67 research outputs found
On the reliability of the black hole mass and mass to light ratio determinations with Schwarzschild models
In this Letter, we investigate the claim of Valluri et al. (2003), namely
that the use of Schwarzschild dynamical (orbit-based) models leads to an
indeterminacy regarding the estimation of the free parameters like the central
black hole mass and the stellar mass-to-light ratio of the galaxy under study.
We examine this issue with semi-analytic two-integral models, which are not
affected by the intrinsic degeneracy of three-integral systems. We however
confirm the Valluri et al. result, and observe the so-called widening of the
chi2 contours as the orbit library is expanded. We also show that, although
two-dimensional data coverage help in constraining the orbital structure of the
modelled galaxy, it does not in principle solve the indeterminacy issue, which
mostly originates from the discretization of such an inverse problem. We show
that adding regularization constraints stabilizes the confidence level contours
on which the estimation of black hole mass and stellar mass-to-light ratio are
based. We therefore propose to systematically use regularization as a tool to
prevent the solution to depend on the orbit library. Regularization, however,
introduces an unavoidable bias on the derived solutions. We hope that the
present Letter will trigger some more research directed at a better
understanding of the issues addressed here.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letter
Axisymmetric dynamical models for SAURON and OASIS observations of NGC3377
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
Perfiles de gratitud, necesidades psicológicas y su relación con la resiliencia en estudiantes no tradicionales
The aim of this research was to identify gratitude profiles, basic psychological needs in relation with resilience of non-traditional students adults worker. This study was cross-sectional, descriptive, non-experimental in design and a cluster analysis was used. A total 114 students from a local university answered 3 instruments to evaluate these variables. This study reports 4 profiles and showed that only one significantly differs in resilience from the others, featuring high levels of gratitude and psychological needs. Profiles that are underperforming in the variables obtained lower resilience. One of them, equivalent to 10.5% of the students, also reports a lower need for autonomy. This study suggests that interventions must be focused on young students to strengthen their need for autonomy and resilience.El objetivo del estudio fue identificar perfiles de gratitud, necesidades psicológicas básicas y su relación con la resiliencia en estudiantes no tradicionales adultos-trabajadores. Se utilizó un diseño no experimental, transversal, descriptivo y un análisis de clústeres; 114 estudiantes universitarios respondieron tres instrumentos para evaluar las variables. Los resultados muestran 4 perfiles, sólo uno se diferencia significativamente en resiliencia, en ventaja de los otros, presentando altos niveles en gratitud y necesidades psicológicas. Los tres perfiles más desfavorecidos en las variables obtienen menor resiliencia. Uno de ellos, equivalente a un 10,5% de los estudiantes, presenta también baja necesidad de autonomía. Se concluye que las intervenciones deberían estar focalizadas en los estudiantes jóvenes, para fortalecer su necesidad de autonomía y resiliencia
Axisymmetric dynamical models for SAURON and OASIS observations of NGC 3377
We present a unique set of nested stellar kinematical maps of NGC 3377
obtained with the integral-field spectrographs OASIS and SAURON. We then
construct general axisymmetric dynamical models for this galaxy, based on the
Schwarzschild numerical orbit superposition technique applied to these
complementary measurements. We show how these two datasets constrain the mass
of the central massive object and the overall mass-to-light ratio of the galaxy
by probing the inner and outer regions respectively. The simultaneous use of
both datasets leads us to confirm the presence of a massive black hole with a
mass of M_{BH} = 7_{-5}^{+4} 10^{7} M_\sun (99.7% confidence level), with a
best-fit stellar mass-to-light ratio (for an assumed
edge-on inclination).Comment: 15 pages, 14 figures. Accepted for publication in A&A (original fig.
layout, letterpaper
Axisymmetric Three-Integral Models for Galaxies
We describe an improved, practical method for constructing galaxy models that
match an arbitrary set of observational constraints, without prior assumptions
about the phase-space distribution function (DF). Our method is an extension of
Schwarzschild's orbit superposition technique. As in Schwarzschild's original
implementation, we compute a representative library of orbits in a given
potential. We then project each orbit onto the space of observables, consisting
of position on the sky and line-of-sight velocity, while properly taking into
account seeing convolution and pixel binning. We find the combination of orbits
that produces a dynamical model that best fits the observed photometry and
kinematics of the galaxy. A key new element of this work is the ability to
predict and match to the data the full line-of-sight velocity profile shapes. A
dark component (such as a black hole and/or a dark halo) can easily be included
in the models.
We have tested our method, by using it to reconstruct the properties of a
two-integral model built with independent software. The test model is
reproduced satisfactorily, either with the regular orbits, or with the
two-integral components. This paper mainly deals with the technical aspects of
the method, while applications to the galaxies M32 and NGC 4342 are described
elsewhere (van der Marel et al., Cretton & van den Bosch). (abridged)Comment: minor changes, accepted for publication in the Astrophysical Journal
Supplement
The velocity and mass distribution of clusters of galaxies from the CNOC1 cluster redshift survey
In the context of the CNOC1 cluster survey, redshifts were obtained for
galaxies in 16 clusters. The resulting sample is ideally suited for an analysis
of the internal velocity and mass distribution of clusters. Previous analyses
of this dataset used the Jeans equation to model the projected velocity
dispersion profile. However, the results of such an analysis always yield a
strong degeneracy between the mass density profile and the velocity dispersion
anisotropy profile. Here we analyze the full (R,v) dataset of galaxy positions
and velocities in an attempt to break this degeneracy. We build an `ensemble
cluster' from the individual clusters under the assumption that they form a
homologous sequence. To interpret the data we study a one-parameter family of
spherical models with different constant velocity dispersion anisotropy. The
best-fit model is sought using a variety of statistics, including the overall
likelihood of the dataset. Although the results of our analysis depend slightly
on which statistic is used to judge the models, all statistics agree that the
best-fit model is close to isotropic. This result derives primarily from the
fact that the observed grand-total velocity histogram is close to Gaussian,
which is not expected to be the case for a strongly anisotropic model. The
best-fitting models have a mass-to-number-density ratio that is approximately
independent of radius over the range constrained by the data. They also have a
mass-density profile that is consistent with the dark matter halo profile
advocated by Navarro, Frenk & White, in terms of both the profile shape and the
characteristic scale length. This adds important new weight to the evidence
that clusters do indeed follow this proposed universal mass density profile.
[Abridged]Comment: 37 pages, LaTeX, with 11 PostScript figures. Accepted by the
Astronomical Journal, to appear in the May 2000 issue. This replacement
version contains an additional Appendix and one additional Figure with
respect to the version submitted to astro-ph originall
Supermassive Black Holes in Galactic Nuclei: Past, Present and Future Research
This review discusses the current status of supermassive black hole research,
as seen from a purely observational standpoint. Since the early '90s, rapid
technological advances, most notably the launch of the Hubble Space Telescope,
the commissioning of the VLBA and improvements in near-infrared speckle imaging
techniques, have not only given us incontrovertible proof of the existence of
supermassive black holes, but have unveiled fundamental connections between the
mass of the central singularity and the global properties of the host galaxy.
It is thanks to these observations that we are now, for the first time, in a
position to understand the origin, evolution and cosmic relevance of these
fascinating objects.Comment: Invited Review, 114 pages. Because of space requirements, this
version contains low resolution figures. The full resolution version can be
downloaded from http://www.physics.rutgers.edu/~lff/publications.htm
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