Do the Low PN Velocity Dispersions Around Elliptical Galaxies Imply That These Lack Dark Matter?

2005 ◽  
Author(s):  
Gary A. Mamon
Keyword(s):  
Dark Matter ◽  
Elliptical Galaxies ◽  
Pn Velocity ◽  
Velocity Dispersions

scholarly journals The outer haloes of massive, elliptical galaxies

2009 ◽  
Vol 5 (H15) ◽  
pp. 92-92
Author(s):  
Payel Das ◽  
Ortwin Gerhard ◽  
Flavio de Lorenzi ◽  
Emily McNeil ◽  
Eugene Churazov ◽  
...  
Keyword(s):  
Dark Matter ◽  
Parametric Method ◽  
Elliptical Galaxies ◽  
Matter Content ◽  
Likelihood Method ◽  
Orbital Structure ◽  
Dynamical Models ◽  
X Ray ◽  
Mass Distributions ◽  
Velocity Dispersions

The outer haloes of massive elliptical galaxies are dark-matter dominated regions where stellar orbits have longer dynamical timescales than the central regions and therefore better preserve their formation history. Dynamical models out to large radii suffer from a degeneracy between mass and orbital structure, as the outer kinematics are unable to resolve higher moments of the line-of-sight velocity distribution. We mitigate this degeneracy for a sample of quiescent, massive, nearby ellipticals by determining their mass distributions independently using a non-parametric method on X-ray observations of the surrounding hot interstellar medium. We then create dynamical models using photometric and kinematic constraints consisting of integral-eld, long-slit and planetary nebulae (PNe) data extending to ~50 kpc. The rst two galaxies of our sample, NGC 5846 and NGC 1399, were found to have very shallow pro jected light distributions with a power law index of ~1.5 and a dark matter content of 70–80% at 50 kpc. Spherical Jeans models of the data show that, in the outer haloes of both galaxies, the pro jected velocity dispersions are almost inde- pendent of the anisotropy and that the PNe prefer the lower end of the range of mass distributions consistent with the X-ray data. Using the N-body code NMAGIC, we cre- ated axisymmetric models of NGC 5846 using the individual PNe radial velocities in a likelihood method and found them to be more constraining than the binned velocity dispersions. Characterising the orbital structure in terms of spherically averaged proles of the velocity dispersions we nd σψ > σr > σθ.

Dark matter in elliptical galaxies

1995 ◽  
Author(s):  
Francesco Bertola ◽  
Alessandro Pizzella
Keyword(s):  
Dark Matter ◽  
Elliptical Galaxies

scholarly journals Mass Distribution of the E0 Galaxy NGC 6703 from Absorption Line Profile Kinematics

1999 ◽  
Vol 186 ◽  
pp. 189-190
Author(s):  
O.E. Gerhard ◽  
G. Jeske ◽  
R.P. Saglia ◽  
Ralf Bender
Keyword(s):  
Dark Matter ◽  
Absorption Line ◽  
Mass Distribution ◽  
Line Profile ◽  
Elliptical Galaxies ◽  
Velocity Profiles ◽  
Matter Content ◽  
Orbit Structure ◽  
Extensive Analysis ◽  
Preliminary Account

Absorption line velocity profiles (vps) contain important information on the anisotropy and mass distribution of elliptical galaxies (e.g., Gerhard 1993, Merritt 1993). Here we briefly present results of an extensive analysis of the E0 galaxy NGC 6703 (Gerhard et al. 1997). This work is part of an observational and theoretical program aimed at understanding the orbit structure and dark matter content of ellipticals at intermediate radii (a preliminary account is given in Saglia et al. 1997).

Evidence against baryonic dark matter in elliptical galaxies

1989 ◽  
Vol 346 ◽  
pp. 648 ◽  
Author(s):  
Dennis J. Hegyi ◽  
Keith A. Olive
Keyword(s):  
Dark Matter ◽  
Elliptical Galaxies ◽  
Baryonic Dark Matter

Dark Matter Halos in Elliptical Galaxies

1993 ◽  
Vol 416 ◽  
pp. L45 ◽  
Author(s):  
Francesco Bertola ◽  
Alessandro Pizzella ◽  
Massimo Persic ◽  
Paolo Salucci
Keyword(s):  
Dark Matter ◽  
Elliptical Galaxies ◽  
Dark Matter Halos

scholarly journals A Model for the Sequence of Elliptical Galaxies

1987 ◽  
Vol 117 ◽  
pp. 367-367
Author(s):  
Rosemary F. G. Wyse ◽  
Bernard J. T. Jones
Keyword(s):  
Dark Matter ◽  
Power Spectrum ◽  
Galaxy Formation ◽  
Cold Dark Matter ◽  
Initial Conditions ◽  
Elliptical Galaxy ◽  
Elliptical Galaxies ◽  
Density Fluctuations ◽  
Analytic Approximation ◽  
Non Linear

We present a simple model for the formation of elliptical galaxies, based on a binary clustering hierarchy of dark matter, the chemical enrichment of the gas at each level being controlled by supernovae. The initial conditions for the non-linear phases of galaxy formation are set by the post-recombination power spectrum of density fluctuations. We investigate two models for this power spectrum - the first is a straightforward power law, |δk|2 ∝ kn, and the second is Peeble's analytic approximation to the emergent spectrum in a universe dominated by cold dark matter. The normalisation is chosen such that on some scale, say M ∼ 1012M⊙, the objects that condense out have properties - radius and velocity dispersion - resembling ‘typical’ galaxies. There is some ambiguity in this due to the poorly determined mass-to-light ratio of a typical elliptical galaxy — we look at two normalisations, σ1D ∼ 350kms−1 and σ1D ∼ 140kms−1. The choice determines which of Compton cooling or hydrogen cooling is more important during the galaxy formation period. The non-linear behaviour of the perturbations is treated by the homogeneous sphere approximation.

scholarly journals The Tilt of the Fundamental Plane of Elliptical Galaxies: Dynamical and Structural Effects

1996 ◽  
Vol 171 ◽  
pp. 403-403
Author(s):  
B. Lanzoni ◽  
L. Ciotti ◽  
A. Renzini
Keyword(s):  
Dark Matter ◽  
Velocity Dispersion ◽  
Elliptical Galaxies ◽  
Stellar Mass ◽  
Fine Tuning ◽  
Structural Effects ◽  
Fundamental Plane ◽  
Systematic Trend ◽  
Radial Anisotropy ◽  
Light Profiles

We explore several structural and dynamical effects on the projected velocity dispersion as possible causes of the fundamental plane (FP) tilt of elliptical galaxies (Ciotti, Lanzoni & Renzini, 1995). Specifically, we determine the size of the systematic trend along the FP in the orbital radial anisotropy, in the dark matter (DM) content and distribution relative to the bright matter, and in the shape of the light profile that would be needed to produce the tilt, under the assumption of a constant stellar mass to light ratio. Spherical, non rotating, two-components models are constructed, where the light profiles resemble the R1/4 law. For these we can exclude orbital anisotropy as the origin of the tilt, while a systematic increase in the DM content and/or concentration may formally produce it. Also a suitable variation of the light profile can produce the desired effect, and there may be some observational hints supporting this possibility. However, fine tuning is always required in order to reproduce the tilt, while preserving the tightness of the galaxies distribution about the FP.

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