Catalog of Mock Stellar Streams in Milky Way-Like Galaxies

TL;DR

This work addresses the challenge of modeling globular-cluster streams in Milky Way–like galaxies to support dynamical inferences of the Galactic potential and dark-matter substructure. It builds a comprehensive mock catalog by combining a cosmologically informed GC-evolution model, time-dependent potentials from basis-function expansions fitted to Illustris-TNG50-1 and FIRE-2 simulations, and an efficient particle-spray method for real-time stream realization. The authors find that stream lengths, widths, and proper motions follow power-law trends with galactocentric radius beyond 10 kpc and provide mock photometry for Gaia, LSST, and Roman, predicting a substantial increase in detectable streams with the next-generation surveys. The catalog, comprising 1473 streams across four MW-like halos, is publicly available and suitable for population statistics, potential modeling, and calibrating stream-based Galactic investigations.

Abstract

Dynamically cold stellar streams from tidally dissolved globular clusters (GCs) serve as excellent tools to measure the Galactic mass distribution and show promise to probe the nature of dark matter. For successful application of these tools to observations, it is essential to have an accurate model of stellar stream properties on the Galactic scale. To this end we produce a mock catalog of stellar streams in four simulated Milky Way-like galaxies. We build the catalog with three main components: a model for the formation and disruption of globular clusters based on cosmological simulations, time-dependent potentials constructed with basis function expansions for integrating stream orbits, and an improved particle spray algorithm for efficient generation of stellar streams. We find that the observable widths and lengths of mock streams as a function of galactocentric radius are well described by power-laws for streams beyond 10 kpc. We generate mock photometry for Gaia, LSST, and Roman, and find that the latter two surveys will increase the number of observable stars in GC stellar streams by several orders of magnitude. Our full catalog, containing stream populations across four different galaxy realizations, is publicly available and can be used to study stream population statistics and to calibrate models which use stellar streams to understand our Galaxy.

Figures (13)

• Figure 1: Evolution of the mass function over time for a $2\times10^{4}\,{\mathrm{M}_\odot}$ cluster on a Pal 5-like orbit with stellar ejection probability $p \propto m^{-1/2}$ and assumed metallicity of $\mathrm{[Fe/H]} = -1.56$ (the observed metallicity of Pal 5). The cluster becomes less dominated by low-mass stars gradually over time because they are more likely to be ejected than high-mass stars.
• Figure 2: All sky map of the final collection of disrupted features for the TNG halo 523889 with $g < 24.5$. Color indicates the metallicity of the original star cluster. Positions and apparent magnitudes of stars are calculated with the standard astropy convention where the Sun is placed at $(-8 \rm ~kpc, 0 ~kpc, 20.8 ~pc)$ in our galactocentric reference frame.
• Figure 3: Four example streams with stars color-coded by their ejection lookback time. Each stream's present day galactocentric radius is shown down and to the left of its progenitor location, as indicated by region where the ejection time approaches 0 Gyr.
• Figure 4: Examples of streams from the catalog at a range of present day galactocentric radii with a photometric cut $g < 24.5$. The top stream subtends the longest extent on the sky at nearly $250^{\circ}$ and its close proximity to the Galactic center has heated it and caused the stream to extend in $\phi_2$. The middle stream progenitor fully disrupted approximately $470 \rm ~Myr$ ago, causing a gap along the stream profile. The final stream at $47$ kpc from the Galactic center is dynamically the coldest, making it the shortest and thinnest of the three shown.
• Figure 5: Variation of each stream in $(\phi_1, \phi_2)$ coordinates as a function of the galactocentric radius of the progenitor orbit for stars with $g < 24.5$. The top row shows the dispersion for each stream in both $\phi_1$ and $\phi_2$, where as the bottom row shows the dispersion in the proper motions of each coordinate. Filled circles show thin streams, while open circles show wide streams. Streams closer to the Galactic center are dynamically hotter than streams further away and therefore exhibit a larger variation. Lines show best-fit power law relations at $r > 10$ kpc for the three magnitude cuts: LSST (solid line), Roman (dot line), and Gaia (dot-dashed line).