The fundamental plane of elliptical galaxies with modified Newtonian dynamics

Abstract

The modified Newtonian dynamics (MOND), suggested by Milgrom as an alternative to dark matter, implies that isothermal spheres with a fixed anisotropy parameter should exhibit a near perfect relation between the mass and the fourth power of the velocity dispersion. This is consistent with the observed Faber-Jackson relation for elliptical galaxies-- a luminosity-velocity dispersion relation with large scatter. However, the observable global properties of elliptical galaxies comprise a three parameter family; they lie on a ``fundamental plane'' in a logarithmic space consisting of central velocity dispersion, effective radius, and luminosity. The scatter perpendicular to this plane is significantly less than that about the Faber-Jackson relation. I show here that, in order to match the observed global properties of elliptical galaxies with MOND, models must deviate from being strictly isothermal and isotropic; such objects can be approximated by high-order polytropic spheres with a radial orbit anisotropy in the outer regions. MOND imposes boundary conditions on the inner Newtonian regions which restrict these models to a dynamical fundamental plane which may differ from that implied by the traditional virial theorem. Scatter about this plane is relatively insensitive to the necessary deviations from homology.

9 pages, 6 eps figures, mn style. Shortened and revised version includes more recent data on elliptical galaxies. Accepted for publication in MNRAS

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• Problems for MOND in Clusters and the Ly-alpha Forest
• Dark matters on the scale of galaxies
• BOOMERanG Data Suggest a Purely Baryonic Universe
• The Universal Faber-Jackson Relation
• The distribution and morphologies of Fornax Cluster dwarf galaxies suggest they lack dark matter
• Dissipationless collapses in MOND
• Confrontation of MOND Predictions with WMAP First Year Data
• Forming Galaxies with MOND
• Gravitational lensing in modified Newtonian dynamics
• The MOND Fundamental Plane
• The Faber-Jackson relation and Fundamental Plane from halo abundance matching
• MOND and the lensing Fundamental Plane: No need for dark matter on galaxy scales
• Modified gravity without dark matter
• Remarks on the properties of elliptical galaxies in modified Newtonian dynamics
• MOND and IMF variations in early-type galaxies from $ATLA{S}^{3D}$
• NGC 2419 does not challenge MOND
• Radial-orbit instability in modified Newtonian dynamics
• A Test of MONDian Gravity in $\sim$300 pressure supported elliptical galaxies from the MaNGA survey
• Origin of the fundamental plane of elliptical galaxies in the Coma Cluster without fine-tuning
• Deep-MOND polytropes
• Galaxy Bulges As Tests of CDM vs MOND in Strong Gravity
• Low-surface-brightness spheroidal galaxies as Milgromian isothermal spheres
• Sub-mm gravity: confronting the modified dynamics with higher-dimensional theories