Possibilities and Limitations of Kinematically Identifying Stars from Accreted Ultra-Faint Dwarf Galaxies

Abstract

The Milky Way has accreted many ultra-faint dwarf galaxies (UFDs), and stars from these galaxies can be found throughout our Galaxy today. Studying these stars provides insight into galaxy formation and early chemical enrichment, but identifying them is difficult. Clustering stellar dynamics in 4D phase space ($E$, $L_z$, $J_r$, $J_z$) is one method of identifying accreted structure which is currently being utilized in the search for accreted UFDs. We produce 32 simulated stellar halos using particle tagging with the \textit{Caterpillar} simulation suite and thoroughly test the abilities of different clustering algorithms to recover tidally disrupted UFD remnants. We perform over 10,000 clustering runs, testing seven clustering algorithms, roughly twenty hyperparameter choices per algorithm, and six different types of data sets each with up to 32 simulated samples. Of the seven algorithms, HDBSCAN most consistently balances UFD recovery rates and cluster realness rates. We find that even in highly idealized cases, the vast majority of clusters found by clustering algorithms do not correspond to real accreted UFD remnants and we can generally only recover $6\%$ of UFDs remnants at best. These results focus exclusively on groups of stars from UFDs, which have weak dynamic signatures compared to the background of other stars. The recoverable UFD remnants are those that accreted recently, $z_{\text{accretion}}\lesssim 0.5$. Based on these results, we make recommendations to help guide the search for dynamically-linked clusters of UFD stars in observational data. We find that real clusters generally have higher median energy and $J_r$, providing a way to help identify real vs. fake clusters. We also recommend incorporating chemical tagging as a way to improve clustering results.

arXiv comment21 pages, 14 figures, accepted to ApJ

References in corpus (60)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Array Programming with NumPy
• Gaia Data Release 2. Summary of the contents and survey properties
• Planck 2013 results. XVI. Cosmological parameters
• Statistical Properties of X-ray Clusters: Analytic and Numerical Comparisons
• The Rockstar Phase-Space Temporal Halo Finder and the Velocity Offsets of Cluster Cores
• The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
• Tracing Galaxy Formation with Stellar Halos I: Methods
• Co-formation of the Galactic disc and the stellar halo
• Multi-scale initial conditions for cosmological simulations
• The Universal Stellar Mass-Stellar Metallicity Relation for Dwarf Galaxies
• Origin of the Heaviest Elements: the Rapid Neutron-Capture Process
• Gravitationally Consistent Halo Catalogs and Merger Trees for Precision Cosmology
• The Faintest Dwarf Galaxies
• Galactic stellar haloes in the CDM model
• AGAMA: Action-based galaxy modelling architecture
• Eight Ultra-faint Galaxy Candidates Discovered in Year Two of the Dark Energy Survey
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• R-process enrichment from a single event in an ancient dwarf galaxy
• Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure
• The formation and assembly history of the Milky Way revealed by its globular cluster population
• Actions for axisymmetric potentials
• Kraken reveals itself -- the merger history of the Milky Way reconstructed with the E-MOSAICS simulations
• Mapping the substructure in the Galactic halo with the next generation of astrometric satellites
• The Galaxy and its stellar halo: insights on their formation from a hybrid cosmological approach
• Chemical Evolution in Hierarchical Models of Cosmic Structure II: The Formation of the Milky Way Stellar Halo and the Distribution of the Oldest Stars
• The Auriga Stellar Haloes: Connecting stellar population properties with accretion and merging history
• Complete element abundances of nine stars in the r-process galaxy Reticulum II
• From Nuclei to the Cosmos: Tracing Heavy-Element Production with the Oldest Stars
• Reverse engineering the Milky Way
• The $R$-Process Alliance: First Release from the Southern Search for $r$-Process-Enhanced Stars in the Galactic Halo
• Detailed Chemical Abundances in the r-Process-Rich Ultra-Faint Dwarf Galaxy Reticulum 2
• The R-Process Alliance: First Release from the Northern Search for r-Process Enhanced Metal-Poor Stars in the Galactic Halo
• Dynamical Relics of the Ancient Galactic Halo
• Stellar Archaeology -- Exploring the Universe with Metal-Poor Stars
• An R-process enhanced star in the dwarf galaxy Tucana III
• Organized Chaos: Scatter in the relation between stellar mass and halo mass in small galaxies
• Improving the open cluster census. I. Comparison of clustering algorithms applied to Gaia DR2 data
• The Caterpillar Project: A Large Suite of Milky Way Sized Halos
• The $R$-Process Alliance: Fourth Data Release from the Search for $r$-Process-Enhanced Stars in the Galactic Halo
• On the identification of merger debris in the {\it Gaia} Era
• The R-process Alliance: First Magellan/MIKE Release from the Southern Search for R-Process-enhanced Stars
• Kinematics of Highly R-Process-Enhanced Field Stars: Evidence for an Accretion Origin and Detection of Several Groups from Disrupted Satellites
• Enhanced tidal stripping of satellites in the galactic halo from dark matter self-interactions
• The effect of a disc on the population of cuspy and cored dark matter substructures in Milky Way-like galaxies
• Dynamically Tagged Groups of Very Metal-poor Halo Stars from the HK and Hamburg/ESO Surveys
• StarGO: A New Method to Identify the Galactic Origins of Halo Stars
• On the assembly of the Milky Way dwarf satellites and their common mass scale
• The R-Process Alliance: Chemo-Dynamically Tagged Groups of Halo $r$-Process-Enhanced Stars Reveal a Shared Chemical-Evolution History
• The Atari Disk, a Metal-Poor Stellar Population in the Disk System of the Milky Way
• Characterizing the formation history of Milky Way-like stellar haloes with model emulators
• The Origin of r-process Enhanced Metal-Poor Halo Stars In Now-Destroyed Ultra-Faint Dwarf Galaxies
• Chemical Analysis of the Ultra-Faint Dwarf Galaxy Grus~II. Signature of high-mass stellar nucleosynthesis
• Systematic Problems With Using Dark Matter Simulations to Model Stellar Halos
• Comparing semi-analytic particle tagging and hydrodynamical simulations of the Milky Way's stellar halo
• Dissecting galaxy formation models with Sensitivity Analysis -- A new approach to constrain the Milky Way formation history
• On the relevance of chaos for halo stars in the solar neighbourhood II
• Using Action Space Clustering to Constrain the Accretion History of Milky Way like Galaxies
• Particle tagging and its implications for stellar population dynamics
• Statistical properties of substructures around Milky Way-sized haloes and their implications for the formation of stellar streams

Cited by in corpus (9)

• Metallicity Distribution Functions of 13 Ultra-Faint Dwarf Galaxy Candidates from Hubble Space Telescope Narrowband Imaging
• Exploring the diversity and similarity of radially anisotropic Milky Way-like stellar haloes: implications for disrupted dwarf galaxy searches
• On the Reionization-Era Globular Cluster in Low-Mass Galaxy Eridanus II
• Finding $r$-II sibling stars in the Milky Way with the Greedy Optimistic Clustering algorithm
• Robust Clustering of the Local Milky Way Stellar Kinematic Substructures with Gaia eDR3
• Chemical Abundances of the Typhon Stellar Stream
• The oldest stars with low neutron-capture element abundances and origins in ancient dwarf galaxies
• Nearby stellar substructures in the Galactic halo from DESI Milky Way Survey Year 1 Data Release
• Cosmological insights into the early accretion of r-process-enhanced stars II. Dynamical identification of lost members of Reticulum II