The Outer Halo of the Milky Way as Probed by RR Lyr Variables from the Palomar Transient Facility

Abstract

RR Lyr stars are ideal massless tracers that can be used to study the total mass and dark matter content of the outer halo of the Milky Way. This is because they are easy to find in the light curve databases of large stellar surveys and their distances can be determined with only knowledge of the light curve. We present here a sample of 112 RR Lyr beyond 50 kpc in the outer halo of the Milky Way, excluding the Sgr streams, for which we have obtained moderate resolution spectra with Deimos on the Keck 2 Telescope. Four of these have distances exceeding 100 kpc. These were selected from a much larger set of 447 candidate RR Lyr which were datamined using machine learning techniques applied to the light curves of variable stars in the Palomar Transient Facility database. The observed radial velocities taken at the phase of the variable corresponding to the time of observation were converted to systemic radial velocities in the Galactic standard of rest. From our sample of 112 RR Lyr we determine the radial velocity dispersion in the outer halo of the Milky Way to be ~90 km/s at 50 kpc falling to about 65 km/s near 100 kpc once a small number of major outliers are removed. With reasonable estimates of the completeness of our sample of 447 candidates and assuming a spherical halo, we find that the stellar density in the outer halo declines as the -4 power of r.

Accepted for publication in the ApJ

References in corpus (24)

• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• 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 Catalina Surveys Periodic Variable Star Catalog
• On the Shoulders of Giants: Properties of the Stellar Halo and the Milky Way Mass Distribution
• The Chemical Evolution of the Draco Dwarf Spheroidal Galaxy
• The shape of the inner Milky Way halo from observations of the Pal 5 and GD-1 stellar streams
• A Map of Dust Reddening to 4.5 kpc from Pan-STARRS1
• Discovery of $\sim$ 9,000 new RR Lyrae in the Southern Catalina Surveys
• Automatic Classification of Kepler Planetary Transit Candidates
• Evidence for Distinct Components of the Galactic Stellar Halo from 838 RR Lyrae Stars Discovered in the LONEOS-I Survey
• On the distance of the globular cluster M4 (NGC 6121) using RR Lyrae stars: I. optical and near-infrared Period-Luminosity and Period-Wesenheit relations
• Touching The Void: A Striking Drop in Stellar Halo Density Beyond 50 kpc
• Revealing Substructure in the Galactic Halo - The SEKBO RR Lyrae Survey
• Spectroscopic Comparison of Metal-Rich RRab Stars of the Galactic Field with Their Metal-Poor Counterparts
• The meaning of WISE colours - I. The Galaxy and its satellites
• The $>100$ kpc Distant Spur of the Sagittarius Stream and the Outer Virgo Overdensity, as Seen in PS1 RR Lyrae Stars
• Predicted Extension of the Sagittarius Stream to the Milky Way Virial Radius
• IPAC Image Processing and Data Archiving for the Palomar Transient Factory
• Stacking the Invisibles: A Guided Search for Low-Luminosity Milky Way Satellites
• Supervised detection of anomalous light-curves in massive astronomical catalogs
• The Period-Luminosity Relation of RR Lyrae Stars in the SDSS Photometric System
• The Stellar Density Profile of the Distant Galactic Halo
• The Most Distant Stars in the Milky Way
• Gamma/hadron segregation for a ground based imaging atmospheric Cherenkov telescope using machine learning methods: Random Forest leads

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• The Zwicky Transient Facility: System Overview, Performance, and First Results
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• Milky Way Mass with K Giants and BHB Stars Using LAMOST, SDSS/SEGUE, and Gaia: 3D Spherical Jeans Equation and Tracer Mass Estimator
• The stellar halo of the Milky Way traced by blue horizontal-branch stars in the Subaru Hyper Suprime-Cam Survey
• 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
• Structure, Kinematics, and Observability of the Large Magellanic Cloud's Dynamical Friction Wake in Cold vs. Fuzzy Dark Matter
• Exploring the diversity and similarity of radially anisotropic Milky Way-like stellar haloes: implications for disrupted dwarf galaxy searches
• Morphological Star-Galaxy Separation
• The Photo-Astrometric Vertical Tracer Density of the Milky Way II: Results from Gaia
• LMC-driven anisotropic boosts in stream--subhalo interactions
• Measuring the mass and concentration of dark matter halos from the velocity dispersion profile of their stars
• The Pristine Survey -- XXVII. Journey to the Galactic outskirts -- Mapping the outer halo red giant stars down to the very metal-poor end
• rrlfe: Software for Generating and Applying Metallicity Calibrations for RR Lyrae Variable Stars Across a Wide Range of Phases and Temperatures