scholarly journals The Pristine Survey – VIII. The metallicity distribution function of the Milky Way halo down to the extremely metal-poor regime

2020 ◽  
Vol 492 (4) ◽  
pp. 4986-5002 ◽  
Author(s):  
K Youakim ◽  
E Starkenburg ◽  
N F Martin ◽  
G Matijevič ◽  
D S Aguado ◽  
...  
Keyword(s):  
Distribution Function ◽  
Globular Clusters ◽  
Milky Way ◽  
Current Data ◽  
Low Latitude ◽  
Chemical Enrichment ◽  
Merger Event ◽  
Low Metallicity ◽  
Metallicity Distribution ◽  
Milky Way Halo

ABSTRACT The Pristine survey uses narrow-band photometry to derive precise metallicities down to the extremely metal-poor regime ($ \rm [Fe/H] \lt -3$), and currently consists of over 4 million FGK-type stars over a sky area of $\sim 2500\, \mathrm{deg}^2$. We focus our analysis on a subsample of ∼80 000 main-sequence turn-off stars with heliocentric distances between 6 and 20 kpc, which we take to be a representative sample of the inner halo. The resulting metallicity distribution function (MDF) has a peak at $ \rm [Fe/H] =-1.6$, and a slope of Δ(LogN)/$\Delta \rm [Fe/H] = 1.0 \pm 0.1$ in the metallicity range of $-3.4\; \lt\; \rm [Fe/H]\; \lt -2.5$. This agrees well with a simple closed-box chemical enrichment model in this range, but is shallower than previous spectroscopic MDFs presented in the literature, suggesting that there may be a larger proportion of metal-poor stars in the inner halo than previously reported. We identify the Monoceros/TriAnd/ACS/EBS/A13 structure in metallicity space in a low-latitude field in the anticentre direction, and also discuss the possibility that the inner halo is dominated by a single, large merger event, but cannot strongly support or refute this idea with the current data. Finally, based on the MDF of field stars, we estimate the number of expected metal-poor globular clusters in the Milky Way halo to be 5.4 for $ \rm [Fe/H]\; \lt\; -2.5$ and 1.5 for $ \rm [Fe/H]\; \lt\; -3$, suggesting that the lack of low-metallicity globular clusters in the Milky Way is not due simply to statistical undersampling.

scholarly journals Reverse engineering the Milky Way

2020 ◽  
Vol 493 (1) ◽  
pp. 847-854 ◽  
Author(s):  
Duncan A Forbes
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Stellar Mass ◽  
Ex Situ ◽  
Scaling Relations ◽  
Integrals Of Motion ◽  
Chemical Enrichment ◽  
Effective Yield ◽  
Metallicity Distribution

ABSTRACT The ages, metallicities, alpha-elements, and integrals of motion of globular clusters (GCs) accreted by the Milky Way from disrupted satellites remain largely unchanged over time. Here we have used these conserved properties in combination to assign 76 GCs to five progenitor satellite galaxies – one of which we dub the Koala dwarf galaxy. We fit a leaky-box chemical enrichment model to the age–metallicity distribution of GCs, deriving the effective yield and the formation epoch of each satellite. Based on scaling relations of GC counts we estimate the original halo mass, stellar mass, and mean metallicity of each satellite. The total stellar mass of the five accreted satellites contributed around 109 M⊙ in stars to the growth of the Milky Way but over 50 per cent of the Milky Way’s GC system. The five satellites formed at very early times and were likely accreted 8–11 Gyr ago, indicating rapid growth for the Milky Way in its early evolution. We suggest that at least three satellites were originally nucleated, with the remnant nucleus now a GC of the Milky Way. 11 GCs are also identified as having formed ex situ but could not be assigned to a single progenitor satellite.

scholarly journals Neutron-capture elements in dwarf galaxies

2020 ◽  
Vol 634 ◽  
pp. A84 ◽  
Author(s):  
Á. Skúladóttir ◽  
C. J. Hansen ◽  
A. Choplin ◽  
S. Salvadori ◽  
M. Hampel ◽  
...  
Keyword(s):  
Massive Star ◽  
Milky Way ◽  
Dwarf Galaxies ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Chemical Enrichment ◽  
Theoretical Predictions ◽  
Low Metallicity ◽  
First Time ◽  
Best Fit

