The Challenge to MOND from ultra faint dwarf galaxies

Abstract

Modified Newtonian Dynamics (MOND) at low acceleration has been astonishingly powerful at explaining the flat rotation curve of galaxies and the relation between the baryonic content of the galaxies and their observed circular velocity, known as the Baryonic Tully-Fisher Relationship (BTFR). It is known that MOND fails at explaining the observed velocity dispersion of the ultra-faint dwarf galaxies (UFDs) with the justification that UFDs are more prone to tidal disruption in MOND compared to cold dark matter model. We show that: (i) the ratio of tidal to internal acceleration in UFDs is extremely low, (ii) there is no correlation between the deviation of UFDs from MOND's prediction as a function of tidal susceptibility, and (iii) recent constraints from Gaia proper motion analysis on the orbital parameters of the UFDs exacerbates the challenge to MOND. In particular, Gaia data indicates that Ursa Major I is experiencing a recent infall into the Milky Way's halo, and its inconsistency with MOND at 7-$\sigma$ level can not be attributed to being an early infall satellite. Moreover, the new data from Gaia DR2 shows Willman I to have the least eccentric orbit of all UFDs, and its deviation from MOND at 4-$\sigma$ level can not be attributed to a highly eccentric orbit as previously suggested. Finally, given that Tucana III is the only UFD observed to show tidal features, Reticulum II and Segue I are two other UFDs that potentially challenge MOND as they have comparable galactocentric distances to Tucana III while showing no tidal features. Whether wide binaries have inflated the velocity dispersion of the UFDs remains an open question to be addressed with future multi-epoch observations.

arXiv commentRevised version, accepted for publication at ApJ Letters

References in corpus (51)

• The observed properties of dwarf galaxies in and around the Local Group
• Trigonometric Parallaxes of High Mass Star Forming Regions: the Structure and Kinematics of the Milky Way
• The Kinematics of the Ultra-Faint Milky Way Satellites: Solving the Missing Satellite Problem
• A model for cosmological simulations of galaxy formation physics
• The Baryonic Tully-Fisher Relation
• The Universal Stellar Mass-Stellar Metallicity Relation for Dwarf Galaxies
• Modified Newtonian Dynamics as an Alternative to Dark Matter
• Accurate masses for dispersion-supported galaxies
• Forming Disk Galaxies in Lambda CDM Simulations
• The Impact of cold gas accretion above a mass floor on galaxy scaling relations
• Eight New Milky Way Companions Discovered in First-Year Dark Energy Survey Data
• Emergent Gravity and the Dark Universe
• The Faintest Dwarf Galaxies
• Beasts of the Southern Wild: Discovery of nine Ultra Faint satellites in the vicinity of the Magellanic Clouds
• The Baryonic Tully-Fisher Relation of Galaxies with Extended Rotation Curves and the Stellar Mass of Rotating Galaxies
• Simulations of Galaxy Formation in a Lambda CDM Universe I: Dynamical and Photometric Properties of a Simulated Disk Galaxy
• Hundreds of Milky Way Satellites? Luminosity Bias in the Satellite Luminosity Function
• The Impact of Baryonic Physics on the Structure of Dark Matter Halos: the View from the FIRE Cosmological Simulations
• Milky Way Satellite Census. III. Constraints on Dark Matter Properties from Observations of Milky Way Satellite Galaxies
• A Complete Spectroscopic Survey of the Milky Way Satellite Segue 1: The Darkest Galaxy
• Theory of Dark Matter Superfluidity
• Gaia DR2 Proper Motions of Dwarf Galaxies within 420 kpc: Orbits, Milky Way Mass, Tidal Influences, Planar Alignments, and Group Infall
• Accurate Stellar Kinematics at Faint Magnitudes: application to the Bootes~I dwarf spheroidal galaxy
• Stellar Kinematics and Metallicities in the Ultra-Faint Dwarf Galaxy Reticulum II
• Farthest Neighbor: The Distant Milky Way Satellite Eridanus II
• Gaia Proper Motions and Orbits of the Ultra-Faint Milky Way Satellites
• Segue 2: The Least Massive Galaxy
• Kinematics and chemistry of recently discovered Reticulum 2 and Horologium 1 dwarf galaxies
• Local Group Dwarf Spheroidals: Correlated Deviations from the Baryonic Tully-Fisher Relation
• Crater 2: An Extremely Cold Dark Matter Halo
• Infall Times for Milky Way Satellites From Their Present-Day Kinematics
• Nearest Neighbor: The Low-Mass Milky Way Satellite Tucana III
• Triangulum II: Not Especially Dense After All
• Andromeda Dwarfs in Light of MOND. II. Testing Prior Predictions
• An Alternative to Particle Dark Matter
• A Deeper Look at the New Milky Way Satellites: Sagittarius II, Reticulum II, Phoenix II, and Tucana III
• The low-mass end of the baryonic Tully-Fisher relation
• Ultra-light Dark Matter is Incompatible with the Milky Way's Dwarf Satellites
• Andromeda Dwarfs in Light of MOND
• Fuzzy Dark Matter and Dark Matter Halo Cores
• The First Tidally Disrupted Ultra-Faint Dwarf Galaxy? - Spectroscopic Analysis of the Tucana III Stream
• Narrowing the mass range of Fuzzy Dark Matter with Ultra-faint Dwarfs
• Dynamical friction in modified Newtonian dynamics
• Birds of a Feather? Magellan/IMACS Spectroscopy of the Ultra-Faint Satellites Grus II, Tucana IV, and Tucana V
• The Binary Fraction of Stars in Dwarf Galaxies: the Cases of Draco and Ursa Minor
• MOND Prediction for the Velocity Dispersion of the `Feeble Giant' Crater II
• Chemical Abundance Analysis of Three $\alpha$-Poor, Metal-Poor Stars in the Ultra-Faint Dwarf Galaxy Horologium I
• Deep neutral hydrogen observations of Leo T with the Westerbork Synthesis Radio Telescope
• Resolving the timing problem of the globular clusters orbiting the Fornax dwarf galaxy
• The star formation history of Eridanus II: on the role of SNe feedback in the quenching of ultra-faint dwarf galaxies
• The Tucana dwarf spheroidal galaxy: not such a massive failure after all

Cited by in corpus (7)

• Open star clusters and their asymmetrical tidal tails
• A Statistical Detection of Wide Binary Systems in the Ultra-Faint Dwarf Galaxy Reticulum II
• Dwarf galaxies with central cores in modified Newtonian dynamics (MOND) gravity
• The p-Laplacian as a Framework for Generalizing Newtonian Gravity and MoND
• The Atacama Cosmology Telescope: A Test of the Gravitational Force Law on Cosmological Scales Using the Kinematic Sunyaev-Zeldovich Effect
• Testing QUMOND theory with Galactic globular clusters in a weak external field
• The Baryonic Tully-Fisher Relation in the Local Group and the Equivalent Circular Velocity of Pressure Supported Dwarfs