Globular Clusters (GCs) are generally treated as natural validators of simple stellar population (SSP) models. However, there are still some differences between real GCs and SSPs. In this work we use a direct $N$-body simulation code {\hf Nbody6} to study the influences of dynamical interactions, metallicity and primordial binaries on Milky Way globular clusters' integrated properties. Our models start with $N=100,000$ stars, covering a metallicity range $Z=0.0001-0.02$, a subset of our models contain primordial binaries, resulting in a binary fraction as currently observed at a model age of GCs.Stellar evolution and external tidal field representative for an average Milky Way GC are taken into consideration. The integrated colours and Lick indices are calculated using BaSeL and Bluered stellar spectral libraries separately.
By including dynamical interactions, our model clusters show integrated features (colours up to 0.01mag bluer, H$β$ up to 0.1Å$ $ greater and [MgFe]$'$ 0.05Å$ $ smaller) making the clusters appear slightly younger than the model clusters without dynamical interactions. This effect is caused mainly by the preferential loss of low-mass stars which have a stronger contribution to redder passbands as well as different spectral features compared to higher-mass stars. In addition, this effect is larger at lower metallicities. On the contrary, the incorporation of primordial binaries reduces this effect.
Integrated light (IL) spectroscopy enables studies of stellar populations beyond the Milky Way and its nearest satellites. In this paper, I will review how IL spectroscopy reveals essential information about globular clusters and the assembly histories of their host galaxies, concentrating particularly on the metallicities and detailed chemical abundances of the GCs in M31. I will also briefly mention the effects of multiple populations on IL spectra, and how observations of distant globular clusters help constrain the source(s) of light-element abundance variations. I will end with future per…
We perform integrated spectroscopy of 24 Galactic globular clusters. Spectra are observed from one core radius for each cluster with a high wavelength resolution of ~2.0 A FWHM. In combination with two existing data sets from Puzia et al. (2002) and Schiavon et al. (2005), we construct a large database of Lick spectral indices for a total of 53 Galactic globular clusters with a wide range of metallicities, -2.4 < [Fe/H] < 0.1, and various horizontal-branch morphologies. The empirical index-to-metallicity conversion relationships are provided for the 20 Lick indices for the use of deriving meta…
We take a closer look at our published results of determination of ages, metallicities, helium mass fractions and abundances of chemical elements in Galactic globular clusters in order to find possible signatures of the phenomenon of multiple stellar populations in these data. Our analysis reveals that carbon abundances in the atmospheres of stars in the studied clusters change gradually during their evolution. The changes of the helium mass fraction and C, O, Mg and Na abundance anomalies caused by the effect of multiple stellar populations on the analyzed integrated-light spectra are detecte…
We present the results of determination of the age, helium mass fraction (Y) in terms of the used stellar evolutionary models, metallicity ([Fe/H]), and abundances of the elements C, O, Na, Mg, Ca, Ti, Cr and Mn for 26 globular clusters of the Galaxy. In this work, we apply a method developed by us that employs medium-resolution integrated-light spectra of globular clusters and models of stellar atmospheres and it is supplemented in this paper by the automatic calculation of microturbulence velocities of stars in the studied objects. Based on the data obtained for 26 objects, as well as on the…
The study of ages, helium mass fraction (Y) and chemical composition of globular clusters in dwarf galaxies is important for understanding the physical conditions at the main evolutionary stages of the host galaxies and for constraining the build-up histories of large galaxies. We present the analysis of integrated-light spectra of 8 extragalactic and 20 Galactic globular clusters (GCs) using our population synthesis method. We calculate synthetic spectra of GCs according to the defined stellar mass functions using model atmospheres and stellar parameters ($[Fe/H]$, $T_{eff}$, and $log g$) set…
We present the WiFeS Atlas of Galactic Globular cluster Spectra, a library of integrated spectra of Milky Way and Local Group globular clusters. We used the WiFeS integral field spectrograph on the Australian National University 2.3 m telescope to observe the central regions of 64 Milky Way globular clusters and 22 globular clusters hosted by the Milky Way's low mass satellite galaxies. The spectra have wider wavelength coverage (3300 Å to 9050 Å) and higher spectral resolution (R = 6800) than existing spectral libraries of Milky Way globular clusters. By including Large and Small Magellanic C…
