Influence of a dark halo on the stability of elliptical galaxies

1991 ◽  
Vol 382 ◽  
pp. 466 ◽  
Author(s):  
M. Stiavelli ◽  
L. S. Sparke
Keyword(s):  
Elliptical Galaxies ◽  
Dark Halo ◽  
The Stability

scholarly journals The Dark Halo – Spheroid Conspiracy

2012 ◽  
Vol 8 (S295) ◽  
pp. 208-208
Author(s):  
Rhea-Silvia Remus ◽  
Andreas Burkert ◽  
Klaus Dolag ◽  
Peter H. Johansson ◽  
Thorsten Naab ◽  
...  
Keyword(s):  
Elliptical Galaxies ◽  
Total Density ◽  
Dark Halo ◽  
Coma Cluster ◽  
Density Profiles ◽  
Stellar Component ◽  
Strong Lensing ◽  
The Galaxy ◽  
Good Agreement

AbstractObservational results from strong lensing and dynamical modeling indicate that the total density profiles of early-type galaxies are close to isothermal, i.e. ρtot ∝ rγ with γ ≈ −2. To understand the origin of this universal slope we study a set of simulated spheroids formed in cosmological hydrodynamical zoom-in simulations (see Oser et al. 2010 for more details). We find that the total stellar plus dark matter density profiles of all our simulations on average can be described by a power law with a slope of γ ≈ −2.1, with a tendency towards steeper slopes for more compact, lower mass ellipticals, while the total intrinsic velocity dispersion is flat for all simulations, independent of the values of γ. Our results are in good agreement with observations of Coma cluster ellipticals (Thomas et al. 2007) and results from strong lensing (Sonnenfeld et al. 2012). We find that for z ≳ 2 the majority of the stellar build-up occurs through in-situ star formation, i.e. the gas falls to the center of the galaxy and forms stars, causing the galaxy to be more compact and thus the stellar component to be more dominant. As a result, the total density slopes at z ≈ 2 are generally steeper (around γ ≈ −3). Between z = 2 and z = 0 galaxies grow mostly through dry merging, with each merging event shifting the slope more towards γ ≈ −2. We conclude from our simulations that the steepness of the slope of present day galaxies is a signature of the importance of mostly dry mergers in the formation of an elliptical, and suggest that all elliptical galaxies will with time end up in a configuration with a density slope of γ ≈ −2. For a more detailed analysis with a larger sample of simulations see Remus et al. (2013).

Parameters for Dark Halos

1987 ◽  
Vol 117 ◽  
pp. 119-132 ◽  
Author(s):  
K. C. Freeman
Keyword(s):  
Elliptical Galaxies ◽  
Disk Galaxies ◽  
Dark Halo ◽  
Characteristic Scale ◽  
Rotation Curves ◽  
X Ray ◽  
Unique Information ◽  
Best Estimates

What are the characteristic scale lengths and densities for the dark halos of galaxies, and the typical ratios of dark to luminous mass? For elliptical galaxies, the best estimates come from X-ray data which will be discussed in a later session. For spirals, the best estimates come from rotation curves. I will concentrate on the halo parameters for disk galaxies. At the end, there will be a few comments on stellar dynamical data for ellipticals, and on the unique information available for the dark halo of our Galaxy.

scholarly journals Bars in Cusps

1996 ◽  
Vol 171 ◽  
pp. 357-357 ◽  
Author(s):  
Walter Dehnen
Keyword(s):  
Elliptical Galaxies ◽  
Distribution Functions ◽  
List Type ◽  
Type Number ◽  
Initial Model ◽  
Pattern Speed ◽  
Self Similar ◽  
The Stability ◽  
Inside Out ◽  
Insta Bility

In order to investigate the stability properties of galaxy models with central density cusps, TV-body simulations of oblate models with density ρ ∝ m–1 (m+a)–3 where m2=R2+[z/q]2 and distribution functions f(E, Lz) (computed as in Dehnen, 1995) have been performed with the following results. 1.An E7 model with identical amounts of stars of either sense of rotation was stable over 30 tdyn(r=a). This is interesting for the bending instability has been argued to set in at about this flattening and be responsible for the absence of flatter elliptical galaxies (Merritt & Sellwood, 1994).2.Rapidly rotating E≳E5 models quickly form weak bars inside the cusp, which are stronger for the more flattened, faster rotating initial configurations. The bars grow in a self similar fashion from inside out: the pattern speed decreases with increasing bar length and time. This process is initiated at the origin, where, because of finite AT, the actual density no longer follows the power law, and stops when the edge of the cusp is reached. A typical example is given in the figure showing the z-y-coordinates of particles with |z|<0.1a after ≃20tdyn(r=a) for an initially rapidly rotating E7-model. The bar has axis ratios of about 5:3:1, and extends almost to corotation. However, it has no sharp edge, but an inhomogenous density with a cusp steeper than the initial model. No sign of a buckling insta-bility has been observerd.

scholarly journals Evolution of the Coronae in Early-Type Galaxies

1990 ◽  
Vol 115 ◽  
pp. 240-244
Author(s):  
L.P. David ◽  
W. Forman ◽  
C. Jones
Keyword(s):  
Mass Loss ◽  
Numerical Simulations ◽  
Elliptical Galaxies ◽  
Compact Groups ◽  
Type I ◽  
Dark Halo ◽  
Early Type ◽  
X Ray ◽  
Galactic Winds ◽  
The Galaxy

