Leveraging HST with MUSE – I. Sodium abundance variations within the 2-Gyr-old cluster NGC 1978

ABSTRACT Nearly all of the well-studied ancient globular clusters (GCs), in the Milky Way and in nearby galaxies, show star-to-star variations in specific elements (e.g. He, C, N, O, Na, and Al), known as ‘multiple populations’ (MPs). However, MPs are not restricted to ancient clusters, with massive clusters down to ∼2 Gyr showing signs of chemical variations. This suggests that young and old clusters share the same formation mechanism but most of the work to date on younger clusters has focused on N variations. Initial studies even suggested that younger clusters may not host spreads in other elements beyond N (e.g. Na), calling into question whether these abundance variations share the same origin as in the older GCs. In this work, we combine Hubble Space Telescope (HST) photometry with Very Large Telescope (VLT)/Multi-Unit Spectroscopic Explorer (MUSE) spectroscopy of a large sample of red giant branch (RGB) stars (338) in the Large Magellanic Cloud cluster NGC 1978, the youngest globular to date with reported MPs in the form of N spreads. By combining the spectra of individual RGB stars into N-normal and N-enhanced samples, based on the ‘chromosome map’ derived from HST, we search for mean abundance variations. Based on the NaD line, we find a Na difference of Δ[Na/Fe] = 0.07 ± 0.01 between the populations. While this difference is smaller than typically found in ancient GCs (which may suggest a correlation with age), this result further confirms that the MP phenomenon is the same, regardless of cluster age and host galaxy. As such, these young clusters offer some of the strictest tests for theories on the origin of MPs.

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Chromosome maps of young LMC clusters: an additional case of coeval multiple populations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa644 ◽

2020 ◽

Vol 493 (4) ◽

pp. 6060-6070 ◽

Cited By ~ 5

Author(s):

S Saracino ◽

S Martocchia ◽

N Bastian ◽

V Kozhurina-Platais ◽

W Chantereau ◽

...

Keyword(s):

Globular Clusters ◽

Hubble Space Telescope ◽

Large Magellanic Cloud ◽

Magellanic Cloud ◽

Host Galaxy ◽

Clear Correlation ◽

Age Difference ◽

Multiple Star ◽

Multiple Populations ◽

Red Giant

ABSTRACT Recent studies have revealed that the multiple populations (MPs) phenomenon does not occur only in ancient and massive Galactic globular clusters (GCs), but it is also observed in external galaxies, where GCs sample a wide age range with respect to the Milky Way. However, for a long time, it was unclear whether we were looking at the same phenomenon in different environments or not. The first evidence that the MPs phenomenon is the same regardless of cluster age and host galaxy came out recently, when an intermediate-age cluster from the Small Magellanic Cloud, Lindsay 1, and a Galactic GC have been directly compared. By complementing those data with new images from the Hubble Space Telescope (HST), we extend the comparison to two clusters of different ages: NGC 2121 (∼2.5 Gyr) and NGC 1783 (∼1.5 Gyr), from the Large Magellanic Cloud. We find a clear correlation between the RGB (red giant branch) width in the pseudo-colour CF275W, F343N, F438W and the age of the cluster itself, with the older cluster having larger σ(CF275W, F343N, F438W)RGB and vice versa. Unfortunately, the σ values cannot be directly linked to the N-abundance variations within the clusters before properly taking account the effect of the first dredge-up. Such HST data also allow us to explore whether multiple star formation episodes occurred within NGC 2121. The two populations are indistinguishable, with an age difference of only 6 ± 12 Myr and an initial helium spread of 0.02 or lower. This confirms our previous results, putting serious constraints on any model proposed to explain the origin of the chemical anomalies in GCs.

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An extragalactic chromosome map: the intermediate-age SMC cluster Lindsay 1

Monthly Notices of the Royal Astronomical Society Letters ◽

10.1093/mnrasl/slz135 ◽

2019 ◽

Vol 489 (1) ◽

pp. L97-L101 ◽

Cited By ~ 7

Author(s):

S Saracino ◽

N Bastian ◽

V Kozhurina-Platais ◽

I Cabrera-Ziri ◽

E Dalessandro ◽

...

