Since I ended my Marie Curie Fellowship after 5.5 months, I only filled the first gap and completed the first scientific objective, which was to predict where thin streams from globular clusters reside in external galaxies using theoretical models and simulations.
Thin star streams from gravitationally bound groups of ~50,000 stars (globular clusters) are excellent tools for detecting small dark matter clumps. Analyzing all star streams together will help us understand the distribution of dark matter and its properties. To investigate how many and where thin streams from globular clusters exist, we used a model to predict the number, size, and locations of dissolved globular clusters in galaxies like the Milky Way. The model builds upon previous studies which simulate the formation and evolution of individual globular clusters. This model helps us create detailed mock catalogs of GCs with properties like mass, age, metallicity, positions, and velocities that match real GCs. We then use these catalogs to model star streams in our study. The catalogs are based on an analytical model of globular cluster formation and evolution in selected galaxies from large scale simulations of our Universe. This model includes a detailed process of how tidal forces break up clusters, which shapes their initial masses to match current observations. The model works in four steps:
1) Formation of globular clusters: globular clusters form when their parent galaxy undergoes a major merger or rapid growth.
2) Cluster sampling: We use observed relationships to calculate the gas mass and metallicity of the parent galaxy.
3) Particle assignment: The total mass of the new clusters is assumed to be proportional to the cold gas mass, and their metallicity is inherited from the parent galaxy.
4) Tidal disruption: The model estimates the time it takes for clusters to break apart, which is crucial for accurately modeling the star streams that come from these clusters.
In essence, this model helps us understand how globular clusters form, evolve, and eventually break apart, providing a reliable basis for studying star streams.
We also created simulated star streams from these clusters based on their history, formation time, mass, and metal content.
We found that a Milky Way type galaxy, should have around 10,000 fully dissolved clusters, of which about 9,000 dissolved in the central bulge and are now fully mixed, while the remaining 1,000 still exist as distinct stellar streams in the Galaxy. This means our current count of about 80 globular cluster streams in the Milky Way is far too low. Beyond 15,000 light-years from the center of the galaxy, we're missing hundreds of streams, mostly from clusters that merged with our galaxy. Deep photometry from the Rubin Observatory could detect these streams, even the distant ones beyond 75,000 light-years. We also expect the Andromeda galaxy to have many streams between 30,000 and 100,000 light-years from its center. Future surveys will likely find many more star streams from globular clusters, which can help in searching for dark matter clumps, as these clumps leave signatures of gaps in streams if the clumps pass near a stellar stream.