The slow (s) and intermediate (i) neutron (n) capture processes occur both in asymptotic giant branch (AGB) stars, and in massive stars. To study the build-up of the s- and i-products at low metallicity, we investigate the abundances of Y, Ba, La, Nd, and Eu in 98 stars, at −2.4 <  [Fe/H] <  −0.9, in the Sculptor dwarf spheroidal galaxy. The chemical enrichment from AGB stars becomes apparent at [Fe/H] ≈ −2 in Sculptor, and causes [Y/Ba], [La/Ba], [Nd/Ba] and [Eu/Ba] to decrease with metallicity, reaching subsolar values at the highest [Fe/H] ≈ −1. To investigate individual nucleosynthetic sites, we compared three n-rich Sculptor stars with theoretical yields. One carbon-enhanced metal-poor (CEMP-no) star with high [Sr, Y, Zr] >  +0.7 is best fit with a model of a rapidly-rotating massive star, the second (likely CH star) with the i-process, while the third has no satisfactory fit. For a more general understanding of the build-up of the heavy elements, we calculate for the first time the cumulative contribution of the s- and i-processes to the chemical enrichment in Sculptor, and compare with theoretical predictions. By correcting for the r-process, we derive [Y/Ba]s/i = −0.85 ± 0.16, [La/Ba]s/i = −0.49 ± 0.17, and [Nd/Ba]s/i = −0.48 ± 0.12, in the overall s- and/or i-process in Sculptor. These abundance ratios are within the range of those of CEMP stars in the Milky Way, which have either s- or i-process signatures. The low [Y/Ba]s/i and [La/Ba]s/i that we measure in Sculptor are inconsistent with them arising from the s-process only, but are more compatible with models of the i-process. Thus we conclude that both the s- and i-processes were important for the build-up of n-capture elements in the Sculptor dwarf spheroidal galaxy.

scholarly journals An ancient double degenerate merger in the Milky Way halo

2019 ◽  
Author(s):  
Adela Kawka ◽  
Stéphane Vennes ◽  
Lilia Ferrario
Keyword(s):  
White Dwarf ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Red Shift ◽  
High Mass ◽  
Retrograde Orbit ◽  
Merger Event ◽  
Whole Class ◽  
Milky Way Halo

Abstract We present an analysis and re-appraisal of the massive, carbon-enriched (DQ) white dwarf (WD) LP 93-21. Its high mass (≈1 M⊙) and membership to the class of warm DQ WDs, combined with its peculiar halo kinematics suggest that this object is the product of an ancient stellar merger event, most likely that of two WDs. Furthermore, the kinematics places this object on a highly retrograde orbit driven by the accretion of a dwarf galaxy onto the Milky Way that occurred at a red shift greater than 1.5. As the product of a stellar merger LP 93-21 is probably representative of the whole class of warm/hot DQ WDs.

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.

The Metallicity Distribution Function of Halo Dwarfs and Globular Clusters

1988 ◽  
Vol 126 ◽  
pp. 517-518
Author(s):  
J. B. Laird ◽  
M. P. Rupin ◽  
B. W. Carney ◽  
D. W. Latham ◽  
R. L. Kurucz
Keyword(s):  
Distribution Function ◽  
Simple Model ◽  
Chemical Evolution ◽  
Globular Clusters ◽  
Dwarf Stars ◽  
Metallicity Distribution

Metallicities have been determined for a chemically unbiased sample of field halo dwarf stars. Their metallicity distribution function is similar to the predictions of a simple model of chemical evolution, but somewhat different from that of globular clusters.

Globular clusters and their link with stellar populations in the Milky Way

2019 ◽  
Vol 14 (S351) ◽  
pp. 19-23
Author(s):  
David Yong
Keyword(s):  
Chemical Evolution ◽  
Globular Clusters ◽  
Milky Way ◽  
Star Clusters ◽  
Stellar Populations ◽  
Chemical Compositions ◽  
Chemical Abundance ◽  
Chemical Enrichment ◽  
Similarities And Differences ◽  
Insight Into

AbstractObservations of stellar chemical compositions enable us to identify connections between globular clusters and stellar populations in the Milky Way. In particular, chemical abundance ratios provide detailed insight into the chemical enrichment histories of star clusters and the field populations. For some elements, there are striking differences between field and cluster stars which reflect different nucleosynthetic processes and/or chemical evolution. The goal of this talk was to provide an overview of similarities and differences in chemical compositions between globular clusters and the Milky Way as well as highlighting a few areas for further examination.

scholarly journals GMOS Spectroscopy of Globular Clusters in Dwarf Elliptical Galaxies

2007 ◽  
Vol 3 (S246) ◽  
pp. 429-430
Author(s):  
Bryan W. Miller ◽  
Jennifer Lotz ◽  
Michael Hilker ◽  
Markus Kissler-Patig ◽  
Thomas Puzia
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Elliptical Galaxies ◽  
Preliminary Results ◽  
Dwarf Elliptical Galaxies ◽  
Milky Way Halo

