The Milky Way stellar halo out to 40 kpc : Squashed, broken but smooth

Abstract

We introduce a new maximum likelihood method to model the density profile of Blue Horizontal Branch and Blue Straggler stars and apply it to the Sloan Digital Sky Survey Data Release 8 (DR8) photometric catalogue. There are a large number (20,000) of these tracers available over an impressive 14,000 square degrees in both Northern and Southern Galactic hemispheres, and they provide a robust measurement of the shape of the Milky Way stellar halo. After masking out stars in the vicinity of the Virgo Overdensity and the Sagittarius stream, the data are consistent with a smooth, oblate stellar halo with a density that follows a broken power-law. The best fitting model has an inner slope = 2.3 and an outer slope = 4.6, together with a break radius occurring at 27 kpc and a constant halo flattening (that is, ratio of minor axis to major axis) of q = 0.6. Although a broken power-law describes the density fall-off most adequately, it is also well fit by an Einasto profile. There is no strong evidence for variations in flattening with radius, or for triaxiality of the stellar halo.

13 pages, 12 figures. Accepted for publication by MNRAS

References in corpus (11)

• The 2.5 m Telescope of the Sloan Digital Sky Survey
• The Eighth Data Release of the Sloan Digital Sky Survey: First Data from SDSS-III
• The Milky Way's Circular Velocity Curve to 60 kpc and an Estimate of the Dark Matter Halo Mass from Kinematics of ~2400 SDSS Blue Horizontal Branch Stars
• Two Stellar Components in the Halo of the Milky Way
• The accretion origin of the Milky Way's stellar halo
• The Galaxy and its stellar halo: insights on their formation from a hybrid cosmological approach
• The Hercules-Aquila Cloud
• The Shape and Profile of the Milky Way Halo as Seen by the CFHT Legacy Survey
• Light and Motion in SDSS Stripe 82: The Catalogues
• Stellar Population Variations in the Milky Way's Stellar Halo
• Exploring the Variable Sky with the Sloan Digital Sky Survey

Cited by in corpus (225)

• The Galaxy in Context: Structural, Kinematic and Integrated Properties
• Co-formation of the Galactic disc and the stellar halo
• Near-Field Cosmology with Metal-Poor Stars
• 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 Biggest Splash
• Cosmological simulations of the formation of the stellar haloes around disc galaxies
• Stellar Streams Discovered in the Dark Energy Survey
• The large-scale structure of the halo of the Andromeda Galaxy Part I: global stellar density, morphology and metallicity properties
• Sagittarius II, Draco II and Laevens 3: three new Milky Way satellites discovered in the Pan-STARRS 1 3pi Survey
• The Bifurcated Age-Metallicity Relation of Milky Way Globular Clusters and its Implications For the Accretion History of the Galaxy
• The Influence of Sagittarius and the Large Magellanic Cloud on the Milky Way Galaxy
• Precession of the Sagittarius stream
• Mass and shape of the Milky Way's dark matter halo with globular clusters from Gaia and Hubble
• On the Shoulders of Giants: Properties of the Stellar Halo and the Milky Way Mass Distribution
• The Sausage Globular Clusters
• The Milky Way's rotation curve out to 100 kpc and its constraint on the Galactic mass distribution
• The hidden giant: discovery of an enormous Galactic dwarf satellite in Gaia DR2
• Broken and unbroken: the Milky Way and M31 stellar haloes
• Kinematics of the stellar halo and the mass distribution of the Milky Way using BHB stars
• Contributions to the accreted stellar halo: an atlas of stellar deposition
• The Sagittarius Streams in the Southern Galactic Hemisphere
• Reconstructing the Last Major Merger of the Milky Way with the H3 Survey
• Halo Mass and Assembly History Exposed in the Faint Outskirts: the Stellar and Dark Matter Haloes of Illustris Galaxies
