Polytropic dark haloes 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 haloes. We fit published data for 14 such galaxies using a spherical, self‐gravitating model with two components: (i) a Sérsic stellar profile fixed according to photometric parameters, and (ii) 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 (Fd) which is proportional to the dark heat capacity. By default, we assume a cosmic ratio of baryonic and dark mass. Non‐Sérsic kinematic ideosyncrasies and possible non‐sphericity thwart fitting in some cases. In all 14 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 Fd values from six to eight. This range complements the recently inferred limit of 7 < Fd < 10, 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 Fd; whereas a loss of baryons would favour higher Fd.

Investigation of dark matter and modified Newtonian dynamics in early-type galaxies through globular cluster systems

“…In the fits below, the values of n * = 4.0 and R (fit) e = 26.6 arcsec are used (Saxton & Ferreras 2010; see also Coccato et al 2009). The Newtonian fits of NGC 1400 are presented in Fig.…”

On extended sign-changeable interactions in the dark sector

“…In this sense, we call lukewarm or generically, warm matter, (baryonic or dark), to that has a lightly positive EoS (0 < ω t < 1/3), reserving the expression "cold matter" for the case of EoS strictly zero. The issue of the dark matter component with a small but non zero pressure was studied in [80][81][82][83][84] in the context of modeling galaxy halos. Also in [85][86][87][88][89][90], WDM particles were invoked as possible solutions to both, the over prediction of satellite galaxies, by almost an order of magnitude larger than the number of satellites that have been observed in Milky-Way sized galaxies and as a mechanism to smooth out the cusped density profiles predicted by CDM simulations.…”

Dark halo microphysics and massive black hole scaling relations in galaxies

“…In galaxy clusters, Saxton & Wu (2008 found that the continuity requirements of gas inflows impose lower limits on m•, however inserting a central galaxy's stellar profile did not alter these constraints greatly. An isolated elliptical galaxy's stellar spheroid compresses the dark core slightly (Saxton & Ferreras 2010;Saxton 2013). Nonetheless DM always dominates in the outer halo.…”

“…More microphysics may be needed. The core sizes can be set by the effective thermal properties of DM in equilibrium (Nunez et al 2006;Saxton & Ferreras 2010;Saxton 2013), or temporarily by heat conduction (Kochanek & White 2000;Davé et al 2001;Ahn & Shapiro 2005;Rocha et al 2013). Alternatively, one may invoke stellar and/or SMBH feedback (see e.g.…”

“…Scaling relations among disc galaxies imply high F (Nunez et al 2006;Zavala et al 2006). From the kinematics of elliptical galaxies, the inference is 7 F 9 (Saxton & Ferreras 2010). Models of galaxy clusters comprising DM and cooling gas inflows predict realistic core sizes and enable realistic m• if 7 F < 10 ( Saxton & Wu 2008.…”