MONDian predictions for Newtonian M/L ratios for ultrafaint dSphs

Abstract

Under Newtonian gravity total masses for dSph galaxies will scale as $M_T\propto R_e{\sigma }^2$, with $R_e$ the effective radius and $\sigma$ their velocity dispersion. When both of the above quantities are available, the resulting masses are compared to observed stellar luminosities to derive Newtonian mass to light ratios, given a physically motivated proportionality constant in the above expression. For local dSphs and the growing sample of ultrafaint such systems, the above results in the largest mass to light ratios of any galactic systems known, with values in the hundreds and even thousands being common. The standard interpretation is for a dominant presence of an as yet undetected dark matter component. If however, reality is closer to a MONDian theory at the extremely low accelerations relevant to such systems, $\sigma$ will scale with { stellar mass} $M_{\ast }^{1/4}$. This yields an expression for the mass to light ratio which will be obtained under Newtonian assumptions of $(M/L{)}_N=120R_e({{\rm Y}}_{\ast }/L{)}^{1/2}$. Here we compare $(M/L{)}_N$ values from this expression to Newtonian inferences for this ratios for the actual $(R_e,\sigma ,L)$ observed values for a sample of recently observed ultrafaint dSphs, obtaining good agreement. Then, for systems where no $\sigma$ values have been reported, we give predictions for the $(M/L{)}_N$ values which under a MONDian scheme are expected once kinematical observations become available. For the recently studied Dragonfly 44 { and Crater II systems}, reported $(M/L{)}_N$ values are also in good agreement with MONDian expectations.

arXiv comment6 pages, 3 figures, accepted for publication in MNRAS

References in corpus (41)

• Dark Matter Substructure in Galactic Halos
• Too big to fail? The puzzling darkness of massive Milky Way subhaloes
• Modified Newtonian Dynamics (MOND): Observational Phenomenology and Relativistic Extensions
• Observational and Theoretical Constraints on Singular Dark Matter Halos
• Modified Newtonian Dynamics as an Alternative to Dark Matter
• Accurate masses for dispersion-supported galaxies
• The Radial Acceleration Relation in Rotationally Supported Galaxies
• 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
• Forty-Seven Milky Way-Sized, Extremely Diffuse Galaxies in the Coma Cluster
• One Law To Rule Them All: The Radial Acceleration Relation of Galaxies
• A High Stellar Velocity Dispersion and ~100 Globular Clusters for the Ultra Diffuse Galaxy Dragonfly 44
• 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
• Big fish, small fish: Two New Ultra-Faint Satellites of the Milky Way
• Families of dynamically hot stellar systems over ten orders of magnitude in mass
• Non-parametric star formation histories for 5 dwarf spheroidal galaxies of the local group
• Kinematics and chemistry of recently discovered Reticulum 2 and Horologium 1 dwarf galaxies
• Spectroscopic Confirmation of the Dwarf Galaxies Hydra II and Pisces II and the Globular Cluster Laevens 1
• Crater 2: An Extremely Cold Dark Matter Halo
• Magellan/M2FS Spectroscopy of Tucana 2 and Grus 1
• At the survey limits: discovery of the Aquarius 2 dwarf galaxy in the VST ATLAS and the SDSS data
• Search for high-mass diphoton resonances in proton-proton collisions at 13 TeV and combination with 8 TeV search
• The episodic Star Formation History of the Carina Dwarf Spheroidal Galaxy
• Triangulum II: Possibly a Very Dense Ultra-Faint Dwarf Galaxy
• Portrait of a Dark Horse: a Photometric and Spectroscopic Study of the Ultra-faint Milky Way Satellite Pegasus III
• MOND Prediction for the Velocity Dispersion of the `Feeble Giant' Crater II
• Is Draco II one of the faintest dwarf galaxies? First study from Keck/DEIMOS spectroscopy
• Linear relation between HI circular velocity and stellar velocity dispersion in early-type galaxies, and slope of the density profiles
• A natural approach to extended Newtonian gravity: tests and predictions across astrophysical scales
• Understanding local Dwarf Spheroidals and their scaling relations under MOdified Newtonian Dynamics
• A census of the expected properties of classical Milky Way dwarfs in Milgromian dynamics
• Understanding the internal dynamics of elliptical galaxies without non-baryonic dark matter
• NGC 2419 does not challenge MOND
• A universal velocity dispersion profile for pressure supported systems: evidence for MONDian gravity across 7 orders of magnitude in mass
• The Potential of the Dwarf Galaxy Triangulum II for Dark Matter Indirect Detection
• The Present and Future of Searching for Dark Matter with LUX and LZ
• Search for dark matter from the first data of the PandaX-II experiment
• The massive elliptical galaxy NGC 4649 from the perspective of extended gravity
• MONDian dynamical modeling of NGC 288 with $\beta \ne 0$
• Isothermal distributions in MONDian gravity as a simple unifying explanation for the ubiquitous $\rho \propto r^{-3}$ density profiles in tenuous stellar halos

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