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

Usher, Christopher; Brodie, Jean P.; Forbes, Duncan A.; Romanowsky, Aaron J.; Strader, Jay; Pfeffer, Joel; Bastian, Nate

doi:10.1093/mnras/stz2596

Cited by 51 publications

(58 citation statements)

References 230 publications

(381 reference statements)

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“…The analysis showed that the Milky Way experienced a total of ∼ 15 mergers throughout its history, with the last major merger having taken place at z > 4, thus sharpening previous limits of z > 2 (e.g., Wyse 2001;Hammer et al 2007;Stewart et al 2008). Improved determinations of the ages of extragalactic GCs may enable the application of these correlations to galaxies beyond the Milky Way in the near future (Usher et al 2019). In addition, the analysis presented by predicted the existence of the satellite Gaia-Enceladus/Sausage (GES), which was discovered only weeks later in the data from Gaia's second data release (e.g., Myeong et al 2018;Helmi et al 2018), as well as the enigmatic galaxy Kraken, which together with the GES accretion event forms the two most massive galaxies ever accreted by the Milky Way.…”

Section: Cluster Populations As Tracers Of Galaxy Assemblymentioning

confidence: 92%

Star Clusters Near and Far

et al. 2020

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Star clusters are fundamental units of stellar feedback and unique tracers of their host galactic properties. In this review, we will first focus on their constituents, i.e. detailed insight into their stellar populations and their surrounding ionised, warm, neutral, and molecular gas. We, then, move beyond the Local Group to review star cluster populations at various evolutionary stages, and in diverse galactic environmental conditions accessible in the local Universe. At high redshift, where conditions for cluster formation and evolution are more extreme, we are only able to observe the integrated light of a handful of objects that we believe will become globular clusters. We therefore discuss how numerical and analytical methods, informed by the observed properties of cluster populations in the local Universe, are used to develop sophisticated simulations potentially capable of disentangling the genetic map of galaxy formation and assembly that is carried by globular cluster populations.

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Section: Cluster Populations As Tracers Of Galaxy Assemblymentioning

confidence: 92%

Star Clusters Near and Far

et al. 2020

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“…This limits the sample of galaxies with accurate GC population ages to a the Local Group, which may bias our observational picture of when the 'typical' GC forms. Observations of nearby early-type galaxies suggest that they may contain a younger GC population compared to the MW (Usher et al 2019).…”

Section: Comparison To Observationsmentioning

confidence: 99%

Where did the globular clusters of the Milky Way form? Insights from the E-MOSAICS simulations

Keller

Kruijssen

Pfeffer

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Globular clusters (GCs) are typically old, with most having formed at z ≳ 2. This makes understanding their birth environments difficult, as they are typically too distant to observe with sufficient angular resolution to resolve GC birth sites. Using 25 cosmological zoom-in simulations of Milky Way-like galaxies from the E-MOSAICS project, with physically motivated models for star formation, feedback, and the formation, evolution, and disruption of GCs, we identify the birth environments of present-day GCs. We find roughly half of GCs in these galaxies formed in situ (52.0 ± 1.0 per cent) between z ≈ 2–4, in turbulent, high-pressure discs fed by gas that was accreted without ever being strongly heated through a virial shock or feedback. A minority of GCs form during mergers (12.6 ± 0.6 per cent in major mergers, and 7.2 ± 0.5 per cent in minor mergers), but we find that mergers are important for preserving the GCs seen today by ejecting them from their natal, high density interstellar medium (ISM), where proto-GCs are rapidly destroyed due to tidal shocks from ISM substructure. This chaotic history of hierarchical galaxy assembly acts to mix the spatial and kinematic distribution of GCs formed through different channels, making it difficult to use observable GC properties to distinguish GCs formed in mergers from ones formed by smooth accretion, and similarly GCs formed in situ from those formed ex situ. These results suggest a simple picture of GC formation, in which GCs are a natural outcome of normal star formation in the typical, gas-rich galaxies that are the progenitors of present-day galaxies.

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“…Otherwise, the GC ages have typical random uncertainties of > 2 Gyr, reflecting the challenging age determination of old stellar populations (e.g. Usher et al 2019, or App. in Fahrion et al 2019b.…”

Section: Globular Cluster Agesmentioning

confidence: 99%

The Fornax 3D project: Non-linear colour–metallicity relation of globular clusters

Fahrion

Lyubenova

Hilker

et al. 2020

A&A

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Globular cluster (GC) systems of massive galaxies often show a bimodal colour distribution. This has been interpreted as a metallicity bimodality, created by a two-stage galaxy formation where the red, metal-rich GCs were formed in the parent halo and the blue metal-poor GCs were accreted. This interpretation, however, crucially depends on the assumption that GCs are exclusively old stellar systems with a linear colour-metallicity relation (CZR). The shape of the CZR and range of GC ages are currently under debate, because their study requires high quality spectra to derive reliable stellar population properties. We determined metallicities with full spectral fitting from a sample of 187 GCs with high spectral signal-to-noise ratio in 23 galaxies of the Fornax cluster that were observed as part of the Fornax 3D project. The derived CZR from this sample is non-linear and can be described by a piecewise linear function with a break point at (g − z) ∼ 1.1 mag. The less massive galaxies in our sample (M * < 10 10 M ) appear to have slightly younger GCs, but the shape of the CZR is insensitive to the GC ages. Although the least massive galaxies lack red, metal-rich GCs, a non-linear CZR is found irrespective of the galaxy mass, even in the most massive galaxies (M * ≥ 10 11 M ). Our CZR predicts narrow unimodal GC metallicity distributions for low mass and broad unimodal distributions for very massive galaxies, dominated by a metal-poor and metal-rich peak, respectively, and bimodal distributions for galaxies with intermediate masses (10 10 ≤ M * < 10 11 M ) as a consequence of the relative fraction of red and blue GCs. The diverse metallicity distributions challenge the simple differentiation of GC populations solely based on their colour.

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

Cited by 51 publications

References 230 publications

Star Clusters Near and Far

Star Clusters Near and Far

Where did the globular clusters of the Milky Way form? Insights from the E-MOSAICS simulations

The Fornax 3D project: Non-linear colour–metallicity relation of globular clusters

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