Dark matter in elliptical galaxies — II. Estimating the mass within the virial radius

By G. Mamon, E. L. L. Iap, París, France., Camk, Warsaw, Poland. 2004

232 citations recorded by the source corpus.

Elliptical galaxies are modelled with a a 4-component model: Sersic stars, �CDM dark matter (DM), a β-model for the hot gas and a central black hole, with the aim of establishing how accurately can one measure the total mass within their virial radii. DM is negligible in the inner regions, which are dominated by stars and the central black hole. This prevents any kinematical estimate (using a Jeans analysis) of the inner slope of the DM density profile. The gas fraction rises, but the baryon fra ction decreases with radius, at least out to 10 effective radii (Re). Even with line-of-sight velocity dispersion (VD) measure- ments at 4 or 5 Re with 20kms 1 accuracy and perfectly known velocity anisotropy, the total mass within the virial radius (rvr200) is uncertain by a factor over 3. The DM distributions found inCDM simulations appear inconsistent with the low VDs measured by Romanowsky et al. (2003) of planetary nebulae between 2 and 5 Re, which typically (but not always) imply very low M/Ls, and a baryon fraction within rv that is greater than the universal value. Re- placing the NFW DM model by the new model of Navarro et al. (2004) decreases slightly the VD at a given radius. So, given the observed VD measured at 5 Re, the inferred M/L within rv is 40% larger than predicted with the NFW model. Folding in the slight (strong) radial anisotropy found inCDM (merger) simulations, which is well modelled (much better than with the Osipkov-Merritt formula) with β(r) = 1/2 r/(r + a), the inferred M/L within rv is 1.6 (2.4) times higher than for the isotropic NFW model. Thus, the DM model and radial anisotropy can partly explain the low PN VDs, but not in full. The logarithmic slope of the VD at radii of 1 to 5 Re, which is insensitive to radius, is another measure of the DM mass within the virial radius, but it is similarly affected by the a priori unknown DM mass profile and stellar velocity anisotropy. Some of the orbital solutions produced by Romanowsky et al. (2003) indicate that NGC 3379 has a dark matter content at least as large as cosmologically predicted, and the lower M/Ls of most of their solutions lead to a baryonic fraction withi n rv that is larger than the universal value. In an appendix, single integral expres sions are derived for the VDs in terms of general radial profiles for the tracer density and to tal mass, for various anisotropic models (general constant anisotropy, radial, Osipkov-Merritt, and the model above).

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/99e41e3390e10901c5b20ce94953924ca3f635a1

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

In Nuclear and High Energy Physics

Citations in the corpus

CLASH-VLT: The mass, velocity-anisotropy, and pseudo-phase-space density profiles of the z = 0.44 galaxy cluster MACS J1206.2-0847 (2013, methodology): “Note that the MAMPOSSt best-fit T β(r) model is identical to the model that has been shown (Mamon & Łokas 2005; Mamon et al. 2010, 2013) to adequately describe theβ(r) of cluster-mass halos extracted from cosmological simulations.”
The ATLAS3D project XV: benchmark for early-type galaxies scaling relations from 260 dynamical models: mass-to-light ratio, dark matter, fundamental plane and mass plane (2012, background): “Given that the SAURON data are typically spatially limited to 1Re, one cannot expect to be able to robustly characterize the shape of the dark halo out to large radii from them (Mamon & Łokas 2005).”
DWARF GALAXY ANNIHILATION AND DECAY EMISSION PROFILES FOR DARK MATTER EXPERIMENTS (2014, unknown): “Equation 11 has the general solution (van der Marel 1994; Mamon & Łokas 2005) ν(r)u2r (r) = 1 f (r) ∫ ∞ r f (s)ν(s) GM(s) s2 ds, (14) where f (r) = 2 f (r1) exp [∫ r r1 βa(s)s−1 ds ] .”
Generalized Curvature-Matter Couplings in Modified Gravity (2014, background): “By assuming that the anisotropy is a constant, the Jeans equation has the solution [163]:”
MAMPOSSt: Modelling Anisotropy and Mass Profiles of Observed Spherical Systems – I. Gaussian 3D velocities (2012, methodology): “The radial squared velocity dispersion profile of equation (9) can be written (van der Marel 1994; Mamon & Łokas 2005) σ2r(r) = 1 K(r) ν(r) ∫ ∞ r K(s) ν(s) GM(s) s2 ds , (A1) whereK(r) is the solution tod lnK/d ln r = 2β(r), i.e.”
Galaxy Masses: A Review (2013, background): “Inclusion of velocity anisotropy, with β = r/2/(r + aβ) (Mamon & Lokas 2005b), where aβ = 2Re as found for ellipticals formed by mergers by Dekel et al. (2005), makes no difference when Rσ → ∞ (as theoretically expected) and decreases c by typically only 4% for finite Rσ.”