Broken and unbroken: the Milky Way and M31 stellar haloes

Abstract

We use the Bullock & Johnston suite of simulations to study the density profiles of L*-type galaxy stellar haloes. Observations of the Milky Way and M31 stellar haloes show contrasting results: the Milky Way has a `broken' profile, where the density falls off more rapidly beyond ~ 25 kpc, while M31 has a smooth profile out to 100 kpc with no obvious break. Simulated stellar haloes, built solely by the accretion of dwarf galaxies, also exhibit this behavior: some haloes have breaks, while others don't. The presence or absence of a break in the stellar halo profile can be related to the accretion history of the galaxy. We find that a break radius is strongly related to the build up of stars at apocentres. We relate these findings to observations, and find that the `break' in the Milky Way density profile is likely associated with a relatively early (~ 6-9 Gyr ago) and massive accretion event. In contrast, the absence of a break in the M31 stellar halo profile suggests that its accreted satellites have a wide range of apocentres. Hence, it is likely that M31 has had a much more prolonged accretion history than the Milky Way.

9 pages, 7 figures. Accepted for publication by ApJ

References in corpus (8)

• The accretion origin of the Milky Way's stellar halo
• The Haunted Halos of Andromeda and Triangulum: A panorama of galaxy formation in action
• Tracing Galaxy Formation with Stellar Halos II: Relating Substructure in Phase- and Abundance-Space to Accretion Histories
• The Dual Origin of Stellar Halos
• The Metal-Poor Halo of the Andromeda Spiral Galaxy (M31)
• The Hercules-Aquila Cloud
• Global Properties of M31's Stellar Halo from the SPLASH Survey. I. Surface Brightness Profile
• Stellar Kinematics in the Complicated Inner Spheroid of M31: Discovery of Substructure Along the Southeastern Minor Axis and its Relationship to the Giant Southern Stream

Cited by in corpus (146)