AbstractWe present numerical simulations of the gaseous coronae in elliptical galaxies. These models consist of a modified King profile for the luminous portion of the galaxy and an isothermal dark halo. We include evolving stellar mass loss from planetary nebulae, and type I and II supernovae. Our models show that elliptical galaxies are likely to produce strong galactic winds at early times with x-ray luminosities of 1042 — 1044 ergs s-1 and temperatures of 10 keV. Galaxies can lose approximately 10-30% of their initial luminous mass in the wind which has an oxygen-to-iron ratio twice the solar value. Since elliptical galaxies are a principle component of rich clusters and compact groups this early wind phase affects the metallicity and temperature of the intracluster medium.

scholarly journals Elliptical galaxies with rapidly decreasing velocity dispersion profiles: nmagic models and dark halo parameter estimates for NGC 4494

2013 ◽  
Vol 431 (4) ◽  
pp. 3570-3588 ◽  
Author(s):  
Lucia Morganti ◽  
Ortwin Gerhard ◽  
Lodovico Coccato ◽  
Inma Martinez-Valpuesta ◽  
Magda Arnaboldi
Keyword(s):  
Velocity Dispersion ◽  
Elliptical Galaxies ◽  
Parameter Estimates ◽  
Dark Halo

The shapes of simulated dark matter halos

2004 ◽  
Vol 220 ◽  
pp. 421-429 ◽  
Author(s):  
Volker Springel ◽  
Simon D. M. White ◽  
Lars Hernquist
Keyword(s):  
Dark Matter ◽  
Major Axis ◽  
Elliptical Galaxies ◽  
Radiative Cooling ◽  
Dark Halo ◽  
Dark Matter Halos ◽  
Robust Method ◽  
Shape Distribution ◽  
Measurement Uncertainties ◽  
Hydrodynamical Simulations

Dark matter halos formed in CDM simulations are known to have triaxial shapes, with substantial distortions from spherical symmetry. However, conflicting claims have been made with respect to radial variations of halo shape, or trends with mass. We propose a new, more robust method to determine halo shapes based on the gravitational potential, thereby avoiding measurement uncertainties that may be the cause of these discrepancies. We find a strong preference towards prolate halo shapes, with mean minor-to-major axis-ratios close to ~ 0.5. Spherical halos are generally very rare, but there is a trend for smaller mass systems to be less elongated. We also compare dark halo shapes found in hydrodynamical simulations that include radiative cooling, star formation, and feedback processes, with those measured in equivalent collisionless simulations. Dissipation makes dark halos substantially rounder at small radii, to the extent that their shape distribution matches that of elliptical galaxies.

scholarly journals The Dark Halo – Spheroid Conspiracy Reloaded: Evolution with Redshift

2014 ◽  
Vol 10 (S311) ◽  
pp. 116-119 ◽  
Author(s):  
Rhea-Silvia Remus ◽  
Klaus Dolag ◽  
Andreas Burkert
Keyword(s):  
Power Law ◽  
Elliptical Galaxies ◽  
Total Density ◽  
Dark Halo ◽  
Density Profiles ◽  
Opposite Trend ◽  
Stellar Component ◽  
Strong Lensing ◽  
Single Power ◽  
Spheroidal Galaxies

AbstractThe total density profiles of elliptical galaxies can be fit by a single power law, i.e., ρtot ∝ rγ with γ ≈ −2. While strong lensing observations show a tendency for the slopes to become flatter with increasing redshift, simulations indicate an opposite trend. To understand this discrepancy, we study a set of simulated spheroids formed within the cosmological framework. From our simulations we find that the steepness of the total density slope correlates with the compactness of the stellar component within the half-mass radius, and that spheroidal galaxies tend to be more compact at high redshifts than their present-day counterparts. While both these results are in agreement with observations, the observed trend of the total density slope with redshift remains in contradiction to the results from simulations.

scholarly journals THE DARK HALO—SPHEROID CONSPIRACY AND THE ORIGIN OF ELLIPTICAL GALAXIES

2013 ◽  
Vol 766 (2) ◽  
pp. 71 ◽  
Author(s):  
Rhea-Silvia Remus ◽  
Andreas Burkert ◽  
Klaus Dolag ◽  
Peter H. Johansson ◽  
Thorsten Naab ◽  
...  
Keyword(s):  
Elliptical Galaxies ◽  
Dark Halo

scholarly journals The Stability of Axisymmetric Galaxy Models with Anisotropic Dispersions

1983 ◽  
Vol 100 ◽  
pp. 285-286
Author(s):  
Tim de Zeeuw ◽  
Marijn Franx ◽  
Jacques Meys ◽  
Karel Brink ◽  
Harm Habing
Keyword(s):  
Spiral Galaxies ◽  
Theoretical Models ◽  
Elliptical Galaxies ◽  
Small Class ◽  
Integrals Of Motion ◽  
Equilibrium Configurations ◽  
Velocity Dispersions ◽  
The Stability

The possible equilibrium configurations for elliptical galaxies and the bulges of spiral galaxies are no longer thought to be confined to the small class of axisymmetric systems with isotropic velocity dispersions. Many of these systems are not supported by rotation but instead by anisotropic velocity dispersions which are maintained by nonclassical integrals of motion (e.g., Binney 1978), and may be triaxial. Few theoretical models for such systems exist (Schwarzschild 1981). Here we discuss some axisymmetric models that we have constructed by means of Schwarzschild's (1979) selfconsistent method, and in particular their stability.

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