Keyword(s):

Globular Clusters ◽

Hubble Space Telescope ◽

Unique Property ◽

Open Clusters ◽

Host Galaxy ◽

Lower Mass ◽

Chromosome Map ◽

Uv Photometry ◽

Massive Clusters ◽

Cluster Age

ABSTRACT The discovery of star-to-star abundance variations (a.k.a. multiple populations – MPs) within globular clusters (GCs), which are generally not found in the field or in lower mass open clusters, has led to a search for the unique property of GCs that allow them to host this phenomenon. Recent studies have shown that MPs are not limited to the ancient GCs but are also found in massive clusters with ages down to (at least) 2 Gyr. This finding is important for understanding the physics of the MP phenomenon, as these young clusters can provide much stronger constraints (e.g. on potential age spreads within the clusters) than older ones. However, a direct comparison between ancient GCs and intermediate clusters has not yet been possible due to the different filters adopted in their studies. Here we present new Hubble Space Telescope UV photometry of the 7.5 Gyr, massive Small Magellanic Cloud cluster, Lindsay 1, in order to compare its pseudo colour–colour diagram to that of Galactic GCs. We find that they are almost identical and conclude that the MPs phenomenon is the same, regardless of cluster age and host galaxy.

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Multiple populations in integrated light spectroscopy of intermediate-age clusters

Monthly Notices of the Royal Astronomical Society Letters ◽

10.1093/mnrasl/slz130 ◽

2019 ◽

Vol 489 (1) ◽

pp. L80-L85 ◽

Cited By ~ 4

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.

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Multiple Stellar Populations at Less-evolved Stages-II: No Evidence of Significant Helium Spread among NGC 1846 Dwarfs

The Astrophysical Journal ◽

10.3847/1538-4357/ac2059 ◽

2021 ◽

Vol 921 (2) ◽

pp. 171

Author(s):

Chengyuan Li

Keyword(s):

Globular Clusters ◽

Main Sequence ◽

Hubble Space Telescope ◽

Star Clusters ◽

Stellar Populations ◽

Color Variation ◽

Nitrogen Enrichment ◽

Main Sequence Stars ◽

Red Giant ◽

Cluster Age

Abstract The detection of star-to-star chemical variations in star clusters older than 2 Gyr has changed the traditional view of star clusters as canonical examples of “simple stellar populations” into the so-called “multiple stellar populations” (MPs). Although the significance of MPs seems to correlate with cluster total mass, it seems that the presence of MPs is determined by cluster age. In this article, we use deep photometry from the Hubble Space Telescope to investigate whether the FG-type dwarfs in the ∼1.7 Gyr old cluster NGC 1846, have helium spread. By comparing the observation with the synthetic stellar populations, we estimate a helium spread of ΔY ∼ 0.01 ± 0.01 among the main-sequence stars in NGC 1846. The maximum helium spread would not exceed ΔY ∼ 0.02, depending on the adopted fraction of helium-enriched stars. To mask the color variation caused by such a helium enrichment, a nitrogen enrichment of at least Δ[N/Fe] = 0.8 dex is required, which is excluded by previous analyses of the red-giant branch in this cluster. We find that our result is consistent with the ΔY–mass relationship for Galactic globular clusters. To examine whether or not NGC 1846 harbors MPs, higher photometric accuracy is required. We conclude that under the adopted photometric quality, there is no extreme helium variation among NGC 1846 dwarfs.

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The accreted nuclear clusters of the Milky Way

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3407 ◽

2020 ◽

Vol 500 (2) ◽

pp. 2514-2524

Author(s):

Joel Pfeffer ◽

Carmela Lardo ◽

Nate Bastian ◽

Sara Saracino ◽

Sebastian Kamann

Keyword(s):

