Dynamical Histories of the Crater II and Hercules Dwarf Galaxies

Abstract

We investigate the possibility that the dwarf galaxies Crater II and Hercules have previously been tidally stripped by the Milky Way. We present Magellan/IMACS spectra of candidate member stars in both objects. We identify 37 members of Crater II, 25 of which have velocity measurements in the literature, and we classify 3 stars within that subset as possible binaries. We find that including or removing these binary candidates does not change the derived velocity dispersion of Crater II. Excluding the binary candidates, we measure a velocity dispersion of ${\sigma }_{V_{los}}=2.7_{-0.4}^{+0.5}$ \kms, corresponding to $M/L=47_{-13}^{+17}$ M${}_{\odot }/$L${}_{\odot }$. We measure a mean metallicity of [Fe/H] = $-1.95_{-0.05}^{+0.06}$, with a dispersion of $σ_{\mbox{[Fe/H]}} = 0.18^{+0.06}_{-0.08}$. Our velocity dispersion and metallicity measurements agree with previous measurements for Crater II, and confirm that the galaxy resides in a kinematically cold dark matter halo. We also search for spectroscopic members stripped from Hercules in the possible extratidal stellar overdensities surrounding the dwarf. For both galaxies, we calculate proper motions using \textit{Gaia} DR2 astrometry, and use their full 6D phase space information to evaluate the probability that their orbits approach sufficiently close to the Milky Way to experience tidal stripping. Given the available kinematic data, we find a probability of $\sim$40% that Hercules has suffered tidal stripping. The proper motion of Crater II makes it almost certain to be stripped.

