Forecasting the Population of Globular Cluster Streams in Milky Way-type Galaxies (2405.15851v2)

Abstract: Thin stellar streams originating from globular clusters are among the most sensitive tracers of low-mass dark-matter subhalos. Joint analysis of the entire population of stellar streams will place the most robust constraints on the dark-matter subhalo mass function, and therefore the nature of dark matter. Here we use a hierarchical model of globular cluster formation to forecast the total number, masses and radial distribution of dissolved globular cluster in Milky Way-like galaxies. Furthermore, we generate mock stellar streams from these progenitors' orbital histories taking into account the clusters' formation and accretion time, mass, and metallicity. Out of $\sim$10,000 clusters more massive than $10^4$ M$_{\odot}$, $\sim$9000 dissolved in the central bulge and are fully phase-mixed at the present, while the remaining $\sim$1000 survive as coherent stellar streams. This suggests that the current census of $\sim$80 globular cluster streams in the Milky Way is severely incomplete. Beyond 15 kpc from the Galactic center we are missing hundreds of streams, of which the vast majority are from accreted GCs. Deep Rubin photometry $(g\lesssim27.5)$ would be able to detect these streams, even the most distant ones beyond $> 75$ kpc. We also find that M31 will have an abundance of streams at galactocentric radii of 30-100 kpc. We conclude that future surveys will find a multitude of stellar streams from globular clusters which can be used for dark matter subhalo searches.

• The paper integrates hierarchical globular cluster formation with orbital simulations to forecast stream properties in Milky Way-type galaxies.
• It finds that about 1,000 coherent stellar streams remain from ~10,000 clusters, with numerous streams undetected at galactocentric radii beyond 15 kpc.
• The study emphasizes deep photometry, such as with the Vera C. Rubin Observatory, to uncover missing streams and refine dark matter constraints.

Forecasting the Population of Globular Cluster Streams in Milky Way-type Galaxies

The paper "Forecasting the Population of Globular Cluster Streams in Milky Way-type Galaxies" by Pearson et al. offers a detailed paper and simulation-based analysis on the properties, distribution, and observability of globular cluster (GC) streams in Milky Way-like galaxies. The authors employ hierarchical models of globular cluster formation to predict the characteristics and numbers of thin stellar streams resulting from globular cluster dissolution. The paper provides a substantial contribution to our understanding of the GC stream population and its implications for larger astrophysical questions, including dark matter research.

Model and Results

The authors utilize a combination of a hierarchical model for GC formation with mock stellar stream generation based on orbital integration in Milky Way-type gravitational potentials. The simulations include initial conditions and parameters derived from the TNG50 cosmological simulations and are adjusted to match the Milky Way's halo properties.

Key numerical findings from the simulation indicate that:

• Out of approximately 10,000 clusters with initial masses greater than $10^4 M_{\odot}$, around 9,000 have dissolved into the central bulge and are currently fully phase-mixed, whereas approximately 1,000 survive as coherent stellar streams.
• At galactocentric radii beyond 15 kpc, there is a significant deficit of observable streams, suggesting that approximately 100 streams remain undetected, primarily from accreted globular clusters.
• The paper predicts that deep photometry, achievable with the Vera C. Rubin Observatory, could reveal these missing streams even at distances greater than 75 kpc from the Galactic center.

Implications and Future Prospects

The research suggests that our current observational sample of GC streams within the Milky Way is severely incomplete. A more complete census that includes the fainter and more distant streams could have profound implications for our understanding of the diffuse halo structure and the potential perturbations from dark matter subhalos.

The authors emphasize the potential for future surveys to capitalize on these findings. The discovery and analysis of additional streams could refine models of halo dynamics and subhalo distribution, directly impacting the constraints we can place on dark matter models through mechanisms like stream gap and perturbation analyses.

Analytical Adjustments and Considerations

The paper also highlights several methodological considerations:

• The characterization of the gravitational potential relies extensively on approximations from static, three-component models fit to the observed properties of host galaxies in the Illustris TNG50 simulations.
• Dynamical friction, stream self-gravity, and the potential impact of baryonic structures like the Galactic bar and spiral arms are acknowledged as factors that might further influence stream morphology and detectability.

Broader Astrophysical Context

The detection and paper of GC streams in the outskirts of the Milky Way and in extragalactic settings, such as in M31, enrich our astrophysical toolkit for probing the halo and unveiling the low-mass structure in the universe. Furthermore, GC streams provide natural tracers of past dynamical events, accretion history, and the overall assembly of galaxies.

In summary, Pearson et al.'s paper signposts a frontier of discovery within Galactic astronomy. By forecasting the properties and distribution of GC streams, it not only invites a re-evaluation of the observational strategies currently employed but also emphasizes the potential scientific returns from upcoming all-sky surveys and deep photometric projects. These findings pave the way for nuanced inquiry into the intersection of galactic dynamics, dark matter, and the evolving cosmic landscape.