Chemical abundances are presented for 25 M31 globular clusters (GCs), based on moderately high resolution (R = 22, 500) H-band integrated light spectra from the Apache Point Observatory Galactic Evolution Experiment (APOGEE). Infrared spectra offer lines from new elements, of different strengths, and at higher excitation potentials compared to the optical. Integrated abundances of C, N, and O are derived from CO, CN, and OH molecular features, while Fe, Na, Mg, Al, Si, K, Ca, and Ti abundances are derived from atomic features. These abundances are compared to previous results from the optical,…
We report the confirmation of an old, metal-poor globular cluster in the nearby dwarf irregular galaxy Sextans A, the first globular cluster known in this galaxy. The cluster, which we designate as Sextans A-GC1, lies some 4.4 arcminutes ($\sim1.8$ kpc) to the SW of the galaxy centre and clearly resolves into stars in sub-arcsecond seeing ground-based imaging.We measure an integrated magnitude $V=18.04$, corresponding to an absolute magnitude, $M_{V,0} = -7.85$. This gives an inferred mass $M\sim$1.6$\times10^5~M\odot$, assuming a Kroupa IMF. An integrated spectrum of Sextans A-GC1 reveals a h…
The results of determining the metallicity, age, helium mass fraction (Y) and abundances of the elements C, N, Mg, Ca, Mn, Ti and Cr by moderate resolution spectra for four globular clusters in the galaxy M 31: Bol 6, Bol 20, Bol 45 and Bol 50 are presented. The chemical composition for Bol 20 and Bol 50, and Y for four clusters are determined for the first time. The spectra of the studied objects were obtained with the 6-meter telescope of the SAO RAS in 2020. All the clusters under study turned out to be older than 11 Gyrs. The determined metallicities [Fe/H] are in the range from -1.1 to -0…
Spectrum Syntheses of High Resolution Integrated Light Spectra of Galactic Globular Clusters
本文给出了银河系球状星团47 Tuc、M3、M13、NGC 7006和M15的高分辨积分光谱中Mg、Na和Eu三种元素的光谱合成，以及太阳和大角星光谱的定标合成。铁丰度的目标集群也来自集成光等效宽度分析。在仔细考虑原子和分子光谱特征后，这五个球状星团光谱中的线轮廓非常合适，提供的精度水平优于相同积分光谱的等效宽度分析，并且与单个恒星分析的精度相当。来自5528和5711 A Mg I线、6154和6160 A Na I线以及6645 A Eu II线的积分光丰度落在单个恒星的观测范围内;然而，这些积分光丰度并不总是与文献中的平均丰度一致。用第二个参数簇M3、M13和NGC 7006进行的测试表明，假设不正确的水平分支形态可能对这些Mg、Na和Eu丰度只有很小的影响（< 0.06 dex）。因此，这些测试表明，集成的光谱合成可以应用于未解决的球状星团在很宽的范围内的金属丰度和水平分支形态。这种高精度的综合光谱合成对于解释其他星系周围球状星团系统的化学丰度是有价值的。
Evidence that the multiple populations (MPs) are common properties of globular clusters (GCs) is accumulated over the past decades from clusters in the Milky Way and in its satellites. This finding has revived GC research, and suggested that their formation at high redshift must have been a much-more complex phenomenon than imagined before. However, most information on MPs is limited to nearby GCs. The main limitation is that most studies on MPs rely on resolved stars, facing a major challenge to investigate the MP phenomenon in distant galaxies. Here we search for integrated colors of old GCs…
Globular clusters in \textsc{OrbIT}: complete dynamical characterisation of the globular cluster population of the Milky Way through updated orbital reconstruction
Università degli Studi di Bologna（博洛尼亚大学）；INAF（意大利国家天体物理研究所）；Pontificia Universidad Católica de Chile（智利天主教 Pontificia 大学）；Instituto Milenio de Astrofísica MAS（MAS 天体物理研究所）；Université Côte d’Azur（蔚蓝海岸大学）；Observatoire de la Côte d’Azur（蔚蓝海岸天文台）
We compare the results on the chemical composition of four globular clusters (GCs) in M31 (Bol 6, Bol 20, Bol 45, and Bol 50) (Maricheva M. 2021). Study of integrated spectra of four globular clusters in M31. Astrophys. Bull. 76:389-404. doi: https://doi.org/10.1134/S199034132104009X) to the available literature data on integrated-light spectroscopy of GCs with similar ages and chemical abundances in our Galaxy and M31 and on the chemical abundances of stars in two galaxies. The clusters and their literature analogues are of moderate metallicity -1.1<[Fe/H]<-0.75 dex and old (10 Gyr). Mg, Ca, …
We present a preliminary analysis of the effect of dynamical friction on the orbits of part of the globular clusters in our Galaxy. Our study considers an anisotropic velocity dispersion field approximated using the results of studies in the literature. An axisymmetric Galactic model with mass components consisting of a disc, a bulge, and a dark halo is employed in the computations. We provide a method to compute the dynamical friction acceleration in ellipsoidal, oblate, and prolate velocity distribution functions with similar density in velocity space. Orbital properties, such as mean time-v…