Globular Clusters ◽

Milky Way ◽

Dwarf Galaxy ◽

Star Clusters ◽

Host Galaxy ◽

The Galaxy ◽

Nuclear Clusters ◽

The Common ◽

Massive Clusters ◽

Peculiar Case

ABSTRACT A number of the massive clusters in the halo, bulge, and disc of the Galaxy are not genuine globular clusters (GCs) but instead are different beasts altogether. They are the remnant nuclear star clusters (NSCs) of ancient galaxies since accreted by the Milky Way. While some clusters are readily identifiable as NSCs and can be readily traced back to their host galaxy (e.g. M54 and the Sagittarius Dwarf galaxy), others have proven more elusive. Here, we combine a number of independent constraints, focusing on their internal abundances and overall kinematics, to find NSCs accreted by the Galaxy and trace them to their accretion event. We find that the true NSCs accreted by the Galaxy are: M54 from the Sagittarius Dwarf, ω Centari from Gaia-Enceladus/Sausage, NGC 6273 from Kraken, and (potentially) NGC 6934 from the Helmi Streams. These NSCs are prime candidates for searches of intermediate-mass black holes (BHs) within star clusters, given the common occurrence of galaxies hosting both NSCs and central massive BHs. No NSC appears to be associated with Sequoia or other minor accretion events. Other claimed NSCs are shown not to be such. We also discuss the peculiar case of Terzan 5, which may represent a unique case of a cluster–cluster merger.

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UV-Observations of Young Populous Clusters in the Large Magellanic Cloud

Symposium - International Astronomical Union ◽

10.1017/s0074180900039929 ◽

1984 ◽

Vol 108 ◽

pp. 55-56

Author(s):

Edward H. Geyer ◽

Angelo Cassatella

Keyword(s):

Globular Clusters ◽

Main Sequence ◽

Large Magellanic Cloud ◽

Time Interval ◽

Sequence Evolution ◽

Stellar Clusters ◽

T Tauri ◽

Red Supergiants ◽

Evolution Phase ◽

Massive Clusters

The young populous star clusters give evidence for the ‘explosive’ star formation in the Magellanic Clouds which took place in the time interval 5·106 yrs to < 108 yrs agoe. They are also key objects for the understanding of the formation of massive stellar clusters, because they are still situated close to their ‘birthplace’ in the parent galaxy and are dynamically not relaxed (Geyer et al. 1979). Their HRD-morphology shows most of the member stars in the upper Main Sequence range with only a few massive yellow and red supergiants. The lower massive stars are still in the pre-main-sequence evolution phase (‘T-Tauri state’), which cannot be observed at the MC's distances. Thus in the uv-spectral range the blue stars with (B-V) < 0.1 on the upper MS contribute to the uv-fluxes. In the optical spectral regions the bright ‘blue’ globular clusters seem not be embedded in remanent interstellar matter, though neighbouring loose stellar aggregates of similar age are in many cases surrounded by dense HII-regions. This rises the questions wether the starformation process in such massive clusters was so efficient that no remanent matter was left over, or was this material blown away by the uv-radiation of the numerous OB-member stars?

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Lithium abundance in lower red giant branch stars of Omega Centauri

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833457 ◽

2018 ◽

Vol 618 ◽

pp. A134 ◽

Cited By ~ 5

Author(s):

A. Mucciarelli ◽

M. Salaris ◽

L. Monaco ◽

P. Bonifacio ◽

X. Fu ◽

...

Keyword(s):

High Resolution ◽

Globular Clusters ◽

Stellar System ◽

The Other ◽

Large Telescope ◽

Lithium Abundance ◽

Very Large Telescope ◽

Red Giant ◽

Giant Branch Stars ◽

Branch Star

We present Li, Na, Al, and Fe abundances of 199 lower red giant branch star members of the stellar system Omega Centauri, using high-resolution spectra acquired with FLAMES at the Very Large Telescope. The A(Li) distribution is peaked at A(Li) ∼ 1 dex with a prominent tail towards lower values. The peak of the distribution well agrees with the lithium abundances measured in lower red giant branch stars in globular clusters and Galactic field stars. Stars with A(Li) ∼ 1 dex are found at metallicities lower than [Fe/H] ∼ –1.3 dex but they disappear at higher metallicities. On the other hand, Li-poor stars are found at all metallicities. The most metal-poor stars exhibit a clear Li–Na anti-correlation, where about 30% of the sample have A(Li) lower than ∼0.8 dex, while these stars represent a small fraction of normal globular clusters. Most of the stars with [Fe/H] > –1.6 dex are Li poor and Na rich. The Li depletion measured in these stars is not observed in globular clusters with similar metallicities and we demonstrate that it is not caused by the proposed helium enhancements and/or young ages. Hence, these stars formed from a gas already depleted in lithium. Finally, we note that Omega Centauri includes all the populations (Li-normal/Na-normal, Li-normal/Na-rich, and Li-poor/Na-rich stars) observed, to a lesser extent, in mono-metallic GCs.

