high-mass stars in globular clusters compared to canonical Kroupa/Chabrier mass functions, increasing the efficiency of self-enrichment in clusters and helping to alleviate the mass budget problem of multiple stellar populations in globular clusters. By comparing our results with direct N-body simulations, we finally find that only simulations in which most black holes are ejected by natal birth kicks correctly reproduce the observed correlations.

Self-Enrichment in Globular Clusters: The Crucial Role Played by Oxygen

Results from photometry and high-resolution spectroscopy have demonstrated the existence of multiple populations in globular clusters, where one or more stellar generations of stars coexist with the original population. We study the possibility that the new generation(s) of stars formed from the gas lost by intermediate mass (4–8 M⊙) stars during the asymptotic giant branch (AGB) evolution, possibly after dilution with residual pristine gas in the cluster. To this aim, we confront the chemistry of the AGB ejecta with the distribution of the chemical composition of stars in NGC 6402. We find that a satisfactory consistency between the observational evidence and the self-enrichment by AGBs hypothesis is reached if the mass-loss rates experienced for the latter stars is ∼10 times smaller than found for the solar metallicity counterparts of the same mass. We also comment on the importance of the knowledge of the oxygen abundance as a key indicator of the extent of the nucleosynthesis at which the gas from which the stars belonging to the second generation of the clusters formed, and the degree of dilution with pristine gas.

The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XXIV. Differences in Internal Kinematics of Multiple Stellar Populations

Our understanding of the kinematic properties of multiple stellar populations (mPOPs) in Galactic globular clusters (GCs) is still limited compared to what we know about their chemical and photometric characteristics. Such limitation arises from the lack of a comprehensive observational investigation of this topic. Here we present the first homogeneous kinematic analysis of mPOPs in 56 GCs based on high-precision proper motions computed with Hubble Space Telescope data. We focused on red-giant-branch stars, for which the mPOP tagging is clearer, and measured the velocity dispersion of stars belonging to first (1G) and second generations (2G). We find that 1G stars are generally kinematically isotropic even at the half-light radius, whereas 2G stars are isotropic at the center and become radially anisotropic before the half-light radius. The radial anisotropy is induced by a lower tangential velocity dispersion of 2G stars with respect to the 1G population, while the radial component of the motion is comparable. We also show possible evidence that the kinematic properties of mPOPs are affected by the Galactic tidal field, corroborating previous observational and theoretical results suggesting a relation between the strength of the external tidal field and some properties of mPOPs. Although limited to the GCs’ central regions, our analysis leads to new insights into the mPOP phenomenon, and provides the motivation for future observational studies of the internal kinematics of mPOPs.

Multiple Populations in Low-mass Globular Clusters: Eridanus

Multiple populations (MPs), characterized by variations in light elemental abundances, have been found in stellar clusters in the Milky Way, Magellanic Clouds, as well as several other dwarf galaxies. Based on a large number of observations, mass has been suggested to be a key parameter affecting the presence and appearance of MPs in stellar clusters. To further investigate the existence of MPs in low-mass clusters and explore the mass threshold for the formation of MPs, we carried out a project studying the composition of the stellar population in several low-mass Galactic globular clusters. Here we present our study on the cluster Eridanus. With blue-UV low-resolution spectra obtained with the OSIRIS/Multi-object spectrograph on the Gran Telescopio Canarias, we computed the spectral indices of CH and CN for a sample of giant stars and derived their carbon and nitrogen abundances using model spectra. A significant dispersion in the initial surface abundance of nitrogen was found in the sample, indicating the existence of MPs in Eridanus. Inspecting the age–initial mass distribution of in situ clusters with MPs, we find a slight trend that initial mass increases with increasing age, and the lowest initial masses of ∼ 4.98 and 5.26 are found at the young and old end, respectively, which might provide a rough reference for the mass threshold for clusters to form MPs. However, more observations of clusters with low initial masses are still necessary before any firm conclusion can be drawn.

MOCCA-Survey Database: extra galactic globular clusters – III. The population of black holes in Milky Way and Andromeda-like galaxies

ABSTRACT This work investigates the black hole (BH) population of globular clusters (GCs) in Milky Way- and Andromeda-like galaxies. We combine the population synthesis code MASinGa and the MOCCA-Survey Database I to infer the properties of GCs harbouring a stellar-mass BH subsystem (BHS), an intermediate-mass BH (IMBH), or neither of those. We find that the typical number of GCs with a BHS, an IMBH, or none become comparable in the galactic outskirts, whilst the inner galactic regions are dominated by GCs without a significant dark component. We retrieve the properties of binary BHs (BBHs) that have either merged in the last 3 Gyr or survived in their parent cluster until present-day. We find that around 80 per cent of the merging BBHs form due to dynamical interactions while the remaining originate from evolution of primordial binaries. The inferred merger rate for both in-cluster and ejected mergers is $1.0\!-\!23\, \, \rm {yr^{-1}\, Gpc^{-3}}$ in the local Universe, depending on the adopted assumptions. We find around 100–240 BBHs survive in GCs until present-day and are mostly concentrated in the inner few kpc of the galaxy. When compared with the field, GCs are at least two times more efficient in the formation of BHs and binaries containing at least one BH. Around 1000–3000 single BHs and 100–200 BBHs are transported into the galactic nucleus from infalling clusters over a time span of 12 Gyr. We estimate that the number of BHs and BBHs lurking in the star cluster to be about 1.4–2.2 × 104 and 700–1100, respectively.

What the JWST can tell us about the Origin of Multiple Stellar Populations in Globular Clusters

AbstractI present the first results of multiple stellar populations in globular clusters from James Webb Space Telescope (JWST) data. We obtained combined NIRSpec and NIRCam data of the GC 47 Tucanae to investigate the properties of the different stellar populations in the low-mass regime, down to ∼0.5 M⊙. Our analysis of both the photometric data and the spectra suggests that the multiple stellar populations among M dwarfs share similar properties of those extensively studied on bright red giant branch stars. The comparison between stellar populations’ properties at different stellar mass, e.g. at the red giants and M dwarfs’ phases, can potentially provide strong constraints to the formation scenarios of the still eluding phenomenon of the multiple populations in star clusters.