scholarly journals Globular Cluster Candidates in the Sagittarius Dwarf Galaxy

2021 ◽  
Vol 162 (6) ◽  
pp. 261
Author(s):  
Andrés E. Piatti
Keyword(s):  
Galaxy Formation ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Open Cluster ◽  
Physical Reality ◽  
Star Formation History ◽  
Cluster Membership ◽  
Wide Range

Abstract Recently, new Sagittarius (Sgr) dwarf-galaxy globular clusters were discovered, which opens the question of the actual size of the Sgr globular cluster population, and therefore on our understanding of the Sgr galaxy formation and accretion history of the Milky Way. Based on Gaia EDR3 and SDSS IV DR16 (APOGEE-2) data sets, we performed an analysis of the color–magnitude diagrams (CMDs) of the eight new Sgr globular clusters found by Minniti et al. from a sound cleaning of the contamination of Milky Way and Sgr field stars, complemented by available kinematic and metal abundance information. The cleaned CMDs and spatial stellar distibutions reveal the presence of stars with a wide range of cluster membership probabilities. Minni 332 turned out to be a younger (<9 Gyr) and more metal-rich ([M/H] ≳ −1.0 dex) globular cluster than M54, the nuclear Sgr globular cluster; as could also be the case of Minni 342, 348, and 349, although their results are less convincing. Minni 341 could be an open cluster candidate (age < 1 Gyr, [M/H] ∼ −0.3 dex), while the analyses of Minni 335, 343, and 344 did not allow us to confirm their physical reality. We also built the Sgr cluster frequency (CF) using available ages of the Sgr globular clusters and compared it with that obtained from the Sgr star formation history. Both CFs are in excellent agreement. However, the addition of eight new globular clusters with ages and metallicities distributed according to the Sgr age–metallicity relationship turns out in a remarkably different CF.

scholarly journals The [α/Fe]–[Fe/H] relation in the E-MOSAICS simulations: its connection to the birth place of globular clusters and the fraction of globular cluster field stars in the bulge

2019 ◽  
Vol 491 (3) ◽  
pp. 4012-4022 ◽  
Author(s):  
Meghan E Hughes ◽  
Joel L Pfeffer ◽  
Marie Martig ◽  
Marta Reina-Campos ◽  
Nate Bastian ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Element Abundances ◽  
Field Star ◽  
Wide Range ◽  
The Galaxy ◽  
High Fraction ◽  
The Difference

ABSTRACT The α-element abundances of the globular cluster (GC) and field star populations of galaxies encode information about the formation of each of these components. We use the E-MOSAICS cosmological simulations of ∼L* galaxies and their GCs to investigate the [α/Fe]–[Fe/H] distribution of field stars and GCs in 25 Milky Way–mass galaxies. The [α/Fe]–[Fe/H] distribution of GCs largely follows that of the field stars and can also therefore be used as tracers of the [α/Fe]–[Fe/H] evolution of the galaxy. Due to the difference in their star formation histories, GCs associated with stellar streams (i.e. which have recently been accreted) have systematically lower [α/Fe] at fixed [Fe/H]. Therefore, if a GC is observed to have low [α/Fe] for its [Fe/H] there is an increased possibility that this GC was accreted recently alongside a dwarf galaxy. There is a wide range of shapes for the field star [α/Fe]–[Fe/H] distribution, with a notable subset of galaxies exhibiting bimodal distributions, in which the high [α/Fe] sequence is mostly comprised of stars in the bulge, a high fraction of which are from disrupted GCs. We calculate the contribution of disrupted GCs to the bulge component of the 25 simulated galaxies and find values between 0.3 and 14 per cent, where this fraction correlates with the galaxy’s formation time. The upper range of these fractions is compatible with observationally inferred measurements for the Milky Way, suggesting that in this respect the Milky Way is not typical of L*galaxies, having experienced a phase of unusually rapid growth at early times.

scholarly journals Dynamics of Globular Cluster Systems

1983 ◽  
Vol 100 ◽  
pp. 359-364
Author(s):  
K. C. Freeman
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Cluster Formation ◽  
Active Phase ◽  
Chemical Abundance ◽  
Cluster Systems ◽  
Chemical Enrichment ◽  
Wide Range ◽  
The Galaxy

In the Milky Way, the globular clusters are all very old, and we are accustomed to think of them as the oldest objects in the Galaxy. The clusters cover a wide range of chemical abundance, from near solar down to about [Fe/H] ⋍ −2.3. However there are field stars with abundances significantly lower than −2.3 (eg Bond, 1980); this implies that the clusters formed during the active phase of chemical enrichment, with cluster formation beginning at a time when the enrichment processes were already well under way.

