Made-to-measure
Dynamical Modeling of Galaxies with
NMAGIC
Introduction
Recent results Publications MPE OPINAS Dynamics Group
Introduction
The goal of dynamical modeling is to recover from observational data
the distribution of orbits for the galaxy's stars, and the
gravitational potential in which they move. Through dynamical modeling,
one can determine the mass of the supermassive black hole in the
galaxy's center, or the amount of dark matter in its
outskirts. <more
on dynamical modeling>
The idea of the made-to-measure (M2M) method is to find a particle model
that
faithfully represents the galaxy observations; see Syer
&
Tremaine, 1996, De
Lorenzi,
Debattista, Gerhard & Sambhus, 2007. I.e., when the
particle
model is "observed" in the same way as the galaxy, its surface density
distribution and projected kinematics should match those of the galaxy.
Once this is achieved, the model can be used to learn about the
intrinsic structure of the galaxy. The parallel code NMAGIC is an
implementation of a made-to-measure technique suitable for finding such
a model from a given set of observational data, starting from an
initial particle distribution. <more
on the M2M
method here>
Example for NMAGIC at work:
|
Before
|
After
|
 |
 |
|
Figure 1:
Evolution of an an initially
spherical model consisting of 1.8 million particles towards a triaxial
target galaxy. The panels show contour plots of the surface brightness
distribution. The black solid lines represent the particle model and
the red solid lines correspond to the triaxial target galaxy. The left
panel compares the initial model with the target galaxy and the right
panel shows the final model. The match is excellent.
|
Applications of NMAGIC
Dark matter halos in the "naked" elliptical galaxies NGC 3379 and NGC
4697 (De
Lorenzi et al. 2008, 2009).
 |
 |
|
Figure 2:
Comparison of NMAGIC dynamical
particle models with kinematic data for NGC 3379. Left: Comparison of
axisymmetric and weakly triaxial models with SAURON kinematic data for
NGC 3379 (top panel, Shapiro
et
al. 2006). Following panels are for models A90, D90, DR.
Model A90
has all the mass in the stars, while the later two models include a
massive halo. Right: Comparison of the radial velocity dispersion
profile from the PN.S data (Douglas
et
al. 2007) with the oblate and weakly triaxial particle models.
|
In conclusion: the kinematic data for NGC 3379 are consistent with a
variety of dark matter halos, including some that are predicted by
merger models in ΛCDM cosmology. NGC 3379 need not be
"naked". <more on
NGC 3379>
Recent results
See also page on
outer haloes of elliptical galaxies.
Publications
de Lorenzi, F., Gerhard, O., Coccato, L., Arnaboldi, M., Capaccioli, M., Douglas, N. G., et al. 2009, MNRAS, 395, 76.
Dearth of dark matter or massive dark halo? Mass-shape-anisotropy degeneracies revealed by NMAGIC dynamical models of the elliptical
galaxy NGC 3379. 2009MNRAS.395...76D
de Lorenzi, F., Gerhard, O., Saglia, R. P., Sambhus, N., Debattista, V. P., Pannella, M., et al. 2008, MNRAS, 385, 1729.
Dark matter content and internal dynamics of NGC 4697: NMAGIC particle models from slit data and planetary nebula velocities. 2008MNRAS.385.1729D
de Lorenzi, F., Debattista, V. P., Gerhard, O., Sambhus, N. 2007, MNRAS, 376, 71.
NMAGIC: a fast parallel implementation of a χ2-made-to-measure algorithm for modelling observational data. 2007MNRAS.376...71D
Bissantz, N., Debattista, V. P., Gerhard, O. 2004, ApJ, 601, L155.
Large-Scale Model of the Milky Way: Stellar Kinematics and the Microlensing Event Timescale Distribution in the Galactic Bulge. 2004ApJ...601L.155B