arXiv comment19 pages, 11 figures, submitted to ApJ

References in corpus (73)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• emcee: The MCMC Hammer
• Gaia Data Release 2. Summary of the contents and survey properties
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD
• The Gaia mission
• SDSS-III: Massive Spectroscopic Surveys of the Distant Universe, the Milky Way Galaxy, and Extra-Solar Planetary Systems
• Local Kinematics and the Local Standard of Rest
• The VizieR database of Astronomical Catalogues
• galpy: A Python Library for Galactic Dynamics
• Small-Scale Challenges to the $\Lambda$CDM Paradigm
• The mass distribution and gravitational potential of the Milky Way
• A 2MASS All-Sky View of the Sagittarius Dwarf Galaxy: I. Morphology of the Sagittarius Core and Tidal Arms
• A new generation of PARSEC-COLIBRI stellar isochrones including the TP-AGB phase
• The Kinematics of the Ultra-Faint Milky Way Satellites: Solving the Missing Satellite Problem
• Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way Companions
• The DEEP2 Galaxy Redshift Survey: Design, Observations, Data Reduction, and Redshifts
• Accurate masses for dispersion-supported galaxies
• Gaia Data Release 2: Kinematics of globular clusters and dwarf galaxies around the Milky Way
• Reconciling dwarf galaxies with LCDM cosmology: Simulating a realistic population of satellites around a Milky Way-mass galaxy
• Eight New Milky Way Companions Discovered in First-Year Dark Energy Survey Data
• Are the Magellanic Clouds on their First Passage about the Milky Way?
• Beasts of the Southern Wild: Discovery of nine Ultra Faint satellites in the vicinity of the Magellanic Clouds
• Eight Ultra-faint Galaxy Candidates Discovered in Year Two of the Dark Energy Survey
• The Tidal Evolution of Local Group Dwarf Spheroidals
• The Effects of Photoionization on Galaxy Formation - II: Satellites in the Local Group
• Gaia DR2 Proper Motions of Dwarf Galaxies within 420 kpc: Orbits, Milky Way Mass, Tidal Influences, Planar Alignments, and Group Infall
• Sagittarius II, Draco II and Laevens 3: three new Milky Way satellites discovered in the Pan-STARRS 1 3pi Survey
• The feeble giant. Discovery of a large and diffuse Milky Way dwarf galaxy in the constellation of Crater
• Internal Kinematics of the Fornax Dwarf Spheroidal Galaxy
• A MegaCam Survey of Outer Halo Satellites. III. Photometric and Structural Parameters
• The hidden giant: discovery of an enormous Galactic dwarf satellite in Gaia DR2
• The Space Motion of Leo I: The Mass of the Milky Way's Dark Matter Halo
• A kinematic study of the Andromeda dwarf spheroidal system
• The SPLASH Survey: Spectroscopy of 15 M31 Dwarf Spheroidal Satellite Galaxies
• Stellar Kinematics and Metallicities in the Ultra-Faint Dwarf Galaxy Reticulum II
• Farthest Neighbor: The Distant Milky Way Satellite Eridanus II
• Evidence for an Intermediate-Mass Milky Way from Gaia DR2 Halo Globular Cluster Motions
• The PAndAS view of the Andromeda satellite system - II. Detailed properties of 23 M31 dwarf spheroidal galaxies
• Gaia Proper Motions and Orbits of the Ultra-Faint Milky Way Satellites
• The Missing Satellites of the Magellanic Clouds? Gaia Proper Motions of the Recently Discovered Ultra-Faint Galaxies
• Crater 2: An Extremely Cold Dark Matter Halo
• Infall Times for Milky Way Satellites From Their Present-Day Kinematics
• The Near Infrared Ca II Triplet as Metallicity Indicator: II Extension to extremely metal-poor metallicity regimes
• Nearest Neighbor: The Low-Mass Milky Way Satellite Tucana III
• Tidal stripping and the structure of dwarf galaxies in the Local Group
• A Deeper Look at the New Milky Way Satellites: Sagittarius II, Reticulum II, Phoenix II, and Tucana III
• The Star Formation History and Extended Structure of the Hercules Milky Way Satellite
• Proper motions of Milky Way Ultra-Faint satellites with $Gaia$ DR2 $\times$ DES DR1
• The First Tidally Disrupted Ultra-Faint Dwarf Galaxy? - Spectroscopic Analysis of the Tucana III Stream
• A new low mass for the Hercules dSph: the end of a common mass scale for the dwarfs?
• Constraining the distribution of dark matter in dwarf spheroidal galaxies with stellar tidal streams
• Modelling the Tucana III stream - a close passage with the LMC
• The Orbital Ellipticity of Satellite Galaxies and the Mass of the Milky Way
• Fiducial Stellar Population Sequences for the u'g'r'i'z' System
• The Binary Fraction of Stars in Dwarf Galaxies: the Cases of Draco and Ursa Minor
• Stellar Archaeology in the Galactic halo with Ultra-Faint Dwarfs: VII. Hercules
• Tidal disruption of dwarf spheroidal galaxies: the strange case of Crater II
• Estimating the Mass of the Milky Way Using the Ensemble of Classical Satellite Galaxies
• MOND Prediction for the Velocity Dispersion of the `Feeble Giant' Crater II
• Robust velocity dispersion and binary population modeling of the ultra-faint dwarf galaxy Reticulum II
• With and without spectroscopy: Gaia DR2 proper motions of seven Ultra-Faint Dwarf Galaxies
• The Hercules satellite: a stellar stream in the Milky Way halo?
• Upper Limit on the Milky Way Mass from the Orbit of the Sagittarius Dwarf Satellite
• Stellar Substructures around the Hercules Dwarf Spheroidal Galaxy
• Mapping the Tidal Disruption of the Hercules Dwarf: A Wide-Field DECam Imaging Search for RR Lyrae Stars
• Bootes III is a disrupting dwarf galaxy associated with the Styx stellar stream
• Exploding Satellites -- The Tidal Debris of the Ultra-Faint Dwarf Galaxy Hercules
• The stretching of Hercules
• Estimating the Milky Way's Mass via Hierarchical Bayes: A Blind Test on MUGS2 Simulated Galaxies
• RR Lyrae Variable Stars in the Crater II Dwarf Galaxy
• Life and death of a hero - Lessons learned from modeling the dwarf spheroidal Hercules: an incorrect orbit?
• Variable Stars in Local Group Galaxies. IV. RR Lyrae stars in the central regions of the low-density galaxy Crater II

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• Streams on FIRE: Populations of Detectable Stellar Streams in the Milky Way and FIRE
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• Signatures of Tidal Disruption in Ultra-Faint Dwarf Galaxies: A Combined HST, Gaia, and MMT/Hectochelle Study of Leo V
• Self-interacting dark matter interpretation of Crater II
• Testing the parametric model for self-interacting dark matter using matched halos in cosmological simulations
• A DECam View of the Diffuse Dwarf Galaxy Crater II: The Colour-Magnitude Diagram
• A Statistical Detection of Wide Binary Systems in the Ultra-Faint Dwarf Galaxy Reticulum II
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• The Elusive Distance Gradient in the Ultra-Faint Dwarf Galaxy Hercules: A Combined Hubble Space Telescope and Gaia View
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• Understanding the "Feeble Giant" Crater II with tidally stretched Wave Dark Matter
• Exploring the Diversity of Faint Satellites in the M81 Group
• Galactic tides and the Crater II dwarf spheroidal: a challenge to LCDM?
• Structural parameters and possible association of the Ultra-Faint Dwarfs Pegasus III and Pisces II from deep Hubble Space Telescope photometry
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