Touching The Void: A Striking Drop in Stellar Halo Density Beyond 50 kpc

Abstract

We use A-type stars selected from Sloan Digital Sky Survey data release 9 photometry to measure the outer slope of the Milky Way stellar halo density profile beyond 50 kpc. A likelihood-based analysis is employed that models the ugr photometry distribution of blue horizontal branch (BHB) and blue straggler (BS) stars. In the magnitude range, 18.5 < g < 20.5, these stellar populations span a heliocentric distance range of: 10 kpc < D_BS < 75 kpc, 40 kpc < D_BHB < 100 kpc. Contributions from contaminants, such as QSOs, and the effect of photometric uncertainties, are also included in our modeling procedure. We find evidence for a very steep outer halo profile, with power-law index alpha ~ 6 beyond Galactocentric radii r=50 kpc, and even steeper slopes favored (alpha ~ 6-10) at larger radii. This result holds true when stars belonging to known overdensities, such as the Sagittarius stream, are included or excluded. We show that, by comparison to numerical simulations, stellar halos with shallower slopes at large distances tend to have more recent accretion activity. Thus, it is likely that the Milky Way has undergone a relatively quiet accretion history over the past several Gyr. Our measurement of the outer stellar halo profile may have important implications for dynamical mass models of the Milky Way, where the tracer density profile is strongly degenerate with total mass-estimates.

arXiv comment17 pages, 16 figures. Accepted for publication by ApJ. References updated

References in corpus (63)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• The Sloan Digital Sky Survey: Technical Summary
• A Universal Density Profile from Hierarchical Clustering
• The 2.5 m Telescope of the Sloan Digital Sky Survey
• The Sloan Digital Sky Survey Photometric Camera
• The u'g'r'i'z' Standard Star Network
• The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey
• The Milky Way Tomography with SDSS: I. Stellar Number Density Distribution
• Tracing Galaxy Formation with Stellar Halos I: Methods
• The Field of Streams: Sagittarius and its Siblings
• Astrometric Calibration of the Sloan Digital Sky Survey
• Reionization and the abundance of galactic satellites
• The Ghost of Sagittarius and Lumps in the Halo of the Milky Way
• 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
• The RAVE Survey: Constraining the Local Galactic Escape Speed
• Two Stellar Components in the Halo of the Milky Way
• Two distinct halo populations in the solar neighborhood. Evidence from stellar abundance ratios and kinematics
• Forming Realistic Late-Type Spirals in a LCDM Universe: The Eris Simulation
• Structure and Kinematics of the Stellar Halos and Thick Disks of the Milky Way Based on Calibration Stars from SDSS DR7
• Third-Epoch Magellanic Cloud Proper Motions I: HST/WFC3 data and Orbit Implications
• An Improved Spectroscopic Analysis of DA White Dwarfs from the Sloan Digital Sky Survey Data Release 4
• The accretion origin of the Milky Way's stellar halo
• Can Photoionization Squelching Resolve the Sub-structure Crisis?
• The Milky Way's circular velocity curve between 4 and 14 kpc from APOGEE data
• Identification of A-colored Stars and Structure in the Halo of the Milky Way from SDSS Commissioning Data
• The Present and Future Mass of the Milky Way Halo
• Sagittarius: The Nearest Dwarf Galaxy
• The Masses of the Milky Way and Andromeda galaxies
• A Comprehensive Spectroscopic Analysis of DB White Dwarfs
• The Milky Way stellar halo out to 40 kpc : Squashed, broken but smooth
• The radial velocity dispersion profile of the Galactic halo: Constraining the density profile of the dark halo of the Milky Way
• Found: The missing blue opacity in atmosphere models of cool hydrogen white dwarfs
• The large-scale structure of the halo of the Andromeda Galaxy Part I: global stellar density, morphology and metallicity properties
• Substructure revealed by RR Lyraes in SDSS Stripe 82
• The M31 Velocity Vector. II. Radial Orbit Towards the Milky Way and Implied Local Group Mass
• Masses for the Local Group and the Milky Way
• Precession of the Sagittarius stream
• Think Outside the Color Box: Probabilistic Target Selection and the SDSS-XDQSO Quasar Targeting Catalog
• The Space Motion of Leo I: The Mass of the Milky Way's Dark Matter Halo
• Broken and unbroken: the Milky Way and M31 stellar haloes
• The Case for the Dual Halo of the Milky Way
• The Hercules-Aquila Cloud
• The Shape and Profile of the Milky Way Halo as Seen by the CFHT Legacy Survey
• Galactic Globular and Open Clusters in the Sloan Digital Sky Survey. I. Crowded Field Photometry and Cluster Fiducial Sequences in ugriz
• Blue horizontal branch stars in the Sloan Digital Sky Survey: I. Sample selection and structure in the Galactic halo
• The cold veil of the Milky Way stellar halo
• The velocity dispersion and mass profile of the Milky Way
• The Space Motion of Leo I: Hubble Space Telescope Proper Motion and Implied Orbit
• First results from the Dragonfly Telephoto Array: the apparent lack of a stellar halo in the massive spiral galaxy M101
• Global Properties of M31's Stellar Halo from the SPLASH Survey. I. Surface Brightness Profile
• On the alleged duality of the Galactic halo
• Velocity Dispersion Profile of the Milky Way Halo
• Distant field BHB stars and the mass of the Galaxy I: Classification of halo A-type stars
• On the mass of the Local Group
• The Velocity Anisotropy of Distant Milky Way Halo Stars from Hubble Space Telescope Proper Motions
• Testing galaxy formation models with the GHOSTS survey: The color profile of M81's stellar halo
• A "Light," Centrally-Concentrated Milky Way Halo?
• A panoramic VISTA of the stellar halo of NGC 253
• Very Metal-Poor Outer-Halo Stars with Round Orbits
• Does SEGUE/SDSS indicate a dual Galactic halo?
• Metallicity Bias in the Kinematics of the Milky Way Stellar Halo
• Disentangling the dark matter halo from the stellar halo
• Rotational signature of the Milky Way stellar halo