scholarly journals The Milky Way’s stellar streams and globular clusters do not align in a Vast Polar Structure

2020 ◽  
Vol 494 (1) ◽  
pp. 983-1001 ◽  
Author(s):  
Alexander H Riley ◽  
Louis E Strigari
Keyword(s):  
Galaxy Formation ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Data Sets ◽  
Open Problems ◽  
Polar Structure ◽  
Dark Energy Survey ◽  
Stellar Streams ◽  
Orbital Configuration

ABSTRACT There is increasing evidence that a substantial fraction of Milky Way satellite galaxies align in a rotationally supported plane of satellites, a rare configuration in cosmological simulations of galaxy formation. It has been suggested that other Milky Way substructures (namely young halo globular clusters and stellar/gaseous streams) similarly tend to align with this plane, accordingly dubbed the Vast Polar Structure (VPOS). Using systemic proper motions inferred from Gaia data, we find that globular cluster orbital poles are not clustered in the VPOS direction, though the population with the highest VPOS membership fraction is the young halo clusters (∼30 per cent). We additionally provide a current census of stellar streams, including new streams discovered using the Dark Energy Survey and Gaia data sets, and find that stellar stream normals are also not clustered in the direction of the VPOS normal. We also find that, based on orbit modelling, there is a likely association between NGC 3201 and the Gjöll stellar stream and that, based on its orbital pole, NGC 4147 is likely not a Sagittarius globular cluster. That the Milky Way’s accreted globular clusters and streams do not align in the same planar configuration as its satellites suggests that the plane of satellites is either a particularly stable orbital configuration or a population of recently accreted satellites. Neither of these explanations is particularly likely in light of other recent studies, leaving the plane of satellites problem as one of the more consequential open problems in galaxy formation and cosmology.

scholarly journals The pristine dwarf-galaxy survey – III. Revealing the nature of the Milky Way globular cluster Sagittarius II

2021 ◽  
Vol 503 (2) ◽  
pp. 2754-2762
Author(s):  
Nicolas Longeard ◽  
Nicolas Martin ◽  
Rodrigo A Ibata ◽  
Else Starkenburg ◽  
Pascale Jablonka ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Confidence Limit ◽  
Globular Clusters ◽  
Milky Way ◽  
Velocity Dispersion ◽  
Dwarf Galaxy ◽  
Low Velocity ◽  
Data Set ◽  
Large Size ◽  
Additional Member

ABSTRACT We present a new spectroscopic study of the faint Milky Way satellite Sagittarius II. Using multiobject spectroscopy from the Fibre Large Array Multi-Element Spectrograph, we supplement the data set of Longeard et al. with 47 newly observed stars, 19 of which are identified as members of the satellite. These additional member stars are used to put tighter constraints on the dynamics and the metallicity properties of the system. We find a low velocity dispersion of $\sigma _\mathrm{v}^\mathrm{SgrII} = 1.7 \pm 0.5$ km s−1, in agreement with the dispersion of Milky Way globular clusters of similar luminosity. We confirm the very metal-poor nature of the satellite ([Fe/H]$_\mathrm{spectro}^\mathrm{SgrII} = -2.23 \pm 0.07$) and find that the metallicity dispersion of Sgr II is not resolved, reaching only 0.20 at the 95 per cent confidence limit. No star with a metallicity below −2.5 is confidently detected. Therefore, despite the unusually large size of the system (r$_h = 35.5 ^{+1.4}_{-1.2}$ pc), we conclude that Sgr II is an old and metal-poor globular cluster of the Milky Way.

scholarly journals Globular Cluster Streams as Galactic High-Precision Scales

2015 ◽  
Vol 11 (S317) ◽  
pp. 140-144
Author(s):  
Andreas H.W. Küpper ◽  
Eduardo Balbinot ◽  
Ana Bonaca ◽  
Kathryn V. Johnston ◽  
David W. Hogg ◽  
...  
Keyword(s):  
High Precision ◽  
Gravitational Potential ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Orbital Motion ◽  
Dwarf Galaxy ◽  
Tidal Streams

AbstractTidal streams of globular clusters are ideal tracers of the Galactic gravitational potential. Compared to the few known, complex and diffuse dwarf-galaxy streams, they are kinematically cold, have thin morphologies and are abundant in the halo of the Milky Way. Their coldness and thinness in combination with potential epicyclic substructure in the vicinity of the stream progenitor turns them into high-precision scales. With the example of Palomar 5, we demonstrate how modeling of a globular cluster stream allows us to simultaneously measure the properties of the disrupting globular cluster, its orbital motion, and the gravitational potential of the Milky Way.

