The Space Motion of Leo I: Hubble Space Telescope Proper Motion and Implied Orbit

Abstract

We present the first absolute proper motion measurement of Leo I, based on two epochs of HST ACS/WFC images separated by ~5 years. The average shift of Leo I stars with respect to ~100 background galaxies implies a proper motion of (mu_W, mu_N) = (0.1140 +/- 0.0295, -0.1256 +/- 0.0293) mas/yr. The implied Galactocentric velocity vector, corrected for the reflex motion of the Sun, has radial and tangential components V_rad = 167.9 +/- 2.8 km/s and V_tan = 101.0 +/- 34.4 km/s, respectively. We study the detailed orbital history of Leo I by solving its equations of motion backward in time for a range of plausible mass models for the Milky Way and its surrounding galaxies. Leo I entered the Milky Way virial radius 2.33 +/- 0.21 Gyr ago, most likely on its first infall. It had a pericentric approach 1.05 +/- 0.09 Gyr ago at a Galactocentric distance of 91 +/- 36 kpc. We associate these time scales with characteristic time scales in Leo I's star formation history, which shows an enhanced star formation activity ~2 Gyr ago and quenching ~1 Gyr ago. There is no indication from our calculations that other galaxies have significantly influenced Leo I's orbit, although there is a small probability that it may have interacted with either Ursa Minor or Leo II within the last ~1 Gyr. For most plausible Milky Way masses, the observed velocity implies that Leo I is bound to the Milky Way. However, it may not be appropriate to include it in models of the Milky Way satellite population that assume dynamical equilibrium, given its recent infall. Solution of the complete (non-radial) timing equations for the Leo I orbit implies a Milky Way mass M_MW,vir = 3.15 (-1.36, +1.58) x 10^12 Msun, with the large uncertainty dominated by cosmic scatter. In a companion paper, we compare the new observations to the properties of Leo I subhalo analogs extracted from cosmological simulations.

arXiv comment21 pages, 14 figures, 4 tables; Accepted for publication in the Astrophysical Journal

References in corpus (70)