• The Galaxy in Context: Structural, Kinematic and Integrated Properties
• Exploring the Milky Way stellar disk. A detailed elemental abundance study of 714 F and G dwarf stars in the Solar neighbourhood
• Co-formation of the Galactic disc and the stellar halo
• The stellar mass assembly of galaxies in the Illustris simulation: growth by mergers and the spatial distribution of accreted stars
• Streams, substructures and the early history of the Milky Way
• 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
• The Biggest Splash
• The origin of accreted stellar halo populations in the Milky Way using APOGEE, $\text{Gaia}$, and the EAGLE simulations
• The large-scale structure of the halo of the Andromeda Galaxy Part I: global stellar density, morphology and metallicity properties
• Kraken reveals itself -- the merger history of the Milky Way reconstructed with the E-MOSAICS simulations
• The extended halo of Centaurus A: uncovering satellites, streams, and substructures
• The Sausage Globular Clusters
• From dawn till disk: Milky Way's turbulent youth revealed by the APOGEE+Gaia data
• Gaia reveals a metal-rich in-situ component of the local stellar halo
• The Fornax Deep Survey with VST. I. The extended and diffuse stellar halo of NGC~1399 out to 192 kpc
• The Auriga Stellar Haloes: Connecting stellar population properties with accretion and merging history
• Contributions to the accreted stellar halo: an atlas of stellar deposition
• Halo Mass and Assembly History Exposed in the Faint Outskirts: the Stellar and Dark Matter Haloes of Illustris Galaxies
• Evidence for an Intermediate-Mass Milky Way from Gaia DR2 Halo Globular Cluster Motions
• Mapping the Stellar Halo with the H3 Spectroscopic Survey
• Overview of the DESI Milky Way Survey
• Ages and kinematics of chemically selected, accreted Milky Way halo stars
• Dynamical Relics of the Ancient Galactic Halo
• The total stellar halo mass of the Milky Way
• The E-MOSAICS project: tracing galaxy formation and assembly with the age-metallicity distribution of globular clusters
• The shape of the Galactic halo with $Gaia$ DR2 RR Lyrae. Anatomy of an ancient major merger
• Apocenter Pile-Up: Origin of the Stellar Halo Density Break
• The origin of galactic metal-rich stellar halo components with highly eccentric orbits
• The Dragonfly Nearby Galaxies Survey. I. Substantial variation in the diffuse stellar halos around spiral galaxies
• Diverse Stellar Haloes in Nearby Milky Way-Mass Disc Galaxies
• The mass of our Milky Way
• The origin of the Milky Way globular clusters
• Estimating the dark matter halo mass of our Milky Way using dynamical tracers
• Clouds, Streams and Bridges. Redrawing the blueprint of the Magellanic System with Gaia DR1
• The GHOSTS survey. II. The diversity of Halo Color and Metallicity Profiles of Massive Disk Galaxies
• Discovery of $\sim$ 9,000 new RR Lyrae in the Southern Catalina Surveys
• Inferred Evidence For Dark Matter Kinematic Substructure with SDSS-Gaia
• Weighing the stellar constituents of the Galactic halo with APOGEE red giant stars
• The Eating Habits of Milky Way Mass Halos: Destroyed Dwarf Satellites and the Metallicity Distribution of Accreted Stars
• Chemo-kinematics of the $Gaia$ RR Lyrae: the halo and the disc
• Galactic Archaeology. The dwarfs that survived and perished
• Selecting accreted populations: metallicity, elemental abundances, and ages of the Gaia-Sausage-Enceladus and Sequoia populations
• The ISLAndS project II: The Lifetime Star Formation Histories of Six Andromeda dSphs
• The ARTEMIS simulations: stellar haloes of Milky Way-mass galaxies
• The Halo's Ancient Metal-Rich Progenitor Revealed with BHB Stars
• Touching The Void: A Striking Drop in Stellar Halo Density Beyond 50 kpc
• VEGAS: A VST Early-type GAlaxy Survey. II. Photometric study of giant ellipticals and their stellar halos
• The first all-sky view of the Milky Way stellar halo with Gaia+2MASS RR Lyrae
• Bulge Formation via Mergers in Cosmological Simulations
• Galactic Archaeology with Gaia
• GASTRO library I: the simulated chemodynamical properties of several GSE-like stellar halos
• The Fornax Deep Survey with VST. VIII. Connecting the accretion history with the cluster density
• Balancing mass and momentum in the Local Group
• Nitrogen enrichment and clustered star formation at the dawn of the Galaxy
• The Gaia-ESO Survey: a quiescent Milky Way with no significant dark/stellar accreted disc
• Common origin for Hercules-Aquila and Virgo Clouds in Gaia DR2
• The Progenitors of the Milky Way Stellar Halo: Big Bricks Favoured over Little Bricks
• Anisotropy of the Milky Way's stellar halo using K giants from LAMOST and $Gaia$
• The Edge of the Galaxy
• Star Clusters in Evolving Galaxies
• Merger-induced galaxy transformations in the ARTEMIS simulations
• EMERGE: Empirical predictions of galaxy merger rates since $z\sim 6$
• The Velocity Anisotropy of Distant Milky Way Halo Stars from Hubble Space Telescope Proper Motions
• Quantifying the Stellar Halo's Response to the LMC's Infall with Spherical Harmonics
• Stellar Halos in Illustris- Probing the Histories of Milky Way-Mass Galaxies
• Vast planes of satellites in a high resolution simulation of the Local Group: comparison to Andromeda
• A missing outskirts problem? Comparisons between stellar halos in the Dragonfly Nearby Galaxies Survey and the TNG100 simulation
• Can cosmological simulations capture the diverse satellite populations of observed Milky Way analogues?
• Constraints on the assembly history of the Milky Way's smooth, diffuse stellar halo from the metallicity-dependent, radially-dominated velocity anisotropy profiles probed with K giants and BHB stars using LAMOST, SDSS/SEGUE, and Gaia
• Discovery of distant RR Lyrae stars in the Milky Way using DECam
• Cosmic phylogeny: reconstructing the chemical history of the solar neighbourhood with an evolutionary tree
• The little things matter: relating the abundance of ultrafaint satellites to the hosts' assembly history
• Unmixing the Galactic Halo with RR Lyrae tagging
• A "Light," Centrally-Concentrated Milky Way Halo?
• Creating mock catalogues of stellar haloes from cosmological simulations
• Energy wrinkles and phase-space folds of the last major merger