Integrated spectra of Milky Way globular clusters (GCs) are reproduced by computing synthetic spectra taking into account individual element abundances. Five clusters were selected from their location in the Galactic bulge, for which integrated spectra were available in the WiFeS Atlas of Galactic Globular Cluster Spectra project. Our aim is to further study the oldest GC located in the Galactic bulge, with metallicity in the range $-$1.6$<$[Fe/H]$<$$-$0.7. We also include the halo cluster NGC 6752 for comparison purposes. We reproduce the full spectra in the range 4500-9000 $\mathring{A}$ ava…
The ultra-diffuse galaxy NGC 1052-DF2 has an overabundance of luminous globular clusters (GCs), and its kinematics is consistent with the presence of little to no dark matter. As the velocity dispersion among the GCs is comparable to the expected internal dispersions of the individual GCs, the galaxy might be highly conducive to GC-GC merging. If true, this could explain the puzzling luminosity function of its GCs. Here, we examine this possibility by re-simulating three of our earlier simulations of the GC system (Dutta Chowdhury et al. 2019), where the GCs were modeled as single particles, w…
Binary stars as dynamical tracers in globular clusters .II. Evolution of the radial distribution of the binary star fraction
Indiana University（印第安纳大学）；INAF – Astrophysics and Space Science Observatory of Bologna（意大利国家天体物理研究所博洛尼亚天文与空间科学观测站）；University of Bologna（博洛尼亚大学）；European Southern Observatory（欧洲南方天文台）
We investigate the multiple stellar populations of the globular clusters M3, M5, M13, and M71 using $g^\prime$ and intermediate-band CN-$λ3883$ photometry obtained with the WIYN 0.9-m telescope on Kitt Peak. We find a strong correlation between red giant stars' CN$-g^\prime$ colors and their spectroscopic sodium abundances, thus demonstrating the efficacy of the two-filter system for stellar population studies. In all four clusters, the observed spread in red giant branch CN$-g^\prime$ colors is wider than that expected from photometric uncertainty, confirming the well-known chemical inhomogen…
We present abundances of globular clusters in the Milky Way and Fornax from integrated light spectra. Our goal is to evaluate the consistency of the integrated light analysis relative to standard abundance analysis for individual stars in those same clusters. This sample includes an updated analysis of 7 clusters from our previous publications and results for 5 new clusters that expand the metallicity range over which our technique has been tested. We find that the [Fe/H] measured from integrated light spectra agrees to $\sim$0.1 dex for globular clusters with metallicities as high as [Fe/H]=$…
The leading method for the determination of relevant stellar population parameters of unresolved extragalactic Globular Clusters is through the study of their integrated spectroscopy, where Balmer line-strength indices are considered to be age sensitive. Previously, a splitting in the highly optimised spectral line-strength index H$β_o$ was observed in a sample of Galactic globular clusters at all metallicities resulting in an apparent "upper branch" and "lower branch" of globular clusters in the H$β_o$ - [MgFe] diagram. This was suggested to be caused by the presence of hot Blue straggler sta…
The detection of intermediate mass black holes (IMBHs) in Galactic globular clusters (GCs) has so far been controversial. In order to characterize the effectiveness of integrated-light spectroscopy through integral field units, we analyze realistic mock data generated from state-of-the-art Monte Carlo simulations of GCs with a central IMBH, considering different setups and conditions varying IMBH mass, cluster distance, and accuracy in determination of the center. The mock observations are modeled with isotropic Jeans models to assess the success rate in identifying the IMBH presence, which we…
We have carried out a set of Monte Carlo simulations to study a number of fundamental aspects of the dynamical evolution of multiple stellar populations in globular clusters with different initial masses, fractions of second generation (2G) stars, and structural properties. Our simulations explore and elucidate: 1) the role of early and long-term dynamical processes and stellar escape in the evolution of the fraction of 2G stars and the link between the evolution of the fraction of 2G stars and various dynamical parameters; 2) the link between the fraction of 2G stars inside the cluster and in…
Sizeable number of stellar-mass black holes (BHs) in globular clusters (GCs) can strongly influence the dynamical evolution and observational properties of their host cluster. Using results from a large set of numerical simulations, we identify the key ingredients needed to sustain a sizeable population of BHs in GCs up to a Hubble time. We find that while BH natal kick prescriptions are essential in determining the initial retention fraction of BHs in GCs, the long-term survival of BHs is determined by the size, initial central density and half-mass relaxation time of the GC. Simulated GC mod…