• A Universal Density Profile from Hierarchical Clustering
• Final Results from the Hubble Space Telescope Key Project to Measure the Hubble Constant
• Local Kinematics and the Local Standard of Rest
• A 2MASS All-Sky View of the Sagittarius Dwarf Galaxy: I. Morphology of the Sagittarius Core and Tidal Arms
• Local stellar kinematics from Hipparcos data
• Halos and galaxies in the standard cosmological model: results from the Bolshoi simulation
• Response of dark matter halos to condensation of baryons: cosmological simulations and improved adiabatic contraction model
• Mass models of the Milky Way
• The Milky Way's bright satellites as an apparent failure of LCDM
• Accurate masses for dispersion-supported galaxies
• The Merger Rates and Mass Assembly Histories of Dark Matter Haloes in the Two Millennium Simulations
• New Understanding of Large Magellanic Cloud Structure, Dynamics and Orbit from Carbon Star Kinematics
• Are the Magellanic Clouds on their First Passage about the Milky Way?
• Numerical Methods of Star Formation History Measurement and Applications to Seven Dwarf Spheroidals
• Third-Epoch Magellanic Cloud Proper Motions I: HST/WFC3 data and Orbit Implications
• HI in Local Group Dwarf Galaxies and Stripping by the Galactic Halo
• The Milky Way's circular velocity curve between 4 and 14 kpc from APOGEE data
• The Present and Future Mass of the Milky Way Halo
• Tip of the Red Giant Branch Distances. II. Zero-Point Calibration
• The Role of Dwarf Galaxy Interactions in Shaping the Magellanic System and Implications for Magellanic Irregulars
• The Masses of the Milky Way and Andromeda galaxies
• The Proper Motion of the Large Magellanic Cloud using HST
• Stellar Velocities in the Carina, Fornax, Sculptor and Sextans dSph Galaxies: Data from the Magellan/MMFS Survey
• Is the SMC Bound to the LMC? The HST Proper Motion of the SMC
• The M31 Velocity Vector. II. Radial Orbit Towards the Milky Way and Implied Local Group Mass
• Four New Stellar Debris Streams in the Galactic Halo
• Masses for the Local Group and the Milky Way
• Internal Kinematics of the Fornax Dwarf Spheroidal Galaxy
• An Empirical Pixel-Based Correction for Imperfect CTE. I. HST's Advanced Camera for Surveys
• The Velocity Dispersion Profile of the Remote Dwarf Spheroidal Galaxy Leo I: A Tidal Hit and Run?
• Deviations from the Local Hubble Flow. I. The Tip of the Red Giant Branch as a Distance Indicator
• The Star Formation History of the Local Group dwarf galaxy Leo I
• The Space Motion of Leo I: The Mass of the Milky Way's Dark Matter Halo
• The Mass of the Milky Way Galaxy
• Small Dwarf Galaxies Within Larger Dwarfs: Why Some Are Luminous While Most Go Dark
• The Solar Motion Relative to the Local Group
• Kinematically Cold Populations at Large Radii in the Draco and Ursa Minor Dwarf Spheroidals
• On the Orbits of Infalling Satellite Halos
• Multi-Element Abundance Measurements from Medium-Resolution Spectra. IV. Alpha Element Distributions in Milky Way Dwarf Satellite Galaxies
• Cosmic Ménage à Trois: The Origin of Satellite Galaxies On Extreme Orbits
• The Draco and Ursa Minor dwarf spheroidals. A comparative study
• The Star Formation History and the spatial distribution of stellar populations in the Ursa Minor Dwarf Spheroidal Galaxy
• Exploring Halo Substructure with Giant Stars X. Extended Dark Matter or Tidal Disruption?: The Case for the Leo I Dwarf Spheroidal Galaxy
• Exploring Halo Substructure with Giant Stars IV: The Extended Structure of the Ursa Minor Dwarf Spheroidal
• Stellar kinematics in the remote Leo II dwarf spheroidal galaxy -- Another brick in the wall
• The M31 Velocity Vector. I. Hubble Space Telescope Proper Motion Measurements
• Infall Times for Milky Way Satellites From Their Present-Day Kinematics
• M31 Transverse Velocity and Local Group Mass from Satellite Kinematics
• Mismatch and Misalignment: Dark Haloes and Satellites of Disc Galaxies
• The M31 Velocity Vector. III. Future Milky Way-M31-M33 Orbital Evolution, Merging, and Fate of the Sun
• Proper Motions of Dwarf Spheroidal Galaxies from Hubble Space Telescope Imaging. IV: Measurement for Sculptor
• Proper Motions of Dwarf Spheroidal Galaxies from Hubble Space Telescope Imaging. V: Final Measurement for Fornax
• The Araucaria Project. The Distance to the Sculptor dwarf spheroidal galaxy from infrared photometry of RR Lyrae stars
• Did the Milky Way dwarf satellites enter the halo as a group?
• Systemic Proper Motions of Milky Way Satellites from Stellar Redshifts: the Carina, Fornax, Sculptor and Sextans Dwarf Spheroidals
• Proper Motions of Dwarf Spheroidal Galaxies from Hubble Space Telescope Imaging. III: Measurement for Ursa Minor
• The Red Giant Branch Tip and Bump of the Leo II dwarf spheroidal galaxy
• Clues to the "Magellanic Galaxy" from Cosmological Simulations
• The Spatial Distribution of Galactic Satellites in the LCDM Cosmology
• The distance to the Fornax Dwarf Spheroidal Galaxy
• The distance to the Leo I dwarf spheroidal galaxy from the Red Giant Branch Tip
• The Araucaria Project. Infrared TRGB distances to the Carina and Fornax dwarf spheroidal galaxies
• The Internal Kinematics of the Leo I Dwarf Spheroidal Galaxy: Dark Matter at the Fringe of the Milky Way
• The evolved stars of Leo II dSph galaxy from near-infrared UKIRT/WFCAM observations
• Near-infrared observations of the Fornax dwarf galaxy. I. The red giant branch
• Stellar populations in the dwarf spheroidal galaxy Leo I
• A first measurement of the Proper Motion of the Leo II dwarf spheroidal galaxy
• The shapes of Milky Way satellites: looking for signatures of tidal stirring
• The distance to the Fornax dwarf galaxy using red clump stars, and the discrepancy between red clump and tip of the red giant branch distances
• A near-infrared study of AGB and red giant stars in the Leo I dSph galaxy

Cited by in corpus (99)