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• The Galaxy in Context: Structural, Kinematic and Integrated Properties
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• On the Shoulders of Giants: Properties of the Stellar Halo and the Milky Way Mass Distribution
• The SDSS Coadd: 275 deg^2 of Deep SDSS Imaging on Stripe 82
• Hunting for the Dark Matter Wake Induced by the Large Magellanic Cloud
• Contributions to the accreted stellar halo: an atlas of stellar deposition
• Reconstructing the Last Major Merger of the Milky Way with the H3 Survey
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• Characterising stellar halo populations I: An extended distribution function for halo K giants
• The Stellar Halo of the Galaxy is Tilted & Doubly Broken
• The Edge of the Galaxy
• Quasar Probabilities and Redshifts from WISE mid-IR through GALEX UV Photometry
• The Profile of the Galactic Halo from Pan-STARRS1 3$\pi$ RR Lyrae
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• A search for stellar tidal debris of defunct dwarf galaxies around globular clusters in the inner Galactic halo
• TriAnd and its Siblings: Satellites of Satellites in the Milky Way Halo
• 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
• Constraining Milky Way mass with Hypervelocity Stars
• Discovery of distant RR Lyrae stars in the Milky Way using DECam
• A Gaia DR 2 and VLT/FLAMES search for new satellites of the LMC
• Probing the galactic halo with RR Lyrae stars I: The catalog
• Mapping the Milky Way with LAMOST II: the stellar halo
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• 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
• The stellar halo of the Milky Way traced by blue horizontal-branch stars in the Subaru Hyper Suprime-Cam Survey
• Hubble Space Telescope Proper Motions along the Sagittarius Stream: I. Observations and Results for Stars in Four Fields
• Mapping the anisotropic Galactic stellar halo with Blue Horizontal Branch stars
• Cosmological insights into the assembly of the radial and compact stellar halo of the Milky Way
• VINTERGATAN-GM: The cosmological imprints of early mergers on Milky-Way-mass galaxies
• The Pristine survey -- VII. A cleaner view of the Galactic outer halo using blue horizontal branch stars
• To the Galactic Virial Radius with Hyper Suprime-Cam
• The Stellar Density Profile of the Distant Galactic Halo
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• A-type stars in the Canada-France Imaging Survey II. Tracing the height of the disc at large distances with Blue Stragglers
• An enquiry on the origins of N-rich stars in the inner Galaxy basedon APOGEE chemical compositions
• A Very Simple Cusped Halo Model
• The elusive stellar halo of the Triangulum Galaxy
• The Photo-Astrometric Vertical Tracer Density of the Milky Way II: Results from Gaia
• Spectroscopic Follow-Up of the Hercules Aquila Cloud
• A Megacam Survey of Outer Halo Satellites. IV. Two foreground populations possibly associated with the Monoceros substructure in the direction of NGC2419 and Koposov2
• The Photo-Astrometric Vertical Tracer Density of the Milky Way I: The Method
• 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
• The Doubloon Models of Dark Haloes
• Mapping the Milky Way's stellar halo with 2D data
• Building Blocks of the Milky Way's Accreted Spheroid
• Discovery of the shell structure via break radii in the outer halo of the Milky Way
• Tomography of stellar halos: what does anisotropy in a stellar halo tell us?
• A fork in the Sagittarius trailing debris
• The Outer Galactic Halo As Probed By RR Lyr Stars From the Palomar Transient Facility + Keck
• A "Universal" Density Profile for the Outer Stellar Halos of Galaxies
• H$\alpha$ emission in the outskirts of galaxies at z=0.4
• Stellar halos of bright central galaxies II: Scaling relations, colors and metallicity evolution with redshift
• photoD with Rubin's Data Preview 1: first stellar photometric distances and deficit of faint blue stars. Stellar distances with Rubin's DP1