scholarly journals Rediscovering the origins of the stellar halo with chemical tagging

2017 ◽  
Vol 13 (S334) ◽  
pp. 38-42 ◽  
Author(s):  
Sarah L Martell
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Galactic Halo ◽  
Light Element ◽  
Element Abundance ◽  
Tidal Interactions ◽  
Halo Stars ◽  
The Galaxy ◽  
Stellar Halo ◽  
Light Element Abundance

AbstractThe Galactic halo has a complex assembly history, which can be seen in its wealth of kinematic and chemical substructure. Globular clusters lose stars through tidal interactions with the Galaxy and cluster evaporation processes, meaning that they are inevitably a source of halo stars. These “migrants” from globular clusters can be recognized in the halo field by the characteristic light element abundance anticorrelations that are commonly observed only in globular cluster stars, and the number of halo stars that can be chemically tagged to globular clusters can be used to place limits on the formation pathways of those clusters.

scholarly journals The mass fraction of halo stars contributed by the disruption of globular clusters in the E-MOSAICS simulations

2020 ◽  
Vol 493 (3) ◽  
pp. 3422-3428 ◽  
Author(s):  
Marta Reina-Campos ◽  
Meghan E Hughes ◽  
J M Diederik Kruijssen ◽  
Joel L Pfeffer ◽  
Nate Bastian ◽  
...  
Keyword(s):  
Mass Fraction ◽  
Globular Clusters ◽  
Milky Way ◽  
Galactic Halo ◽  
Light Element ◽  
Element Abundance ◽  
Host Galaxies ◽  
Stellar Cluster ◽  
Halo Stars ◽  
Stellar Halo

ABSTRACT Globular clusters (GCs) have been posited, alongside dwarf galaxies, as significant contributors to the field stellar population of the Galactic halo. In order to quantify their contribution, we examine the fraction of halo stars formed in stellar clusters in the suite of 25 present-day Milky Way-mass cosmological zoom simulations from the E-MOSAICS project. We find that a median of 2.3 and 0.3 per cent of the mass in halo field stars formed in clusters and GCs, defined as clusters more massive than 5 × 103 and 105 M⊙, respectively, with the 25–75th percentiles spanning 1.9–3.0 and 0.2–0.5 per cent being caused by differences in the assembly histories of the host galaxies. Under the extreme assumption that no stellar cluster survives to the present day, the mass fractions increase to a median of 5.9 and 1.8 per cent. These small fractions indicate that the disruption of GCs plays a subdominant role in the build-up of the stellar halo. We also determine the contributed halo mass fraction that would present signatures of light-element abundance variations considered to be unique to GCs, and find that clusters and GCs would contribute a median of 1.1 and 0.2 per cent, respectively. We estimate the contributed fraction of GC stars to the Milky Way halo, based on recent surveys, and find upper limits of 2–5 per cent (significantly lower than previous estimates), suggesting that models other than those invoking strong mass loss are required to describe the formation of chemically enriched stellar populations in GCs.

scholarly journals Purveyors of fine halos: Re-assessing globular cluster contributions to the Milky Way halo buildup with SDSS-IV

2019 ◽  
Vol 625 ◽  
pp. A75 ◽  
Author(s):  
Andreas Koch ◽  
Eva K. Grebel ◽  
Sarah L. Martell
Keyword(s):  
Globular Cluster ◽  
First Generation ◽  
Second Generation ◽  
Milky Way ◽  
Galactic Halo ◽  
Light Element ◽  
Ex Situ ◽  
Element Abundance ◽  
Ample Evidence ◽  
Halo Stars