• Gaia Data Release 2: Kinematics of globular clusters and dwarf galaxies around the Milky Way
• The RAVE survey: the Galactic escape speed and the mass of the Milky Way
• Third-Epoch Magellanic Cloud Proper Motions II: The Large Magellanic Cloud Rotation Field in Three Dimensions
• Gaia DR2 Proper Motions of Dwarf Galaxies within 420 kpc: Orbits, Milky Way Mass, Tidal Influences, Planar Alignments, and Group Infall
• "Skinny Milky Way, Please", says Sagittarius
• The Space Motion of Leo I: The Mass of the Milky Way's Dark Matter Halo
• Can Feedback Solve the Too Big to Fail Problem?
• The Star Formation Histories of Local Group Dwarf Galaxies II. Searching For Signatures of Reionization
• The rotationally stabilized VPOS and predicted proper motions of the Milky Way satellite galaxies
• The mass of the Milky Way from satellite dynamics
• A Magellanic Origin of the DES Dwarfs
• Gaia Proper Motions and Orbits of the Ultra-Faint Milky Way Satellites
• Gaia early DR3 systemic motions of Local Group dwarf galaxies and orbital properties with a massive Large Magellanic Cloud
• The ACS LCID Project: On the origin of dwarf galaxy types: a manifestation of the halo assembly bias?
• The Dearth of Neutral Hydrogen in Galactic Dwarf Spheroidal Galaxies
• The Missing Satellites of the Magellanic Clouds? Gaia Proper Motions of the Recently Discovered Ultra-Faint Galaxies
• Taking Care of Business in a Flash: Constraining the Timescale for Low-Mass Satellite Quenching with ELVIS
• The mass of our Milky Way
• Rapid Environmental Quenching of Satellite Dwarf Galaxies in the Local Group
• Proper Motions, Orbits, and Tidal Influences of Milky Way Dwarf Spheroidal Galaxies
• The Caterpillar Project: A Large Suite of Milky Way Sized Halos
• The Milky Way's Disk of Classical Satellite Galaxies in Light of Gaia DR2
• The Star Formation Histories of Local Group Dwarf Galaxies III. Characterizing Quenching in Low-Mass Galaxies
• Under Pressure: Quenching Star Formation in Low-Mass Satellite Galaxies via Stripping
• First Gaia Dynamics of the Andromeda System: DR2 Proper Motions, Orbits, and Rotation of M31 and M33
• The no-spin zone: rotation vs dispersion support in observed and simulated dwarf galaxies
• $S^5$: Probing the Milky Way and Magellanic Clouds potentials with the 6-D map of the Orphan-Chenab stream
• The ISLAndS project II: The Lifetime Star Formation Histories of Six Andromeda dSphs
• Effects of baryon removal on the structure of dwarf spheroidal galaxies
• Absolute HST Proper Motion (HSTPROMO) of Distant Milky Way Globular Clusters: Galactocentric Space Velocities and the Milky Way Mass
• Touching The Void: A Striking Drop in Stellar Halo Density Beyond 50 kpc
• Proper motions of Milky Way Ultra-Faint satellites with $Gaia$ DR2 $\times$ DES DR1
• The Formation of the Local Group Planes of Galaxies
• Reproducing properties of MW dSphs as descendants of DM-free TDGs
• Scaling Relations for Dark Matter Annihilation and Decay Profiles in Dwarf Spheroidal Galaxies
• Balancing mass and momentum in the Local Group
• Equilibrium models of the Milky Way mass are biased high by the LMC
• HST absolute Proper Motions of NGC 6681 (M70) and the Sagittarius Dwarf Spheroidal Galaxy
• Broken into Pieces: ATLAS and Aliqa Uma as One Single Stream
• The Velocity Anisotropy of Distant Milky Way Halo Stars from Hubble Space Telescope Proper Motions
• HST Proper Motions of NGC 147 and NGC 185: Orbital Histories and Test of Dynamically Coherent Andromeda Satellite Plane
• Perseus I and the NGC 3109 association in the context of the Local Group dwarf galaxy structures
• Estimating the Mass of the Milky Way Using the Ensemble of Classical Satellite Galaxies
• Orbits of massive satellite galaxies: II. Bayesian Estimates of the Milky Way and Andromeda masses using high precision astrometry and cosmological simulations
• Space Motions of the Dwarf Spheroidal Galaxies Draco and Sculptor based on HST Proper Motions with ~10-year Time Baseline
• A Gaia-PS1-SDSS (GPS1) Proper Motion Catalog Covering 3/4 of the Sky
• Evolution of galactic planes of satellites in the EAGLE simulation
• Comparing M31 and Milky Way Satellites: The Extended Star Formation Histories of Andromeda II and Andromeda XVI
• A Genetic Approach to the History of the Magellanic Clouds
