The Far-Away Blues: Exploring the Furthest Extents of the Boötes I Ultra Faint Dwarf Galaxy

Abstract

Establishing the spatial extents and the nature of the outer stellar populations of dwarf galaxies are necessary ingredients for the determination of their total masses, current dynamical states and past evolution. We here describe our investigation of the outer stellar content of the Boötes I ultra-faint dwarf galaxy, a satellite of the Milky Way Galaxy. We identify candidate member blue horizontal branch and blue straggler stars of Boötes I, both tracers of the underlying ancient stellar population, using a combination of multi-band Pan-STARRS photometry and Gaia astrometry. We find a total of twenty-four candidate blue horizontal branch member stars with apparent magnitudes and proper motions consistent with membership of Boötes I, nine of which reside at projected distances beyond the nominal King profile tidal radius derived from earlier fits to photometry. We also identify four blue straggler stars of appropriate apparent magnitude to be at the distance of Boötes I, but all four are too faint to have high-quality astrometry from Gaia. The outer blue horizontal branch stars that we have identified confirm that the spatial distribution of the stellar population of Boötes I is quite extended. The morphology on the sky of these outer envelope candidate member stars is evocative of tidal interactions, a possibility that we explore further with simple dynamical models.

arXiv comment26 pages, 13 figures. Accepted for publication in ApJ

References in corpus (71)