scholarly journals The origin of globular cluster FSR 1758

2020 ◽  
Vol 635 ◽  
pp. A125
Author(s):  
Fu-Chi Yeh ◽  
Giovanni Carraro ◽  
Vladimir I. Korchagin ◽  
Camilla Pianta ◽  
Sergio Ortolani
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Initial Conditions ◽  
Dwarf Galaxy ◽  
Galactic Bulge ◽  
Orbital Parameters ◽  
Bulge Region ◽  
Analytical Time

Context. Globular clusters in the Milky Way are thought to have either an in situ origin, or to have been deposited in the Galaxy by past accretion events, like the spectacular Sagittarius dwarf galaxy merger. Aims. We probe the origin of the recently discovered globular cluster FSR 1758, often associated with some past merger event and which happens to be projected toward the Galactic bulge. We performed a detailed study of its Galactic orbit, and assign it to the most suitable Galactic component. Methods. We employed three different analytical time-independent potential models to calculate the orbit of the cluster by using the Gauss Radau spacings integration method. In addition, a time-dependent bar potential model is added to account for the influence of the Galactic bar. We ran a large suite of simulations via a Montecarlo method to account for the uncertainties in the initial conditions. Results. We confirm previous indications that the globular cluster FSR 1758 possesses a retrograde orbit with high eccentricity. The comparative analysis of the orbital parameters of star clusters in the Milky Way, in tandem with recent metallicity estimates, allows us to conclude that FSR 1758 is indeed a Galactic bulge intruder. The cluster can therefore be considered an old metal-poor halo globular cluster formed in situ that is passing right now in the bulge region. Its properties, however, can be roughly accounted for by also assuming that the cluster is part of some stream of extra-Galactic origin. Conclusions. We conclude that assessing the origin, either Galactic or extra-galactic, of globular clusters is surely a tantalising task. In any case, by using an Occam’s razor argument, we tend to prefer an in situ origin for FSR 1758.

scholarly journals Evidence for two early accretion events that built the Milky Way stellar halo

2019 ◽  
Vol 488 (1) ◽  
pp. 1235-1247 ◽  
Author(s):  
G C Myeong ◽  
E Vasiliev ◽  
G Iorio ◽  
N W Evans ◽  
V Belokurov
Keyword(s):  
Globular Cluster ◽  
Total Mass ◽  
Globular Clusters ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
High Energy ◽  
Stellar Mass ◽  
Milky Way Galaxy ◽  
Stellar Halo ◽  
Chemical Evidence

AbstractThe Gaia Sausage is the major accretion event that built the stellar halo of the Milky Way galaxy. Here, we provide dynamical and chemical evidence for a second substantial accretion episode, distinct from the Gaia Sausage. The Sequoia Event provided the bulk of the high-energy retrograde stars in the stellar halo, as well as the recently discovered globular cluster FSR 1758. There are up to six further globular clusters, including ω Centauri, as well as many of the retrograde substructures in Myeong et al., associated with the progenitor dwarf galaxy, named the Sequoia. The stellar mass in the Sequoia galaxy is ∼5 × 10  M⊙ , whilst the total mass is ∼1010 M⊙ , as judged from abundance matching or from the total sum of the globular cluster mass. Although clearly less massive than the Sausage, the Sequoia has a distinct chemodynamical signature. The strongly retrograde Sequoia stars have a typical eccentricity of ∼0.6, whereas the Sausage stars have no clear net rotation and move on predominantly radial orbits. On average, the Sequoia stars have lower metallicity by ∼0.3 dex and higher abundance ratios as compared to the Sausage. We conjecture that the Sausage and the Sequoia galaxies may have been associated and accreted at a comparable epoch.

scholarly journals The SLUGGS survey: measuring globular cluster ages using both photometry and spectroscopy

2019 ◽  
Vol 490 (1) ◽  
pp. 491-501 ◽  
Author(s):  
Christopher Usher ◽  
Jean P Brodie ◽  
Duncan A Forbes ◽  
Aaron J Romanowsky ◽  
Jay Strader ◽  
...  
Keyword(s):  
Galaxy Formation ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Near Infrared ◽  
Milky Way ◽  
Cluster Formation ◽  
Optical Photometry ◽  
History Of ◽  
Natural Outcome ◽  
Using Data

