Mapping the anisotropic Galactic stellar halo with Blue Horizontal Branch stars

Abstract

We use Legacy Survey photometric data to probe the stellar halo in multiple directions of the sky using a probabilistic methodology to identify Blue Horizontal Branch (BHB) stars. The measured average radial density profile follows a double power law in the range $5<r_{gc}/\mathrm{kpc}<120$, with a density break at $r_{gc}\approx 20$ kpc. This description, however, falls short, depending on the chosen line-of-sight, with some regions showing no signature of a break in the profile and a wide range of density slopes, e.g. outer slope $-5.5\lesssim {\alpha }_{out}\lesssim -4$, pointing towards a highly anisotropic stellar halo. This explains in part the wide range of density profiles reported in the literature owing to different tracers and sky coverage. Using our detailed 3-D stellar halo density map, we quantify the shape of the Pisces overdensity associated with the transient wake response of the Galaxy's (dark) halo to the Large Magellanic Cloud (LMC). Measured in the LMC's coordinate system, Pisces stands above the background, is 60 degrees long and 25 degrees wide and aligned with the LMC's orbit. This would correspond to a wake width of $\sim 32$ kpc at $\sim 70$ kpc. We do not find a statistically significant signature of the collective response in density as previously reported in the literature measured with K giant stars, despite our larger numbers. We release the catalogue constructed in this study with 95,446 possible BHB stars and their BHB probability.

arXiv commentAccepted for publication in A&A. The catalogue can be found here: https://zenodo.org/records/12155488

