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

Initial SB Final SB

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).


SAURON kin PN

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.

NMAGIC

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