• Dynamics of astrophysical objects against the cosmological background
• The Fornax Cluster VLT Spectroscopic Survey II - Planetary Nebulae kinematics within 200 kpc of the cluster core
• The Milky Way's Shell Structure Reveals the Time of a Radial Collision
• Metallicity Bias in the Kinematics of the Milky Way Stellar Halo
• The aftermath of the Great Collision between our Galaxy and the Large Magellanic Cloud
• Mapping the Milky Way with LAMOST II: the stellar halo
• The Survey of Centaurus A's Baryonic Structures (SCABS). II. The Extended Globular Cluster System of NGC5128 and its Nearby Environment
• Estimating the Galactic Mass Profile in the Presence of Incomplete Data
• The hunt for the Milky Way's accreted disc
• VEGAS: VST Early-type GAlaxy Survey. V. IC 1459 group: Mass assembly history in low density environments
• Substructure and Tidal Streams in the Andromeda Galaxy and its Satellites
• Evidence for sub-Chandrasekhar Type Ia supernovae from the last major merger
• The Local Stellar Halo is Not Dominated by a Single Radial Merger Event
• HALO7D II: The Halo Velocity Ellipsoid and Velocity Anisotropy with Distant Main Sequence Stars
• Identifying RR Lyrae Variable Stars in Six Years of the Dark Energy Survey
• Probing the Galactic Halo with RR Lyrae Stars. II. The Substructures of the Milky Way
• Distant Echoes of the Milky Way's Last Major Merger
• Beta Dips in the Gaia Era: Simulation Predictions of the Galactic Velocity Anisotropy Parameter for Stellar Halos
• The accreted stellar halo as a window on halo assembly in L* galaxies
• Mapping the anisotropic Galactic stellar halo with Blue Horizontal Branch stars
• The Hough Stream Spotter: A New Method for Detecting Linear Structure in Resolved Stars and Application to the Stellar Halo of M31
• The chemodynamics of prograde and retrograde Milky Way stars
• To the Galactic Virial Radius with Hyper Suprime-Cam
• Isotropic at the Break? 3D Kinematics of Milky Way Halo Stars in the Foreground of M31
• A Swing of the Pendulum: The Chemodynamics of the Local Stellar Halo Indicate Contributions from Several Radial Merger Events
• The stellar halo in Local Group Hestia simulations I. The in-situ component and the effect of mergers
• The observable properties of galaxy accretion events in Milky Way-like galaxies in the FIRE-2 cosmological simulations
• Hunting The Most Distant Stars in the Milky Way: Methods and Initial Results
• Quantifying the Smoothness of the Stellar Halo: A Link to Accretion History
• [$\alpha$/Fe] Abundances of Four Outer M 31 Halo Stars
• Probing the Galactic halo with RR Lyrae stars $-$ III. The chemical and kinematic properties of the stellar halo
• The impact of two massive early accretion events in a Milky Way-like galaxy: repercussions for the buildup of the stellar disc and halo
• Exploring the diversity and similarity of radially anisotropic Milky Way-like stellar haloes: implications for disrupted dwarf galaxy searches
• Modelling the Milky Way. I -- Method and first results fitting the thick disk and halo with DES-Y3 data
• HALO7D I: The Line of Sight Velocities of Distant Main Sequence Stars in the Milky Way Halo
• Elemental Abundances in M31: Properties of the Inner Stellar Halo
• Linking nearby stellar streams to more distant halo overdensities
• Hyper Wide Field Imaging of the Local Group Dwarf Irregular Galaxy IC 1613: An Extended Component of Metal-poor Stars
• The effect of secular galactic growth on the evolution of star clusters
• On the assembly history of massive galaxies. A pilot project with VEGAS deep imaging and M3G integral field spectroscopy
• Evidence For Multiple Accretion Events in the $Gaia$-Sausage/Enceladus Structures
• On the Edge: the relation between stellar and dark matter haloes of Milky Way-mass galaxies
• The Early Merger that Made the Galaxy's Stellar Halo
• Ironing the folds: The phase space chevrons of a GSE-like merger as a dark matter subhalo detector
• Influence of the Gaia-Sausage-Enceladus on the density shape of the Galactic stellar halo revealed by halo K giants from the LAMOST survey
• Tracing the Metal-Poor M31 Stellar Halo with Blue Horizontal Branch Stars
• Chemodynamical study of two CEMP-no stars from the Hamburg/ESO Survey
• Observing the stellar halo of Andromeda in cosmological simulations: the Auriga2PAndAS pipeline
• The Density Profile and Kinematics of the Milky Way with RR Lyrae Stars
• An Accurate Comprehensive Approach to Substructure: III. Masses and Formation Times of the Host Haloes
• Isothermal distributions in MONDian gravity as a simple unifying explanation for the ubiquitous $\rho \propto r^{-3}$ density profiles in tenuous stellar halos
• The role of accreted and in situ populations in shaping the stellar halos of low-mass galaxies
• Accelerated phase-mixing in the stellar halo due to a rotating bar
• Existence of the Metal-Rich Stellar Halo and High-velocity Thick Disk in the Galaxy
• Fading Features Found in the Kinematics of the Far-Reaching Milky Way Stellar Halo
• Resolved Stellar Populations as Tracers of Outskirts
• Where Did the Outskirts Go? Outer Stellar Haloes as a Sensitive Probe of Supernova Feedback
• The formation and disruption of globular cluster populations in simulations of present-day $L^{\ast }$ galaxies with controlled assembly histories
• AuriDESI: Mock Catalogues for the DESI Milky Way Survey
• A new visit to the variable stars in M56 and its colour magnitude diagram structure
• Mapping Milky Way Halo Substructure using Stars in the Extended Blue Tail of the Horizontal Branch
• Simulations of the accreted stellar halos of low-mass field galaxies
• Architecture of the Andromeda: a quantitative analysis of clustering in the inner stellar halo
• Exploring the connection between stellar halo profiles and accretion histories in $L_{\ast }$ galaxies
• Disentanglement of the chemodynamical assembly: mapping the Milky Way disks
• Stellar halo striations from assumptions of axisymmetry
• Stirring Things Up: Bar-induced substructures in the stellar halo of a cosmological Milky Way analogue
• Stellar halos of bright central galaxies II: Scaling relations, colors and metallicity evolution with redshift
• Characterisation of the Galactic thick disk