Polytropic dark halos of elliptical galaxies

Abstract

The kinematics of stars and planetary nebulae in early type galaxies provide vital clues to the enigmatic physics of their dark matter halos. We fit published data for fourteen such galaxies using a spherical, self-gravitating model with two components: (1) a Sersic stellar profile fixed according to photometric parameters, and (2) a polytropic dark matter halo that conforms consistently to the shared gravitational potential. The polytropic equation of state can describe extended theories of dark matter involving self-interaction, non-extensive thermostatistics, or boson condensation (in a classical limit). In such models, the flat-cored mass profiles widely observed in disc galaxies are due to innate dark physics, regardless of any baryonic agitation. One of the natural parameters of this scenario is the number of effective thermal degrees of freedom of dark matter (F_d) which is proportional to the dark heat capacity. By default we assume a cosmic ratio of baryonic and dark mass. Non-Sersic kinematic ideosyncrasies and possible non-sphericity thwart fitting in some cases. In all fourteen galaxies the fit with a polytropic dark halo improves or at least gives similar fits to the velocity dispersion profile, compared to a stars-only model. The good halo fits usually prefer F_d values from six to eight. This range complements the recently inferred limit of 7<F_d<10 (Saxton & Wu), derived from constraints on galaxy cluster core radii and black hole masses. However a degeneracy remains: radial orbital anisotropy or a depleted dark mass fraction could shift our models' preference towards lower F_d; whereas a loss of baryons would favour higher F_d.

17 pages, 10 figures, 2 tables. MNRAS accepted

References in corpus (19)

• Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Likelihoods and Parameters from the WMAP data
• Kinematic properties of early-type galaxy haloes using planetary nebulae
• Dynamical modelling of luminous and dark matter in 17 Coma early-type galaxies
• Erasing Dark Matter Cusps in Cosmological Galactic Halos with Baryons
• High Resolution Optical Velocity Fields of 11 Low Surface Brightness Galaxies
• The PN.S Elliptical Galaxy Survey: the dark matter in NGC 4494
• Stellar velocity profiles and line strengths out to four effective radii in the early-type galaxies NGC 3379 and NGC 821
• Dearth of dark matter or massive dark halo? Mass-shape-anisotropy degeneracies revealed by NMAGIC dynamical models of the elliptical galaxy NGC 3379
• The shape of the dark matter halo in the early-type galaxy NGC 2974
• Dark matter content and internal dynamics of NGC 4697: NMAGIC particle models from slit data and planetary nebulae velocities
• Dynamical Models of Elliptical Galaxies in z=0.5 Clusters: II. Mass-to-Light Ratio Evolution without Fundamental Plane Assumptions
• Testing the nature of S0 galaxies using planetary nebula kinematics in NGC 1023
• Halo density reduction by baryonic settling?
• The early-type galaxies NGC 1407 and NGC 1400 - I: spatially resolved radial kinematics and surface photometry
• Axisymmetric dynamical models for SAURON and OASIS observations of NGC 3377
• Stellar polytropes and Navarro-Frenk-White halo models: comparison with observations
• Radial structure, inflow & central mass of stationary radiative galaxy clusters
• A catalog of planetary nebulae in the elliptical galaxy NGC 4697
• Mapping the distribution of luminous and dark matter in strong lensing galaxies

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• Physically motivated fit to mass surface density profiles observed in galaxies