AbstractWe present a Gemini/GMOS program to measure spectroscopic metallicities and ages of globular clusters (GCs) and nuclei in dwarf elliptical galaxies in the Virgo and Fornax Clusters. Preliminary results indicate that the globular clusters are old and metal-poor, very similar to the GCs in the Milky Way halo. The nuclei tend to be more metal-rich than the globular clusters but more metal-poor and older, on average, than the stars in the bodies of the galaxies. The [α/Fe] ratio appears to be solar for the GCs, nuclei, and dEs, but the uncertainties do not exclude some globular clusters from being enhanced in alpha elements.

scholarly journals Kinematics of outer halo globular clusters: M 75 and NGC 6426

2018 ◽  
Vol 616 ◽  
pp. A74 ◽  
Author(s):  
Andreas Koch ◽  
Michael Hanke ◽  
Nikolay Kacharov
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
High Resolution Spectroscopy ◽  
Large Uncertainty ◽  
Dynamic Interactions ◽  
A Value ◽  
Kinematic Study ◽  
Younger Age ◽  
Low Metallicity ◽  
Insight Into

Globular clusters (GCs) and their dynamic interactions with the Galactic components provide an important insight into the structure and formation of the early Milky Way. We present a kinematic study of two outer halo GCs based on a combination of VLT/FORS2, VLT/FLAMES, and Magellan/MIKE low- and high-resolution spectroscopy of 32 and 27 member stars, respectively. Although both clusters are located at Galactocentric distances of 15 kpc, they have otherwise very different properties. M 75 is a luminous and metal-rich system at [Fe/H] = −1.2 dex, which is a value that we confirm from the calcium triplet region. This GC shows mild evidence for rotation with an amplitude of Arot ~ 5 km s−1. One of the most metal-poor GCs in the Milky Way (at [Fe II/H] = −2.3 dex), NGC 6426 exhibits marginal evidence of internal rotation at the 2 km s−1 level. Both objects have velocity dispersions that are consistent with their luminosity. Although limited by small-number statistics, the resulting limits on their Arot/σ0 ratios suggest that M 75 is a slow rotator driven by internal dynamics rather than being affected by the weak Galactic tides at its large distances. In this work, M 75 (Arot/σ0 = 0.31) is fully consistent with the properties of other, younger halo clusters. At Arot/σ0 = 0.8 ± 0.4, NGC 6426 appears to have a remarkably ordered internal motion for its low metallicity, but the large uncertainty does not allow for an unambiguous categorization as a fast rotator. An accretion origin of M 75 cannot be excluded, based on the eccentric orbit, which we derived from the recent data release 2 of Gaia, and considering its younger age.

scholarly journals The Metallicity Distribution Function of the Halo of the Milky Way

2005 ◽  
Vol 1 (S228) ◽  
pp. 175-183 ◽  
Author(s):  
Timothy C. Beers ◽  
Norbert Christlieb ◽  
John E. Norris ◽  
Michael S. Bessell ◽  
Ronald Wilhelm ◽  
...  
Keyword(s):  
Distribution Function ◽  
Milky Way ◽  
Metallicity Distribution

scholarly journals Complexity in small-scale dwarf spheroidal galaxies

2009 ◽  
Vol 5 (S265) ◽  
pp. 227-232
Author(s):  
Andreas Koch ◽  
Daniel Adén ◽  
Eva K. Grebel ◽  
Sofia Feltzing
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Galactic Halo ◽  
Photometric Data ◽  
Small Scale ◽  
Chemical Abundance ◽  
First Stars ◽  
Dwarf Spheroidal Galaxies ◽  
Chemical Enrichment ◽  
Large Numbers

AbstractOur knowledge about the chemical evolution of the more luminous dwarf spheroidal (dSph) galaxies is constantly growing. However, little is known about the enrichment of the ultrafaint systems recently discovered in large numbers in large Sky Surveys. Low-resolution spectroscopy and photometric data indicate that these galaxies are predominantly metal-poor. On the other hand, the most recent high-resolution abundance analyses indicate that some of these galaxies experienced highly inhomogenous chemical enrichment, where star formation proceeds locally on the smallest scales. Furthermore, these galaxy-contenders appear to contain very metal-poor stars with [Fe/H]< −3 dex and could be the sites of the first stars. Here, we consider the presently available chemical abundance information of the (ultra-) faint Milky Way satellite dSphs. In this context, some of the most peculiar element and inhomogeneous enrichment patterns will be discussed and related to the question of to what extent the faintest dSph candidates and outer halo globular clusters could have contributed to the metal-poor Galactic halo.

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