The photometric properties that we could observe for Extra-Galactic Globular Clusters (EGGCs) are the integrated light of the system and for nearby EGGCs it also is possible to measure both half-light radii and the color spatial distribution, e.g. for areas smaller and larger than the half-light radius. No information about the internal dynamical state of the system could be directly obtained from observations. On the other hand, simulations of Globular Clusters (GCs) can provide detailed information about the dynamical evolution of the system. We present a preliminary study of EGGCs' photomet…
The morphology of thin stellar streams can be used to test the nature of dark matter. It is therefore crucial to extend searches for globular cluster streams to other galaxies than the Milky Way. In this paper, we investigate the current and future prospects of detecting globular cluster streams in external galaxies in resolved stars (e.g. with WFIRST) and using integrated light (e.g. with HSC, LSST and Euclid). In particular, we inject mock-streams to data from the PAndAS M31 survey, and produce simulated M31 backgrounds mimicking what WFIRST will observe in M31. Additionally, we estimate the…
This paper presents [Fe/H] ratios for GCs in the outer halo of the Andromeda Galaxy, M31, based on moderate-resolution, integrated light (IL) spectroscopy of the calcium-II triplet (CaT) lines. The CaT strengths are measured by fitting Voigt profiles to the lines and integrating those profiles; integrations of defined bandpasses are also considered. The [Fe/H] ratios are determined using an empirical calibration with CaT line strength, as derived from another sample of M31 GCs that were previously studied at high-resolution. The [Fe/H] ratios for the new GCs reveal that the outer halo GCs are …
Globular clusters of the Gaia Enceladus/Sausage -- I. Orbital and dynamical evolution on cosmological timescales
Main Astronomical Observatory, National Academy of Sciences of Ukraine（乌克兰国家科学院主天文台）；Nicolaus Copernicus Astronomical Centre Polish Academy of Sciences（波兰科学院尼古拉·哥白尼天文学中心）；Fesenkov Astrophysical Institute（费森科夫天体物理研究所）
This work reports the detection of a multi peaked colour pattern in the integrated colours distribution of globular clusters associated to the giant elliptical galaxy NGC 4486, using Next Generation Virgo Survey data. This feature is imprinted on the well known bimodal colour distribution of these clusters. Remarkably, the pattern is similar to that found in previous works based on photometry from the HST Advanced Camera Virgo Survey, in less massive Virgo galaxies. This characteristic can be traced up to to 45 arcmin (217 Kpc) in galactocentric radius. This suggests that globular cluster form…
We study the effects of non-local thermodynamic equilibrium (NLTE) on the abundance analysis of barium, magnesium, and manganese from integrated light spectroscopy, as typically applied to the analysis of extra-galactic star clusters and galaxies. In this paper, our reference object is a synthetic simple stellar population (SSP) representing a mono-metallic alpha-enhanced globular cluster with the metallicity [Fe/H]=-2.0 and the age of 11 Gyr. We used the MULTI2.3 program to compute LTE and NLTE equivalent widths of spectral lines of Mg I, Mn I, and Ba II ions, which are commonly used in abund…
The parameter A+, defined as the area enclosed between the cumulative radial distribution of blue straggler stars (BSSs) and that of a reference population, is a powerful indicator of the level of BSS central segregation. As part of the Hubble Space Telescope UV Legacy Survey of Galactic globular clusters (GCs), here we present the BSS population and the determination of A+ in 27 GCs observed out to about one half-mass radius. In combination with 21 additional clusters discussed in a previous paper this provides us with a global sample of 48 systems (corresponding to \sim 32\% of the Milky Way…
The formation and evolution of X-ray sources in globular clusters is likely to be affected by the cluster internal dynamics and the stellar interactions in the cluster dense environment.Several observational studies have revealed a correlation between the number of X-ray sources and the stellar encounter rate and provided evidence of the role of dynamics in the formation of X-ray binaries. We have performed a survey of Monte-Carlo simulations aimed at exploring the connection between the dynamics and formation of cataclysmic variables (CVs) and the origin of the observed correlation between th…