• Hydra II: a faint and compact Milky Way dwarf galaxy found in the Survey of the Magellanic Stellar History
• Ages and kinematics of chemically selected, accreted Milky Way halo stars
• Overview of the DESI Milky Way Survey
• Global structure and kinematics of stellar haloes in cosmological hydrodynamic simulations
• Formation of In Situ Stellar Haloes in Milky Way-Mass Galaxies
• The total stellar halo mass of the Milky Way
• The cold veil of the Milky Way stellar halo
• SMASH - Survey of the MAgellanic Stellar History
• Apocenter Pile-Up: Origin of the Stellar Halo Density Break
• The shape of the Galactic halo with $Gaia$ DR2 RR Lyrae. Anatomy of an ancient major merger
• The origin of galactic metal-rich stellar halo components with highly eccentric orbits
• Galactic Stellar Populations in the Era of SDSS and Other Large Surveys
• Diverse Stellar Haloes in Nearby Milky Way-Mass Disc Galaxies
• The mass of our Milky Way
• Piercing the Milky Way: an all-sky view of the Orphan Stream
• The radial profile and flattening of the Milky Way's stellar halo to $80$kpc from the SEGUE K-giant Survey
• The Southern Stellar Stream Spectroscopic Survey ($S^5$): Overview, Target Selection, Data Reduction, Validation, and Early Science
• Measuring the Mass of the Large Magellanic Cloud with Stellar Streams Observed by $S^5$
• Halo Substructure in the SDSS-Gaia Catalogue : Streams and Clumps
• The local high velocity tail and the Galactic escape speed
• Snake in the Clouds: A new nearby dwarf galaxy in the Magellanic bridge
• At the survey limits: discovery of the Aquarius 2 dwarf galaxy in the VST ATLAS and the SDSS data
• 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 Milky Way Halo in Action Space
• Exploring the Variable Sky with LINEAR. II. Halo Structure and Substructure Traced by RR Lyrae Stars to 30 kpc
• Discovery of $\sim$ 9,000 new RR Lyrae in the Southern Catalina Surveys
• Weighing the stellar constituents of the Galactic halo with APOGEE red giant stars
• Chemo-kinematics of the $Gaia$ RR Lyrae: the halo and the disc
• Galactic Archaeology. The dwarfs that survived and perished
• The Canada-France Imaging Survey: First results from the u-band component
• The ARTEMIS simulations: stellar haloes of Milky Way-mass galaxies
• The SEGUE K giant survey II: A Catalog of Distance Determinations for the SEGUE K giants in the Galactic Halo
• The Halo's Ancient Metal-Rich Progenitor Revealed with BHB Stars
• A Tail of Two Populations: Chemo-dynamics of the Sagittarius Stream and Implications for its Original Mass
• Touching The Void: A Striking Drop in Stellar Halo Density Beyond 50 kpc
• Stellar streams around the Magellanic Clouds
• The first all-sky view of the Milky Way stellar halo with Gaia+2MASS RR Lyrae
• The slight spin of the old stellar halo
• The global mass functions of 35 Galactic globular clusters: I. Observational data and correlations with cluster parameters
• The RAVE-on catalog of stellar atmospheric parameters and chemical abundances for chemo-dynamic studies in the Gaia era
• On the Run: mapping the escape speed across the Galaxy with SDSS
• Galactic Archaeology with Gaia
• La Silla QUEST RR Lyrae Star Survey: Region I
• Dark Shards: velocity substructure from Gaia and direct searches for dark matter
• Broken into Pieces: ATLAS and Aliqa Uma as One Single Stream
• Action-space clustering of tidal streams to infer the Galactic potential
• Tracing the Orphan Stream to 55 kpc with RR Lyrae Stars
• Common origin for Hercules-Aquila and Virgo Clouds in Gaia DR2
• Characterising stellar halo populations I: An extended distribution function for halo K giants
• The Pisces Plume and the Magellanic Wake
• The Stellar Halo of the Galaxy is Tilted & Doubly Broken
• The Edge of the Galaxy