There is ample evidence in the Milky Way for globular cluster (GC) disruption. It may therefore be expected that part of the Galactic halo field star population may also once have formed in GCs. We seek to quantify the fraction of halo stars donated by GCs by searching for stars that bear the unique chemical fingerprints typical for a subset of GC stars often dubbed “second-generation stars”. These are stars showing light-element abundance anomalies such as a pronounced CN-band strength accompanied by weak CH-bands. Based on this indicator, past studies have placed the fraction of halo stars with a GC origin between a few to up to 50%. Using low-resolution spectra from the most recent data release (DR14) of the latest extension of the Sloan Digital Sky Survey (SDSS-IV), we were able to identify 118 metal-poor (−1.8 ≤ [Fe/H] ≤ −1.3) CN-strong stars in a sample of 4470 halo giant stars out to ∼50 kpc. This increases the number of known halo stars with GC-like light-element abundances by a factor of two and results in an observed fraction of these stars of 2.6 ± 0.2%. Using an updated formalism to account for the fraction of stars lost early on in the GC evolution, we thus estimate the fraction of the Galactic halo that stems from disrupted clusters to be very low, at 11 ± 1%. This number would represent the case that stars lost from GCs were entirely from the first generation and is thus merely an upper limit. Our conclusions are sensitive to our assumptions of the mass lost early on from the first generation formed in the GCs, the ratio of first-to-second generation stars, and other GC parameters. We carefully tested the influence of varying these parameters on the final result and find that under realistic scenarios, this fraction depends on the main assumptions at less than 10 percentage points. We further recover a flat trend in this fraction with Galactocentric radius, with a marginal indication of a rise beyond 30 kpc that could reflect the ex situ origin of the outer halo as is also seen in other stellar tracers.

scholarly journals Integrated spectroscopy of extragalactic Globular Clusters

2019 ◽  
Vol 14 (S351) ◽  
pp. 155-160
Author(s):  
Charli M. Sakari
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Light Element ◽  
Element Abundance ◽  
Future Perspectives ◽  
Host Galaxies ◽  
Chemical Abundances ◽  
Essential Information ◽  
Light Element Abundance ◽  
Detailed Chemical

AbstractIntegrated 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 perspectives, emphasizing how IL spectroscopy can bridge the gap between Galactic and extragalactic astronomy.

scholarly journals Multiple populations in integrated light spectroscopy of intermediate-age clusters

2019 ◽  
Vol 489 (1) ◽  
pp. L80-L85 ◽  
Author(s):  
Nate Bastian ◽  
Christopher Usher ◽  
Sebastian Kamann ◽  
Carmela Lardo ◽  
Søren S Larsen ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Light Element ◽  
Large Magellanic Cloud ◽  
Element Abundance ◽  
Multiple Populations ◽  
Individual Stars ◽  
Abundance Patterns ◽  
Nearby Galaxies ◽  
Massive Clusters ◽  
Light Element Abundance

ABSTRACT The presence of star-to-star light-element abundance variations (also known as multiple populations, MPs) appears to be ubiquitous within old and massive clusters in the Milky Way and all studied nearby galaxies. Most previous studies have focused on resolved images or spectroscopy of individual stars, although there has been significant effort in the past few years to look for multiple population signatures in integrated light spectroscopy. If proven feasible, integrated light studies offer a potential way to vastly open parameter space, as clusters out to 10s of Mpc can be studied. We use the Na D lines in the integrated spectra of two clusters with similar ages (2–3 Gyr) but very different masses: NGC 1978 (∼3 × 105 M⊙) in the Large Magellanic Cloud and G114 (1.7 × 107 M⊙) in NGC 1316. For NGC 1978, our findings agree with resolved studies of individual stars that did not find evidence for Na spreads. However, for G114, we find clear evidence for the presence of multiple populations. The fact that the same anomalous abundance patterns are found in both the intermediate age and ancient globular clusters lends further support to the notion that young massive clusters are effectively the same as the ancient globular clusters, only separated in age.

scholarly journals LIGHT-ELEMENT ABUNDANCE VARIATIONS AT LOW METALLICITY: THE GLOBULAR CLUSTER NGC 5466