ABSTRACT Globular cluster ages provide both an important test of models of globular cluster formation and a powerful method to constrain the assembly history of galaxies. Unfortunately, measuring the ages of unresolved old stellar populations has proven challenging. Here, we present a novel technique that combines optical photometry with metallicity constraints from near-infrared spectroscopy in order to measure ages. After testing the method on globular clusters in the Milky Way and its satellite galaxies, we apply our technique to three massive early-type galaxies using data from the SAGES Legacy Unifying Globulars and GalaxieS (SLUGGS) survey. The three SLUGGS galaxies and the Milky Way show dramatically different globular cluster age and metallicity distributions, with NGC 1407 and the Milky Way showing mostly old globular clusters, while NGC 3115 and NGC 3377 show a range of globular ages. This diversity implies different galaxy formation histories and that the globular cluster optical colour–metallicity relation is not universal as is commonly assumed in globular cluster studies. We find a correlation between the median age of the metal-rich globular cluster populations and the age of the field star populations, in line with models where globular cluster formation is a natural outcome of high-intensity star formation.

scholarly journals Chemodynamics of newly identified giants with a globular cluster like abundance patterns in the bulge, disc, and halo of the Milky Way

2019 ◽  
Vol 488 (2) ◽  
pp. 2864-2880 ◽  
Author(s):  
José G Fernández-Trincado ◽  
Timothy C Beers ◽  
Baitian Tang ◽  
Edmundo Moreno ◽  
Angeles Pérez-Villegas ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
First Generation ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Main Element ◽  
Chemical Abundances ◽  
Giant Stars ◽  
Halo Population ◽  
Process Elements

ABSTRACT The latest edition of the APOGEE-2/DR14 survey catalogue and the first Payne data release of APOGEE abundance determinations by Ting et al. are examined. We identify 31 previously unremarked metal-poor giant stars with anomalously high levels of [N/Fe] abundances, which is not usually observed among metal-poor stars in the Milky Way. We made use of the Brussels Automatic Stellar Parameter (BACCHUS) code to re-derive manually the chemical abundances of 31 field stars in order to compile the main element families, namely the light elements (C, N), a-elements (O, Mg, Si), iron-peak element (Fe), s-process elements (Ce, Nd), and the light odd-Z element (Na, Al). We have found all these objects have a [N/Fe] ≳ +0.5, and are thus identified here as nitrogen-rich stars. An orbital analysis of these objects revealed that a handful of them shares the orbital properties of the bar/bulge, and possibly linked to tidal debris of surviving globular clusters trapped into the bar component. Three of the 31 stars are actually halo interlopers into the bulge area, which suggests that halo contamination is not insignificant when studying N-rich stars found in the inner Galaxy, whereas the rest of the N-rich stars share orbital properties with the halo population. Most of the newly identified population exhibits chemistry similar to the so-called second-generation globular cluster stars (enriched in aluminum, [Al/Fe] ≳ +0.5), whereas a handful of them exhibit lower abundances of aluminum, [Al/Fe] &lt; +0.5, which are thought to be chemically associated with the first generation of stars, as seen in globular clusters, or compatible with origin from a tidally disrupted dwarf galaxy.

scholarly journals The X-ray emissivity of low-density stellar populations

2020 ◽  
Vol 492 (4) ◽  
pp. 5684-5708 ◽  
Author(s):  
C O Heinke ◽  
M G Ivanov ◽  
E W Koch ◽  
R Andrews ◽  
L Chomiuk ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Dwarf Galaxy ◽  
Open Cluster ◽  
Strong Dependence ◽  
Galaxy Cluster ◽  
Stellar Populations ◽  
Low Density ◽  
X Ray ◽  
X Ray Binaries

ABSTRACT The dynamical production of low-mass X-ray binaries and brighter cataclysmic variables (CVs) in dense globular clusters is well-established. We investigate how the X-ray emissivity of fainter X-ray binaries (principally CVs and coronally active binaries) varies between different environments. We compile calculations (largely from the literature) of the X-ray emissivity of old stellar populations, including open and globular clusters and several galaxies. We investigate three literature claims of unusual X-ray sources in low-density stellar populations. We show that a suggested quiescent neutron star in the open cluster NGC 6819 is a foreground M dwarf. We show that the suggested diffuse X-ray emission from an old nova shell in the globular cluster NGC 6366 is actually a background galaxy cluster. And we show that a suggested population of quiescent X-ray binaries in the Sculptor Dwarf Galaxy is mostly (perhaps entirely) background galaxies. We find that above densities of 104 M⊙ pc−3, the X-ray emissivity of globular clusters increases, due to dynamical production of X-ray emitting systems. Below this density, globular clusters have lower X-ray emissivity than the other populations, and we do not see a strong dependence of X-ray emissivity due to density effects. We find significant correlations between X-ray emissivity and binary fraction, metallicity, and density. Sampling these fits via bootstrap techniques gives less significant correlations, but confirms the effect of metallicity on low-density populations, and that of density on the full globular cluster sample.

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