• The Progenitors of the Milky Way Stellar Halo: Big Bricks Favoured over Little Bricks
• Boötes IV: A New Milky Way Satellite Discovered in the Subaru Hyper Suprime-Cam Survey and Implications for the Missing Satellite Problem
• Finding, characterizing and classifying variable sources in multi-epoch sky surveys: QSOs and RR Lyrae in PS1 3$\pi$ data
• The Velocity Anisotropy of Distant Milky Way Halo Stars from Hubble Space Telescope Proper Motions
• The Profile of the Galactic Halo from Pan-STARRS1 3$\pi$ RR Lyrae
• A stellar stream remnant of a globular cluster below the metallicity floor
• Mapping the Milky Way with LAMOST I: Method and overview
• The merger and assembly histories of Milky Way- and M31-like galaxies with TNG50: disk survival through mergers
• The Phoenix stream: a cold stream in the Southern hemisphere
• The Milky Way Tomography with SDSS. V. Mapping the Dark Matter Halo
• The Kinematic Properties of BHB and RR Lyrae stars towards the Anticentre and the North Galactic Pole: The Transition between the Inner and the Outer Halo
• 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
• TriAnd and its Siblings: Satellites of Satellites in the Milky Way Halo
• The Galactic Thick Disc density profile traced with RR Lyrae stars
• A-type stars in the Canada-France Imaging Survey I. The stellar halo of the Milky Way traced to large radius by blue horizontal branch stars
• The contribution of N-rich stars to the Galactic stellar halo using APOGEE red giants
• The Kinematic Properties of Milky Way Stellar Halo Populations
• Discovery of distant RR Lyrae stars in the Milky Way using DECam
• Stellar halo substructure generated by bar resonances
• Haloes light and dark: dynamical models of the stellar halo and constraints on the mass of the Galaxy
• Unmixing the Galactic Halo with RR Lyrae tagging
• A "Light," Centrally-Concentrated Milky Way Halo?
• The Pristine Dwarf-Galaxy survey - II. In-depth observational study of the faint Milky Way satellite Sagittarius II
• The dynamically selected stellar halo of the Galaxy with Gaia and the tilt of the velocity ellipsoid
• The age structure of the Milky Way's halo
• Characterizing stellar halo populations II: The age gradient in blue horizontal-branch stars
• Creating mock catalogues of stellar haloes from cosmological simulations
• The distribution of globular clusters in kinematic spaces does not trace the accretion history of the host galaxy
• Energy wrinkles and phase-space folds of the last major merger
• Strong RR Lyrae excess in the Hercules-Aquila Cloud
• Exploring the Very Extended Low Surface Brightness Stellar Populations of the Large Magellanic Cloud with SMASH
• The fall of the Northern Unicorn: Tangential motions in the Galactic Anti-centre with SDSS and Gaia
• Variable stars in the field of the Hydra II ultra-faint dwarf galaxy
• Milky Way Mass with K Giants and BHB Stars Using LAMOST, SDSS/SEGUE, and Gaia: 3D Spherical Jeans Equation and Tracer Mass Estimator
• Probing the galactic halo with RR Lyrae stars I: The catalog
• The Milky Way's Shell Structure Reveals the Time of a Radial Collision
• Metallicity Bias in the Kinematics of the Milky Way Stellar Halo
• A Tale Twice Told: The Luminosity Profiles of the Sagittarius Tails
• The Saga of M81: Global View of a Massive Stellar Halo in Formation
• A skewer survey of the Galactic halo from deep CFHT and INT images
• The Nature of Ionized Gas in the Milky Way Galactic Fountain
• The Complexity of the Cetus Stream Unveiled from the Fusion of STREAMFINDER and StarGO
• The SEGUE K Giant Survey. III. Quantifying Galactic Halo Substructure
• Mapping the Milky Way with LAMOST II: the stellar halo
• Chronography of the Milky Way's Halo System with Field Blue Horizontal-Branch Stars
• Is the Dark Halo of the Milky Way Prolate?