2010 ◽  
Vol 140 (4) ◽  
pp. 1119-1127 ◽  
Author(s):  
Matthew Shetrone ◽  
Sarah L. Martell ◽  
Rachel Wilkerson ◽  
Joshua Adams ◽  
Michael H. Siegel ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Light Element ◽  
Element Abundance ◽  
Low Metallicity ◽  
Light Element Abundance

scholarly journals Observational signatures of lithium depletion in the metal-poor globular cluster NGC6397

2009 ◽  
Vol 5 (S268) ◽  
pp. 263-268 ◽  
Author(s):  
Karin Lind ◽  
Francesca Primas ◽  
Corinne Charbonnel ◽  
Frank Grundahl ◽  
Martin Asplund
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Main Sequence ◽  
Galactic Halo ◽  
Main Sequence Stars ◽  
Surface Evolution ◽  
Halo Stars ◽  
Systematic Uncertainties ◽  
Low Mass ◽  
Lithium Depletion

AbstractThe “stellar” solution to the cosmological lithium problem proposes that surface depletion of lithium in low-mass, metal-poor stars can reconcile the lower abundances found for Galactic halo stars with the primordial prediction. Globular clusters are ideal environments for studies of the surface evolution of lithium, with large number statistics possible to obtain for main sequence stars as well as giants. We discuss the Li abundances measured for >450 stars in the globular cluster NGC 6397, focusing on the evidence for lithium depletion and especially highlighting how the inferred abundances and interpretations are affected by early cluster self-enrichment and systematic uncertainties in the effective temperature determination.

The contribution of Globular Clusters to the stellar halo using APOGEE and GAIA

2019 ◽  
Vol 14 (S351) ◽  
pp. 455-459
Author(s):  
Danny Horta ◽  
J. Ted Mackereth ◽  
Ricardo P. Schiavon ◽  
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Substantial Fraction ◽  
Data Release ◽  
The Galaxy ◽  
Stellar Halo ◽  
Mass Assembly ◽  
Key Questions

AbstractOver the last decade, much of the key questions in Galactic Archaeology have been asnwered by studying the Milky Way’s globular cluster (GC) system. Following on this, it has been shown that a substantial fraction of the Milky Way’s stellar halo field arises from GC dissolution. In this work, we make use of the latest data release fromn the APOGEE survey to study GC dissolution ratios in different spatial regions of the Galaxy. Our results will allow us to constrain many astrophysical questions, such as: the origin of N-Rich stars, the mass contribution from GCs to the stellar halo of the Galaxy, the origin of the Galactic GC system and the mass assembly of the Milky Way.

scholarly journals Gaia DR2 orbital properties for field stars with globular cluster-like CN band strengths

2019 ◽  
Vol 624 ◽  
pp. L9 ◽  
Author(s):  
A. Savino ◽  
L. Posti
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Light Element ◽  
Small Population ◽  
Sloan Digital Sky Survey ◽  
Element Abundances ◽  
Halo Stars ◽  
Sky Survey ◽  
Gaia Dr2

Context. Large spectroscopic surveys of the Milky Way have revealed that a small population of stars in the halo have light element abundances comparable to those found in globular clusters. The favoured explanation for the peculiar abundances of these stars is that they originated inside a globular cluster and were subsequently lost. Aims. Using orbit calculations we assess the likelihood that an existing sample of 57 field stars with globular cluster-like CN band strength originated in any of the currently known Milky Way globular clusters. Methods. Using Sloan Digital Sky Survey and Gaia data, we determine orbits and integrals of motion of our sample of field stars, and use these values and metallicity to identify likely matches to globular clusters. The pivot hypothesis is that had these stars been stripped from such objects, they would have remained on very similar orbits. Results. We find that ∼70% of the sample of field stars have orbital properties consistent with the halo of the Milky Way; however, only 20 stars have likely orbital associations with an existing globular cluster. The remaining ∼30% of the sample have orbits that place them in the outer Galactic disc. No cluster of similar metallicity is known on analogous disc orbits. Conclusions. The orbital properties of the halo stars seem to be compatible with the globular cluster escapee scenario. The stars in the outer disc are particularly surprising and deserve further investigation to establish their nature.

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