References in corpus (124)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• emcee: The MCMC Hammer
• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• HEALPix -- a Framework for High Resolution Discretization, and Fast Analysis of Data Distributed on the Sphere
• The observed properties of dwarf galaxies in and around the Local Group
• Overview of the DESI Legacy Imaging Surveys
• The Milky Way Tomography with SDSS: I. Stellar Number Density Distribution
• The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
• The mass distribution and gravitational potential of the Milky Way
• Tracing Galaxy Formation with Stellar Halos I: Methods
• Co-formation of the Galactic disc and the stellar halo
• Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way Companions
• The large-scale structure of the Universe
• The Ghost of Sagittarius and Lumps in the Halo of the Milky Way
• Kinematics of Metal-Poor Stars in the Galaxy. III. Formation of the Stellar Halo and Thick Disk as Revealed from a Large Sample of Non-Kinematically Selected Stars
• Debris streams in the solar neighbourhood as relicts from the formation of the Milky Way
• Are the Magellanic Clouds on their First Passage about the Milky Way?
• AGAMA: Action-based galaxy modelling architecture
• Beasts of the Southern Wild: Discovery of nine Ultra Faint satellites in the vicinity of the Magellanic Clouds
• Near-Field Cosmology with Metal-Poor Stars
• The ACS Survey of Galactic Globular Clusters. IX. Horizontal Branch Morphology and the Second Parameter Phenomenon
• The accretion origin of the Milky Way's stellar halo
• Vertical waves in the solar neighbourhood in Gaia DR2
• Origin of the system of globular clusters in the Milky Way
• Tracing Galaxy Formation with Stellar Halos II: Relating Substructure in Phase- and Abundance-Space to Accretion Histories
• Identification of A-colored Stars and Structure in the Halo of the Milky Way from SDSS Commissioning Data
• Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure
• In disguise or out of reach: first clues about in-situ and accreted stars in the stellar halo of the Milky Way from Gaia DR2
• A catalogue of white dwarfs in Gaia EDR3
• The SDSS-III Baryon Oscillation Spectroscopic Survey: Quasar Target Selection for Data Release Nine
• The Milky Way stellar halo out to 40 kpc : Squashed, broken but smooth
• Footprints of the Sagittarius dwarf galaxy in the $Gaia$ data set
• Substructure revealed by RR Lyraes in SDSS Stripe 82
• The Disruption of the Sagittarius Dwarf Galaxy.
• The birth of the Milky Way as uncovered by accurate stellar ages with Gaia
• The Sagittarius impact as an architect of spirality and outer rings in the Milky Way
• Multiple retrograde substructures in the Galactic halo: A shattered view of Galactic history
• A time-resolved picture of our Milky Way's early formation history
• The Influence of Sagittarius and the Large Magellanic Cloud on the Milky Way Galaxy
• Vertical density waves in the Milky Way disc induced by the Sagittarius Dwarf Galaxy
• The QUEST RR Lyrae Survey: Confirmation of the Clump at 50 kpc and Other Over-Densities in the Outer Halo
• Light Curve Templates and Galactic Distribution of RR Lyrae Stars from Sloan Digital Sky Survey Stripe 82
• Precession of the Sagittarius stream
• The Sausage Globular Clusters
• Hunting for the Dark Matter Wake Induced by the Large Magellanic Cloud
• Broken and unbroken: the Milky Way and M31 stellar haloes
• And yet it moves: The dangers of artificially fixing the Milky Way center of mass in the presence of a massive Large Magellanic Cloud
• Quantifying Kinematic Substructure in the Milky Way's Stellar Halo
• The Hercules-Aquila Cloud
• Deciphering The Last Major Invasion of the Milky Way Galaxy
• Machine-Learned Identification of RR Lyrae Stars from Sparse, Multi-band Data: the PS1 Sample
• The Global Dynamical Atlas of the Milky Way mergers: Constraints from Gaia EDR3 based orbits of globular clusters, stellar streams and satellite galaxies
• Reconstructing the Last Major Merger of the Milky Way with the H3 Survey
• Reverse engineering the Milky Way
• Ages and kinematics of chemically selected, accreted Milky Way halo stars
• Blue horizontal branch stars in the Sloan Digital Sky Survey: I. Sample selection and structure in the Galactic halo
• Dynamical Relics of the Ancient Galactic Halo
• Accretion relicts in the solar neighbourhood: debris from omegaCen's parent galaxy
• The total stellar halo mass of the Milky Way
• Response of the Milky Way's disc to the Large Magellanic Cloud in a first infall scenario
• Chronologically dating the early assembly of the Milky Way
• 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
• Proper Motions, Orbits, and Tidal Influences of Milky Way Dwarf Spheroidal Galaxies
• All-Sky Dynamical Response of the Galactic Halo to the Large Magellanic Cloud
• The SkyMapper-Gaia RVS view of the Gaia-Enceladus-Sausage -- an investigation of the metallicity and mass of the Milky Way's last major merger
• A Magellanic Origin for the Warp of the Galaxy
• Detection of the Milky Way reflex motion due to the Large Magellanic Cloud infall
• Detection of the LMC-induced sloshing of the Galactic halo
• Touching The Void: A Striking Drop in Stellar Halo Density Beyond 50 kpc
• Reconstructing the Disrupted Dwarf Galaxy $Gaia$-Sausage/Enceladus Using its Stars and Globular Clusters
• Stellar streams around the Magellanic Clouds