• Two Thresholds for Globular Cluster Formation and their Dominance of Star Formation in the Early-Universe
• The Outer Halo of the Milky Way as Probed by RR Lyr Variables from the Palomar Transient Facility
• Identifying RR Lyrae Variable Stars in Six Years of the Dark Energy Survey
• HALO7D II: The Halo Velocity Ellipsoid and Velocity Anisotropy with Distant Main Sequence Stars
• Estimating the selection function of Gaia DR3 sub-samples
• The hidden past of M92: Detection and characterization of a newly formed 17° long stellar stream using the Canada-France Imaging Survey
• Radial halo substructure in harmony with the Galactic bar
• The stellar halo of the Milky Way traced by blue horizontal-branch stars in the Subaru Hyper Suprime-Cam Survey
• Stellar Velocity Dispersion and Anisotropy of the Milky Way Inner Halo
• The Frequency of Field Blue-Straggler Stars in the Thick Disk and Halo System of the Galaxy
• Stellar chemo-kinematics of the Cetus dwarf spheroidal galaxy
• RR Lyrae in XSTPS: The halo density profile in the North Galactic Cap
• Stellar halos from The Dragonfly Edge-on Galaxies Survey
• Mapping the anisotropic Galactic stellar halo with Blue Horizontal Branch stars
• To the Galactic Virial Radius with Hyper Suprime-Cam
• VINTERGATAN-GM: The cosmological imprints of early mergers on Milky-Way-mass galaxies
• Rotational signature of the Milky Way stellar halo
• Isotropic at the Break? 3D Kinematics of Milky Way Halo Stars in the Foreground of M31
• The Pristine survey -- VII. A cleaner view of the Galactic outer halo using blue horizontal branch stars
• The stellar halo in Local Group Hestia simulations I. The in-situ component and the effect of mergers
• Galactic Gas Flows from Halo to Disk: Tomography and Kinematics at the Milky Way's Disk-Halo Interface
• The Stellar Density Profile of the Distant Galactic Halo
• A Swing of the Pendulum: The Chemodynamics of the Local Stellar Halo Indicate Contributions from Several Radial Merger Events
• Discovery of a new Local Group Dwarf Galaxy Candidate in UNIONS: Boötes V
• The observable properties of galaxy accretion events in Milky Way-like galaxies in the FIRE-2 cosmological simulations
• Structure of the Milky Way stellar halo out to its outer boundary with blue horizontal-branch stars
• The stretching of Hercules
• Quantifying the Smoothness of the Stellar Halo: A Link to Accretion History
• The Cetus-Palca stream: A disrupted small dwarf galaxy. A prequel to the science possible with WEAVE with precise spectro-photometric distances
• Two Distant Halo Velocity Groups Discovered by the Palomar Transient Factory
• A new calibration for the Blue Horizontal Branch
• Update on the Cetus Polar Stream and its Progenitor
• Chemical Mapping of the Milky Way With The Canada-France Imaging Survey: A Non-parametric Metallicity-Distance Decomposition of the Galaxy
• Galactic googly: the rotation-metallicity bias in the inner stellar halo of the Milky Way
• A-type stars in the Canada-France Imaging Survey II. Tracing the height of the disc at large distances with Blue Stragglers
• Modelling the Milky Way. I -- Method and first results fitting the thick disk and halo with DES-Y3 data
• Clean catalogues of blue horizontal-branch stars using Gaia EDR3
• HALO7D I: The Line of Sight Velocities of Distant Main Sequence Stars in the Milky Way Halo
• Unearthing Foundations of a Cosmic Cathedral: Searching the Stars for M33's Halo
• On the Use of Field RR Lyrae as Galactic Probes. V. Optical and radial velocity curve templates
• The course of the Orphan Stream in the Northern Galactic Hemisphere traced with Gaia DR2
• The Panchromatic Hubble Andromeda Treasury II. Tracing the Inner M31 Halo with Blue Horizontal Branch Stars
• DELVE-ing into the Jet: a thin stellar stream on a retrograde orbit at 30 kpc
• A LAMOST BHB Catalog and Kinematics Therein I: Catalog and Halo Properties
• The metal-rich halo component extended in z: a characterization with Gaia DR2 and APOGEE
• Population III stars around the Milky Way
• Modelling the stellar halo with RR-Lyrae stars
• Exploring the interaction between the MW and LMC with a large sample of blue horizontal branch stars from the DESI survey
• The QuaStar Survey: Detecting Hidden Low-Velocity Gas in the Milky Way's Circumgalactic Medium
• Constraints on the Galactic Inner Halo Assembly History from the Age Gradient of Blue Horizontal-branch Stars
• Uncovering fossils of the distant Milky Way with UNIONS: NGC 5466 and its stellar stream
• Inferring the Morphology of Stellar Distribution in TNG50: Twisted and Twisted-Stretched shapes
• A Very Simple Cusped Halo Model
• An extended view of the Pisces Overdensity from the SCUSS survey
• Discovery of a thin stellar stream in the SLAMS survey
• Stellar streams around the Magellanic Clouds in 4D
• The SDSS-Gaia View of the Color-Magnitude Relation for Blue Horizontal-branch Stars
• Reliability of the measured velocity anisotropy of the Milky Way stellar halo
• The Photo-Astrometric Vertical Tracer Density of the Milky Way II: Results from Gaia
• Spectroscopic Follow-Up of the Hercules Aquila Cloud
• A 10,000 star spectroscopic survey of the thick disk-halo interface : Phase-space sub-structure in the thick disk
• The Early Merger that Made the Galaxy's Stellar Halo
• Influence of the Gaia-Sausage-Enceladus on the density shape of the Galactic stellar halo revealed by halo K giants from the LAMOST survey
• Virial Sequences for Thick Discs and Haloes: Flattening and Global Anisotropy
• The Reduced Proper Motion selected halo: methods and description of the catalogue
• Tilted outer and inner structures in edge-on galaxies?