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Supermassive black holes: Coevolution (or not) of black holes and host galaxies

Proceedings of the International Astronomical Union ◽

10.1017/s174392131300495x ◽

2012 ◽

Vol 8 (S295) ◽

pp. 241-256

Author(s):

John Kormendy

Keyword(s):

Black Holes ◽

Galaxy Formation ◽

Globular Clusters ◽

Hubble Space Telescope ◽

Supermassive Black Holes ◽

Host Galaxy ◽

Late Time ◽

Host Galaxies ◽

Energy Feedback ◽

Negative Effect

AbstractSupermassive black holes (BHs) have been found in 75 galaxies by observing spatially resolved dynamics. The Hubble Space Telescope (HST) revolutionized BH work by advancing the subject from its ‘proof of concept’ phase into quantitative studies of BH demographics. Most influential was the discovery of a tight correlation between BH masses M• and the velocity dispersions σ of stars in the host galaxy bulge components at radii where the stars mostly feel each other and not the BH. Together with correlations between M• and bulge luminosity, with the ‘missing light’ that defines galaxy cores, and with numbers of globular clusters, this has led to the conclusion that BHs and bulges coevolve by regulating each other's growth. This simple picture with one set of correlations for all galaxies dominated BH work in the past decade.New results are now replacing the above, simple story with a richer and more plausible picture in which BHs correlate differently with different kinds of galaxy components. BHs with masses of 105—106M⊙ live in some bulgeless galaxies. So classical (merger-built) bulges are not necessary equipment for BH formation. On the other hand, while they live in galaxy disks, BHs do not correlate with galaxy disks or with disk-grown pseudobulges. They also have no special correlation with dark matter halos beyond the fact that halo gravity controls galaxy formation. This leads to the suggestion that there are two modes of BH feeding, (1) local, secular and episodic feeding of small BHs in largely bulgeless galaxies that involves too little energy feedback to drive BH–host-galaxy coevolution and (2) global feeding in major galaxy mergers that rapidly grows giant BHs in short-duration events whose energy feedback does affect galaxy formation. After these quasar-like phases, maintenance-mode BH feedback into hot, X-ray-emitting gas continues to have a primarily negative effect in preventing late-time star formation when cold gas or gas-rich galaxies get accreted. Finally, the highest-mass galaxies inherit coevolution effects from smaller galaxies; the tightness of their BH correlations is caused mainly by averaging during dissipationless major mergers.

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Exploring the nature and synchronicity of early cluster formation in the Large Magellanic Cloud – IV. Evidence for multiple populations in Hodge 11 and NGC 2210

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1174 ◽

2019 ◽

Vol 486 (4) ◽

pp. 5581-5599 ◽

Cited By ~ 5

Author(s):

Christina K Gilligan ◽

Brian Chaboyer ◽

Jeffrey D Cummings ◽

Dougal Mackey ◽

Roger E Cohen ◽

...

Keyword(s):

Globular Clusters ◽

Main Sequence ◽

Hubble Space Telescope ◽

Cluster Formation ◽

Stellar Populations ◽

Large Magellanic Cloud ◽

Magellanic Cloud ◽

Wide Field ◽

Horizontal Branch ◽

Advanced Camera For Surveys

Abstract We present a multiple population search in two old Large Magellanic Cloud (LMC) Globular clusters, Hodge 11 and NGC 2210. This work uses data from the Advanced Camera for Surveys and Wide Field Camera 3 on the Hubble Space Telescope from programme GO-14164 in Cycle 23. Both of these clusters exhibit a broadened main sequence with the second population representing (20 ± ∼5) per cent for NGC 2210 and (30 ± ∼5) per cent for Hodge 11. In both clusters, the smaller population is redder than the primary population, suggesting CNO variations. Hodge 11 also displays a bluer second population in the horizontal branch, which is evidence for helium enhancement. However, even though NGC 2210 shows similarities to Hodge 11 in the main sequence, there does not appear to be a second population on NGC 2210’s horizontal branch. This is the first photometric evidence that ancient LMC Globular clusters exhibit multiple stellar populations.

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