• The first all-sky view of the Milky Way stellar halo with Gaia+2MASS RR Lyrae
• A large accretion disk of extreme eccentricity in the TDE ASASSN-14li
• Galactic Halo Stars in Phase Space :A Hint of Satellite Accretion?
• Reflex motion in the Milky Way stellar halo resulting from the Large Magellanic Cloud infall
• La Silla QUEST RR Lyrae Star Survey: Region I
• GASTRO library I: the simulated chemodynamical properties of several GSE-like stellar halos
• The effect of the LMC on the Milky Way system
• The $>100$ kpc Distant Spur of the Sagittarius Stream and the Outer Virgo Overdensity, as Seen in PS1 RR Lyrae Stars
• Evidence from Disrupted Halo Dwarfs that $r$-process Enrichment via Neutron Star Mergers is Delayed by $\gtrsim 500$ Myrs
• The Geometry of Sagittarius Stream from Pan-STARRS1 3$\pi$ RR Lyrae
• Dynamically Tagged Groups of Very Metal-poor Halo Stars from the HK and Hamburg/ESO Surveys
• Common origin for Hercules-Aquila and Virgo Clouds in Gaia DR2
• Stellar Population Variations in the Milky Way's Stellar Halo
• Six More Ultra-Faint Milky Way Companions Discovered in the DECam Local Volume Exploration Survey
• The Pisces Plume and the Magellanic Wake
• The Stellar Halo of the Galaxy is Tilted & Doubly Broken
• The Profile of the Galactic Halo from Pan-STARRS1 3$\pi$ RR Lyrae
• Quantifying the Stellar Halo's Response to the LMC's Infall with Spherical Harmonics
• The tale of the tail -- disentangling the high transverse velocity stars in Gaia DR2
• 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
• Discovery of distant RR Lyrae stars in the Milky Way using DECam
• Identifying Blue Horizontal Branch Stars Using the z Filter
• Strong RR Lyrae excess in the Hercules-Aquila Cloud
• The Milky Way's Shell Structure Reveals the Time of a Radial Collision
• Update on the Nature of Virgo Overdensity
• A skewer survey of the Galactic halo from deep CFHT and INT images
• The Clustering of Orbital Poles Induced by the LMC: Hints for the Origin of Planes of Satellites
• Chronography of the Milky Way's Halo System with Field Blue Horizontal-Branch Stars
• The star cluster age function in the Galactic disc with Gaia DR2: Fewer old clusters and a low cluster formation efficiency
• Discovery of the Magellanic Stellar Stream Out to 100 Kiloparsecs
• Identifying RR Lyrae Variable Stars in Six Years of the Dark Energy Survey
• Migration and Mixing in the Galactic Disc from Encounters between Sagittarius and the Milky Way
• The stellar halo of the Milky Way traced by blue horizontal-branch stars in the Subaru Hyper Suprime-Cam Survey
• Distant Echoes of the Milky Way's Last Major Merger
• Spectroscopic Confirmation of the Pisces Overdensity
• To the Galactic Virial Radius with Hyper Suprime-Cam
• The Pristine survey -- VII. A cleaner view of the Galactic outer halo using blue horizontal branch stars
• A Swing of the Pendulum: The Chemodynamics of the Local Stellar Halo Indicate Contributions from Several Radial Merger Events
• The Unmixed Debris of Gaia-Sausage/Enceladus in the Form of a Pair of Halo Stellar Overdensities
• Structure of the Milky Way stellar halo out to its outer boundary with blue horizontal-branch stars
• Contribution of Gaia Sausage to the Galactic Stellar Halo Revealed by K Giants and Blue Horizontal Branch Stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, Sloan Digital Sky Survey, and Gaia
• Exploring the diversity and similarity of radially anisotropic Milky Way-like stellar haloes: implications for disrupted dwarf galaxy searches
• Probing the Galactic halo with RR Lyrae stars $-$ III. The chemical and kinematic properties of the stellar halo
• Modelling the Milky Way. I -- Method and first results fitting the thick disk and halo with DES-Y3 data
• Tidally stripped halo stars from the Large Magellanic Cloud in the Galactic North
• An extended view of the Pisces Overdensity from the SCUSS survey
• Constructing the Milky Way Stellar Halo in the Galactic Center by Direct Orbit Integration
• Local Group Dwarf Galaxy Detection Limit in the CSST survey
• The SDSS-Gaia View of the Color-Magnitude Relation for Blue Horizontal-branch Stars
• Exploring the chemodynamics of metal-poor stellar populations
• Influence of the Gaia-Sausage-Enceladus on the density shape of the Galactic stellar halo revealed by halo K giants from the LAMOST survey
• Identifying RR Lyrae in the ZTF DR3 dataset

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• All-Sky Kinematics of the Distant Halo: The Reflex Response to the LMC
• Shaping the Milky Way: The interplay of mergers and cosmic filaments
• A Pristine-UNIONS view on the Galaxy: Kinematics of the distant spur feature of the Sagittarius stream traced by Blue Horizontal Branch stars
• Following the tidal trail: a history of modeling the Magellanic Stream
• A Simulation Based Inference Approach to the Dynamics of the MW-LMC System -- Validation
• Dark matter spiral arms in Milky Way-like halos
• Quantifying the Milky Way, LMC and their interaction using all-sky kinematics of outer halo stars
• Searching for stars ejected from the Galactic Centre in DESI
• Mapping the Distorted Dark Matter Distribution of the LMC-SMC System Prior to Milky Way Infall with Basis Function Expansions
• Epicyclic Density Variations in the Indus Stellar Stream
• A comparative study of O, Ne, Cl, and Ar in Hii regions and PNe of the Galactic disk: Temporal evolution of radial gradients?