• Observing the stellar halo of Andromeda in cosmological simulations: the Auriga2PAndAS pipeline
• Hidden deep in the halo: selection of a reduced proper motion halo catalogue and mining retrograde streams in the velocity space
• The Density Profile and Kinematics of the Milky Way with RR Lyrae Stars
• An optimized Method to Identify RR Lyrae stars in the SDSS X Pan-STARRS1 Overlapping Area Using a Bayesian Generative Technique
• A Stellar Population Synthesis Model for the Study of Ultraviolet Star Counts of the Galaxy
• Existence of the Metal-Rich Stellar Halo and High-velocity Thick Disk in the Galaxy
• L-GALAXIES 2020: The formation and chemical evolution of stellar haloes in Milky Way Analogues and galaxy clusters
• Low-metallicity stellar halo populations as tracers of dark matter haloes
• Resolved Stellar Populations as Tracers of Outskirts
• Fading Features Found in the Kinematics of the Far-Reaching Milky Way Stellar Halo
• A Pristine-UNIONS view on the Galaxy: Kinematics of the distant spur feature of the Sagittarius stream traced by Blue Horizontal Branch stars
• A Ghost in Boötes: The Least Luminous Disrupted Dwarf Galaxy
• HALO7D III: Chemical Abundances of Milky Way Halo Stars from Medium Resolution Spectra
• Mapping the Milky Way's stellar halo with 2D data
• The Doubloon Models of Dark Haloes
• The Pristine Survey -- XXVII. Journey to the Galactic outskirts -- Mapping the outer halo red giant stars down to the very metal-poor end
• Determining the Scale Length and Height of the Milky Way's Thick Disc Using RR~Lyrae
• AuriDESI: Mock Catalogues for the DESI Milky Way Survey
• Mapping Milky Way Halo Substructure using Stars in the Extended Blue Tail of the Horizontal Branch
• First resolved stellar halo kinematics of a MW-mass galaxy outside the Local Group: A flat counter-rotating halo in NGC 4945
• Discovery of the shell structure via break radii in the outer halo of the Milky Way
• Galactic cartography with SkyMapper: I. Population sub-structure and the stellar number density of the inner halo
• An Orbit Fit to Likely Hermus Stream Stars
• A fork in the Sagittarius trailing debris
• Tomography of stellar halos: what does anisotropy in a stellar halo tell us?
• Studying stellar halos with future facilities
• Segue 2 Recently Collided with the Cetus-Palca Stream: New Opportunities to Constrain Dark Matter in an Ultra-Faint Dwarf
• Supernova explosions of runaway stars and young neutron stars above the Galactic plane
• Stellar halo striations from assumptions of axisymmetry
• High resolution observations of Cen A: Yellow and red supergiants in a region of jet-induced star formation?
• On the Origins of "Hostless'' Supernovae: Testing the Faint-end Galaxy Luminosity Function and Supernova Progenitors with Events in Dwarf Galaxies
• Probing the spatial and velocity anisotropies in stellar halos from the Aquarius simulations
• Smart: A program to automatically compute accelerations and variational equations
• rrlfe: Software for Generating and Applying Metallicity Calibrations for RR Lyrae Variable Stars Across a Wide Range of Phases and Temperatures
• Constraining the shape of Milky Way satellites with distance gradients