Fossil stellar streams and their globular cluster populations in the E-MOSAICS simulations

Monthly Notices of the Royal Astronomical Society

et al. 2020

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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 × 10 3 and 10 5 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 sub-dominant 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.

Section: Summary Of the E-mosaics Simulationsmentioning

confidence: 99%

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

Reina-Campos

Hughes

Monthly Notices of the Royal Astronomical Society

et al. 2020

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“…We evaluate the role of reionization in (metal-poor) GC formation using the E-MOSAICS simulations, which have the advantage of populating galaxies with GCs in a self-consistent fashion and also including a model for their disruption, both of which are crucial for reproducing the observed GC population in the local Universe (see Sect. 3, Pfeffer et al 2018;Usher et al 2018;Hughes et al 2019;Kruijssen et al 2019b, Pfeffer et al in prep). During the epoch of reionization suggested by observations (6 z 10, Robertson et al 2015), merely ∼10 per cent of the metal-poor GC mass has formed across the 25 present-day Milky Way-mass galaxies present in our sample.…”

Section: Formation Histories Of Metallicity Subsamples Of Stars Clusmentioning

confidence: 99%

Formation histories of stars, clusters, and globular clusters in the E-MOSAICS simulations

Reina-Campos

Monthly Notices of the Royal Astronomical Society

Pfeffer

et al. 2019

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The formation histories of globular clusters (GCs) are a key diagnostic for understanding their relation to the evolution of the Universe through cosmic time. We use the suite of 25 cosmological zoom-in simulations of present-day Milky Way-mass galaxies from the E-MOSAICS project to study the formation histories of stars, clusters, and GCs, and how these are affected by the environmental dependence of the cluster formation physics. We find that the median lookback time of GC formation in these galaxies is ∼10.73 Gyr (z = 2.1), roughly 2.5 Gyr earlier than that of the field stars (∼8.34 Gyr or z = 1.1). The epoch of peak GC formation is mainly determined by the time evolution of the maximum cluster mass, which depends on the galactic environment and largely increases with the gas pressure. Different metallicity subpopulations of stars, clusters and GCs present overlapping formation histories, implying that star and cluster formation represent continuous processes. The metal-poor GCs (−2.5 < [Fe/H] < −1.5) of our galaxies are older than the metal-rich GC subpopulation (−1.0 < [Fe/H] < −0.5), forming 12.13 Gyr and 10.15 Gyr ago (z = 3.7 and z = 1.8), respectively. The median ages of GCs are found to decrease gradually with increasing metallicity, which suggests different GC metallicity subpopulations do not form independently and their spatial and kinematic distributions are the result of their evolution in the context of hierarchical galaxy formation and evolution. We predict that proto-GC formation is most prevalent at 2 z 3, which could be tested with observations of lensed galaxies using JWST.

“…In several published (Paper I; Kruijssen et al 2019;Usher et al 2018;Reina-Campos et al 2018;Hughes et al 2019), submitted (e.g. Reina-Campos et al 2019;Pfeffer et al 2019), and upcoming papers, we are carrying out a detailed comparison of the modelled GC populations at z = 0 to observed GC populations in the local Universe.…”

Section: Validation By Comparison To the Galactic Gc Populationmentioning

confidence: 99%

The E-MOSAICS project: tracing galaxy formation and assembly with the age–metallicity distribution of globular clusters

Monthly Notices of the Royal Astronomical Society

Pfeffer

Crain

et al. 2019

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153

277

We present 25 cosmological zoom-in simulations of Milky Way-mass galaxies in the 'MOdelling Star cluster population Assembly In Cosmological Simulations within EAGLE' (E-MOSAICS) project. E-MOSAICS couples a detailed physical model for the formation, evolution, and disruption of star clusters to the EAGLE galaxy formation simulations. This enables following the co-formation and co-evolution of galaxies and their star cluster populations, thus realising the long-standing promise of using globular clusters (GCs) as tracers of galaxy formation and assembly. The simulations show that the age-metallicity distributions of GC populations exhibit strong galaxy-to-galaxy variations, resulting from differences in their evolutionary histories. We develop a formalism for systematically constraining the assembly histories of galaxies using GC age-metallicity distributions. These distributions are characterised through 13 metrics that we correlate with 30 quantities describing galaxy formation and assembly (e.g. halo properties, formation/assembly redshifts, stellar mass assembly timescales, galaxy merger statistics), resulting in 20 statistically (highly) significant correlations. The GC age-metallicity distribution is a sensitive probe of the mass growth, metal enrichment, and minor merger history of the host galaxy. No such relation is found between GCs and major mergers, which play a sub-dominant role in GC formation for Milky Way-mass galaxies. Finally, we show how the GC age-metallicity distribution enables the reconstruction of the host galaxy's merger tree, allowing us to identify all progenitors with masses M * 10 8 M for redshifts 1 z 2.5. These results demonstrate that cosmological simulations of the coformation and co-evolution of GCs and their host galaxies successfully unlock the potential of GCs as quantitative tracers of galaxy formation and assembly.