179 research outputs found
Dynamical models for dusty disk galaxies
Disk galaxies contain a large amount of interstellar dust, which affects the
projection of kinematic quantities. We investigate in detail the effects of
dust extinction on the mean projected velocity and the projected velocity
dispersion. We use our results to construct a general strategy to determine the
dynamical structure of disk galaxies, with the aim to constrain their mass
distribution and dynamical history.Comment: to be published in the proceedings of "Galaxy Disks and Disk
Galaxies", Funes J.G. and Corsini E.M. eds., ASP Conference Serie
Spherical cosmological models: an alternative cosmology
The properties of universes are explored that are entirely in the interior of
black holes. It is argued that these models offer a paradigm that may shed a
new light on old cosmological problems. The topics that are addressed include:
geometry of the universes, evolution, relation to the concordance model, dark
matter, dark energy, mass ejection from black holes, galaxy models with a
central black hole, Mach's principle
Dynamical models of NGC 3115
We present new dynamical models of the S0 galaxy N3115, making use of the
available published photometry and kinematics as well as of two-dimensional
TIGER spectrography. We first examined the kinematics in the central 40 arcsec
in the light of two integral f(E,J) models. Jeans equations were used to
constrain the mass to light ratio, and the central dark mass whose existence
was suggested by previous studies. The even part of the distribution function
was then retrieved via the Hunter & Qian formalism. We thus confirmed that the
velocity and dispersion profiles in the central region could be well fit with a
two-integral model, given the presence of a central dark mass of ~10^9 Msun.
However, no two integral model could fit the h_3 profile around a radius of 25
arcsec where the outer disc dominates the surface brightness distribution.
Three integral analytical models were therefore built using a Quadratic
Programming technique. These models showed that three integral components do
indeed provide a reasonable fit to the kinematics, including the higher
Gauss-Hermite moments. Again, models without a central dark mass failed to
reproduce the observed kinematics in the central arcseconds. This clearly
supports the presence of a nuclear black hole of at least 6.5 10^8 Msun in the
centre of NGC 3115. These models were finally used to estimate the importance
of the dark matter in the outer part of NGC 3115, suggested by the flat stellar
rotation curve observed by Capaccioli et al. (1993).Comment: 18 pages, 22 figures, accepted for publication in MNRA
Tracing the relation between black holes and dark haloes
We present new velocity dispersion measurements for a set of 12 spiral
galaxies and use them to derive a more accurate V_c - sigma relation which
holds for a wide morphological range of galaxies. Combined with the M_BH -
sigma relation, this relation can be used as a tool to estimate supermassive
black hole (SMBH) masses by means of the asymptotic circular velocity. Together
with the Tully-Fisher relation, it serves as a constraint for galaxy formation
and evolution models.Comment: 2 pages, 2 figures, to appear in Proc. IAU Symp. 220, "Dark Matter in
Galaxies" eds. S. Ryder, D.J. Pisano, M. Walker, & K. Freeman (San Francisco:
ASP
Completely analytical families of anisotropic gamma-models
We present new analytical distribution functions for anisotropic spherical
galaxies. They have the density profiles of the gamma-models, which allow a
wide range of central density slopes, and are widely used to fit elliptical
galaxies and the bulges of spiral galaxies. Most of our models belong to two
two-parameter families. One of these parameters is the slope gamma of the
central density cusp. The other allows a wide range of varying radial and
tangential anisotropies, at either small or large radii. We give analytical
formulas for their distribution functions, velocity dispersions, and the manner
in which energy and transverse velocity are distributed between orbits. We also
give some of their observable properties, including line-of-sight velocity
profiles which have been computed numerically. Our models can be used to
provide a useful tool for creating initial conditions for N-body and Monte
Carlo simulations.Comment: 21 pages, 15 figures, accepted for publication in MNRA
Dynamical models linking BH masses and DM content
We investigate the relation between the dark matter distribution of galaxies
and their central supermassive black holes which is suggested by the v_c-sigma
relation. Since early-type galaxies appear to have larger black holes than
late-type ones, we look for an equivalent pattern in the dark matter
distribution as a function of Hubble type. To achieve our goal we use a
state-of-the-art modelling code that allows a variety of geometries to be
fitted to a combination of radio and optical observations of galaxies with
different morphology.Comment: 2 pages, 2 figures, contributed paper to Proceedings of the
Conference "Growing Black Holes" held in Garching, Germany, June 21-25, 2004,
edited by A. Merloni, S. Nayakshin and R. Sunyaev, Springer-Verlag series of
"ESO Astrophysics Symposia
N-body/SPH study of the evolution of dwarf galaxies in a cluster environment
Using an N-body/SPH code, we explore the scenario in which a dwarf elliptical
galaxy (dE) is subjected to ram-pressure stripping due to the intracluster
medium (ICM). Our simulations show that while (i) smaller dEs lose their ISM
almost immediately after entering the cluster, (ii) more massive dEs are able
to retain their gas for considerable timespans.Comment: 1 page, no figures, poster contribution to the Splinter Meeting
"Galaxies in interaction" at the joint meeting of the Czech Astronomical
Society and the Astronomische Gesellschaft (20-25 Sept. 2004, Prague, Czech
Republic
Dark matter halos around elliptical galaxies: how reliable is the stellar kinematical evidence ?
Hierarchical models of galaxy formation and various observational evidence
suggest that elliptical galaxies are, like disk galaxies, embedded in massive
dark matter halos. Stellar kinematics are considered the most important tracer
for this dark halo at a few effective radii. Using detailed modeling
techniques, several authors have recently presented stellar kinematical
evidence of a dark halo for a number of elliptical galaxies. In these modeling
techniques, dust attenuation (absorption and scattering of starlight by dust
grains) has not been taken into account. Nevertheless, elliptical galaxies
contain a significant amount of interstellar dust, which affects all observable
quantities, including the observed kinematics. We constructed a set of
dynamical models for elliptical galaxies, in which dust attenuation is included
through a Monte Carlo technique. We find that a dust component, shallower than
the stellar distribution and with an optical depth of order unity, affects the
observed kinematics significantly, in the way that it mimics the presence of a
dark halo. If such dust distributions are realistic in elliptical galaxies, we
are faced with a new mass-dust degeneracy. Taking dust into account in
dynamical modeling procedures will hence reduce or may even eliminate the need
for a dark matter halo at a few effective radii.Comment: 5 pages, 4 figures, accepted for publication in ApJ Letters. Uses
emulateapj5.sty. Typos are correcte
The Hernquist model revisited: completely analytical anisotropic dynamical models
Simple analytical models, such as the Hernquist model, are very useful tools
to investigate the dynamical structure of galaxies. Unfortunately, most of the
analytical distribution functions are either isotropic or of the
Osipkov-Merritt type, and hence basically one-dimensional. We present three
different families of anisotropic distribution functions that self-consistently
generate the Hernquist potential-density pair. These families have constant,
increasing and decreasing anisotropy profiles respectively, and can hence
represent a wide variety of orbital structures. For all of the models
presented, the distribution function and the velocity dispersions can be
written in terms of elementary functions. These models are ideal tools for a
wide range of applications, in particular to generate the initial conditions
for N-body or Monte Carlo simulations.Comment: 14 pages, 7 figures, accepted for publication in A&A - formulae (51)
and (54) and figure 4 correcte
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