• The bursty star formation history of the Fornax dwarf spheroidal galaxy revealed with the HST
• Breaking a dark degeneracy: The gamma-ray signature of early matter domination
• With and without spectroscopy: Gaia DR2 proper motions of seven Ultra-Faint Dwarf Galaxies
• The Mass Profile of the Milky Way to the Virial Radius from the Illustris Simulation
• The power of teaming up HST and Gaia: the first proper motion measurement of the distant cluster NGC 2419
• The tangential velocity excess of the Milky Way satellites
• The effect of tides on the Fornax dwarf spheroidal galaxy
• The mass of the Milky Way and M31 using the method of least action
• Estimating the Galactic Mass Profile in the Presence of Incomplete Data
• Proper Motion of the Leo II Dwarf Galaxy Based On Hubble Space Telescope Imaging
• The alignment of SDSS satellites with the VPOS: effects of the survey footprint shape
• The Metal-poor non-Sagittarius (?) Globular Cluster NGC 5053: Orbit and Mg, Al and Si Abundances
• HALO7D II: The Halo Velocity Ellipsoid and Velocity Anisotropy with Distant Main Sequence Stars
• Bootes III is a disrupting dwarf galaxy associated with the Styx stellar stream
• Dissecting the stellar content of Leo I: a dwarf irregular caught in transition
• Internal rotation of Milky Way dwarf spheroidal satellites with $Gaia$ Early Data Release 3
• Dynamical analysis of the dark matter and central black hole mass in the dwarf spheroidal Leo I
• Proper Motion of the Draco Dwarf Galaxy Based On Hubble Space Telescope Imaging
• Hubble Space Telescope Proper Motions along the Sagittarius Stream: I. Observations and Results for Stars in Four Fields
• The VMC survey - XVII. The proper motion of the Small Magellanic Cloud and of the Milky Way globular cluster 47 Tucanae
• On the Co-Orbitation of Satellite Galaxies Along the Great Plane of Andromeda: NGC 147, NGC 185, and Expectations from Cosmological Simulations
• The VMC survey -IX. Pilot study of the proper motion of stellar populations in the LMC from 2MASS and VISTA data
• Systematic uncertainties from halo asphericity in dark matter searches
• The Proper Motion of Pyxis: the first use of Adaptive Optics in tandem with HST on a faint halo object
• Tidal features of classical Milky Way satellites in a $\Lambda$CDM universe
• The Orbit and Origin of the Ultra-faint Dwarf Galaxy Segue 1
• Sizing from the Smallest Scales: The Mass of the Milky Way
• Metallicity Distribution Functions of Four Local Group dwarf galaxies
• Astrometry with the Wide-Field InfraRed Space Telescope
• Mass assembly history and infall time of the Fornax dwarf spheroidal galaxy
• The central black hole in the dwarf spheroidal galaxy Leo I Not supermassive, at most an intermediate-mass candidate
• Is the vast polar structure of dwarf galaxies a serious problem for lambda cold dark matter?
• The VMC survey XXVIII. Improved measurements of the proper motion of the Galactic globular cluster 47 Tucanae
• Faint Stars in a Faint Galaxy: II. The Low Mass Stellar Initial Mass Function of the Boötes I Ultrafaint Dwarf Spheroidal Galaxy
• HubPUG: Proper Motions for Local Group Dwarfs observed with HST utilizing Gaia as a Reference Frame
• The Variety of Solutions for Dynamics in the Local Group
• Cold, old and metal-poor: New stellar substructures in the Milky Way's dwarf spheroidals
• A Hyperactive FRB Pinpointed in an SMC-Like Satellite Host Galaxy
• Extreme Tidal Stripping May Explain the Overmassive Black Hole in Leo I: a Proof of Concept
• A New Proper Motion Determination of Leo I
• Harnessing the Hubble Space Telescope Archives: A Catalogue of 21,926 Interacting Galaxies
• Denuded Dwarfs Demystified: Gas Loss from dSph Progenitors and Implications for the Minimum Mass of Galaxies
• Leo I: the classical dwarf spheroidal galaxy with the highest dark-matter density
• A Simulation Based Inference Approach to the Dynamics of the MW-LMC System -- Validation
• A Primeval Magellanic Stream and Others
• A lower bound on the Milky Way mass from general phase-space distribution function models
• Detection of Chemo-Kinematical Structures in Leo I
• Local Group Proper Motion Dynamics
• Machine Learning the Dark Matter Halo Mass of Milky Way-Like Systems
• Quantifying the Milky Way, LMC and their interaction using all-sky kinematics of outer halo stars