• Astropy: A Community Python Package for Astronomy
• The Structure of Cold Dark Matter Halos
• Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD
• On the variation of the Initial Mass Function
• The Gaia mission
• PARSEC: stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• Gaia Data Release 2: The astrometric solution
• galpy: A Python Library for Galactic Dynamics
• Small-Scale Challenges to the $\Lambda$CDM Paradigm
• SEGUE: A Spectroscopic Survey of 240,000 stars with g=14-20
• The mass distribution and gravitational potential of the Milky Way
• The Pan-STARRS1 Photometric System
• The Field of Streams: Sagittarius and its Siblings
• 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 Pan-STARRS1 Database and Data Products
• Star counts in the Galaxy. Simulating from very deep to very shallow photometric surveys with the TRILEGAL code
• Gaia Data Release 2: Kinematics of globular clusters and dwarf galaxies around the Milky Way
• The Faintest Dwarf Galaxies
• The Sloan Digital Sky Survey Quasar Catalog: Fourteenth Data Release
• A Faint New Milky Way Satellite in Bootes
• A $Gaia$ Data Release 2 catalogue of white dwarfs and a comparison with SDSS
• Identification of A-colored Stars and Structure in the Halo of the Milky Way from SDSS Commissioning Data
• A Keck/DEIMOS spectroscopic survey of faint Galactic satellites: searching for the least massive dwarf galaxies
• The Pristine survey I: Mining the Galaxy for the most metal-poor stars
• A Complete N-body Model of the Old Open Cluster M67
• A Pair of Bootes: A New Milky Way Satellite
• On a new theoretical framework for RR Lyrae stars I: the metallicity dependence
• Stellar Populations in the Large Magellanic Cloud from 2MASS
• Pre-reionization Fossils, Ultra-faint Dwarfs and the Missing Galactic Satellite Problem
• Milky Way Satellite Census. II. Galaxy--Halo Connection Constraints Including the Impact of the Large Magellanic Cloud
• Accurate Stellar Kinematics at Faint Magnitudes: application to the Bootes~I dwarf spheroidal galaxy
• A MegaCam Survey of Outer Halo Satellites. III. Photometric and Structural Parameters
• The tidal stripping of satellites
• Chemical Enrichment in the Faintest Galaxies: the Carbon and Iron Abundance Spreads in the Boötes I Dwarf Spheroidal Galaxy and the Segue 1 System
• Quantifying Kinematic Substructure in the Milky Way's Stellar Halo
• Blue horizontal branch stars in the Sloan Digital Sky Survey: I. Sample selection and structure in the Galactic halo
• Exploring Halo Substructure with Giant Stars: The Dynamics and Metallicity of the Dwarf Spheroidal in Bootes
• An image of the dust sublimation region in the nucleus of NGC 1068
• Generation of mock tidal streams
• Direct N-Body Modeling of the Old Open Cluster NGC 188: A Detailed Comparison of Theoretical and Observed Binary Star and Blue Straggler Populations
• Variable stars in the newly discovered Milky Way satellite in Bootes
• The Halo's Ancient Metal-Rich Progenitor Revealed with BHB Stars
• Revised and new proper motions for confirmed and candidate Milky Way dwarf galaxies
• An Extremely Carbon-rich, Extremely Metal-poor Star in the Segue 1 System
• Gaia EDR3 proper motions of Milky Way dwarfs I: 3D Motions and Orbits
• An extended halo around an ancient dwarf galaxy
• The Stellar Populations and Structural Properties of Ultra Faint Dwarf Galaxies, Canes Venatici I, Bootes I, Canes Venatici II, and Leo IV
• The abundance spread in the Bootes I dwarf spheroidal galaxy
• EDGE: The origin of scatter in ultra-faint dwarf stellar masses and surface brightnesses
• The chemical evolution of the Bootes I ultra-faint dwarf galaxy
• RR Lyrae Stars in the Bootes dSph
• Bootes II ReBooted: An MMT/MegaCam Study of An Ultra-Faint Milky Way Satellite
• Formation of an extended stellar halo around an ultra-faint dwarf galaxy following one of the earliest mergers from galactic building blocks
• Ecology of Blue Straggler Stars
• VLT Spectroscopy of Ultra-Faint Dwarf Galaxies. 1. Boötes I, Leo IV, Leo V
• Identifying Blue Horizontal Branch Stars Using the z Filter
• Pan-STARRS1: Galaxy Clustering in the Small Area Survey 2
• Hubble Space Telescope proper motion (HSTPROMO) catalogs of Galactic globular clusters. IV. Kinematic profiles and average masses of blue straggler stars
• Gaia RR Lyrae Stars in Nearby Ultra-Faint Dwarf Satellite Galaxies
• Internal rotation of Milky Way dwarf spheroidal satellites with $Gaia$ Early Data Release 3
• Modelling the dynamical evolution of the Bootes dwarf spheroidal galaxy
• A Megacam Survey of Outer Halo Satellites. II. Blue Stragglers in the Lowest Stellar Density Systems
• Galactic Globular and Open Cluster Fiducial Sequences in the Pan-STARRS1 Photometric System
• 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
• Extended stellar substructure surrounding the Boötes I dwarf spheroidal galaxy
• A new calibration for the Blue Horizontal Branch
• Photometric identification of blue horizontal branch stars
• Discovery of long-period variable stars in the very-metal-poor globular cluster M15
• Globular Cluster Intrinsic Iron Abundance Spreads: I. Catalog

Cited by in corpus (9)

• Proper Motions, Orbits, and Tidal Influences of Milky Way Dwarf Spheroidal Galaxies
• Streams on FIRE: Populations of Detectable Stellar Streams in the Milky Way and FIRE
• The Pristine Dwarf-Galaxy survey -- IV. Probing the outskirts of the dwarf galaxy Boötes I
• Detailed chemical abundances of stars in the outskirts of the Tucana II ultra-faint dwarf galaxy
• Stars on the edge: Galactic tides and the outskirts of the Sculptor dwarf spheroidal
• The Pristine Inner Galaxy Survey (PIGS) X. Probing the early chemical evolution of the Sagittarius dwarf galaxy with carbon abundances
• Faint Stars in a Faint Galaxy: II. The Low Mass Stellar Initial Mass Function of the Boötes I Ultrafaint Dwarf Spheroidal Galaxy
• Auriga Streams II: orbital properties of tidally disrupting satellites of Milky Way-mass galaxies
• Willman 1 Revisited: The Kinematics, Chemistry, and Orbital Properties of a Potentially-Disrupting Dwarf Galaxy