Moving Groups and a Dynamical Galaxy Model

State of the art

Galactic Dynamics is traced by the motions of the Milky Way’s stars and gas. Gaia will focus on stellar motions, which are key for uncovering the properties of the different stellar components of our Galaxy such as the size, mass, density of the thin and thick disk. Galactic dynamics are an excellent means of deriving the detailed mass distribution of the Milky Way and of constraining the distribution and amount of dark matter. Dynamics are also a vital tool for uncovering stellar streams in phase space and for finding signatures of ancient accretion events.

Description of the work:

Recent studies of the stellar streams in the galactic disk of the Milky Way, up to now restricted to the solar neighborhood, have demonstrated that this kinematic structures will be a powerful tool to constrain the large scale structure of the MW in the Gaia era, both in its present and past form (Antoja et al. 2009). Gaia and complementary on-ground data will provide a deep insight on the kinematics, evolutionary state and chemical composition of the stellar members of these stellar streams, not only in the solar neighbourhood but also at large galactocentric distances. From that, a huge progress is expected in our knowledge of the MW galactic potential. At present, the number of spiral patterns in our MW and their shapes and speeds have not been unambiguously determined (Vallee et la., 2008, among others). Even more, the relation between spiral and bar patterns is not well understood (Athanassoula et al., 2008), and an important work is pending to evaluate the kinematic imprints of a secular evolution of the bar and the spiral structures (Minchev et al., 2009).

As mentioned, several possibilities for the origin of the moving groups present in the solar neighbourhood are nowadays considered: 1) Cluster and star complex disruption; 2) Orbital and resonant effects of the non-axisiymmetric structure of the MW (spiral arms and bar), 3) Tidal debris due to accretion of satellite galaxies, 4) Effects on the disk due to a massive merger, and/or 5) wave in the velocity plane in an unrelaxed MW disk among others. A deep study on these complex scenarios requires a rigorous training on both, MK galaxy modeling and the use of robust statistical tools for data treatment on large sets of observed and simulated data in a N-dimensional space.

Several existing galaxy modeling tools shall be improved and adapted to fully exploit the exiting Gaia data: 1) analytical approximations from test particle orbit computation through the derivation of more realistic galactic potential (Collaboration with IAC; structure of the internal disc components of the MW), 2) large N-body simulations developing bar and spiral arms, to be able to study the detailed analysis of the kinematics associated to these resonant streams mentioned above; 3) chemodynamical modeling including gas-dynamics, chemical enrichment, mixing and metal cooling gas dynamics (Collaboration with MSSL/UCL: ) to trace the star formation history and their motion on time dependent model. We shall be able to realistically predict the growth of the non-axissymetric component ofs the MW and the role of the stellar streams in this context. Furthermore, the imprints of the simulated stellar streams when combining the above mentioned models (hybrid approach) has to be explored in the stellar phase space distribution considering position, kinematics, chemical composition and evolutionary state of the stellar populations present in our galactic disk and to be observed by Gaia.

Training programme on:

Training on multivariate data analysis techniques for the detection and characterization of the stellar streams (assistance to the Lund’s school on Statistics). At the first stage of the project we will evaluate the future Gaia capabilities to characterize moving groups on a wide range of galactocentric radii. Research teams contributing to this project are deeply involved in the Gaia Mission preparation. Gaia Universe Model Snapshot (GUMS, DPAC-CU2-Simulations Working Group, lead by the UB team) will be used. The ESR will learn also from the developing Calibration tasks on RVS (as part of CU6) being undertaken at MSSL/UCL (note that radial velocities are critical in our project). Understanding the Gaia capability (including CCD errors, radiation damage and etc...) would be invaluable for predicting what Gaia can achieve after combining with the theoretical predictions. These training activities are mandatory to treat rigorously the full set Gaia and complementary on-ground data, the last one providing accurate radial velocities and detailed chemical abundances from high resolution spectroscopy

We propose the derivation of a more realistic potential for the internal disk non-axissymetric structures. Training on IR techniques to elucidate the true nature of the stellar components of these structures will be undertaken in the IAC (associate node). NIR star counts based large surveys (GLIMPSE, VISTA, UKIRT) and spectroscopic follow up using EMIR (GranTeCan) are milestones for the goal proposed here.

Training on new hybrid approaches (N-body + test particle + SPH + chemodynamical modeling) to be applied to our MW. This approach is very computationally intensive and the improvement of the present supercomputing techniques is mandatory (Barcelona Supercomputing Center will be used under e-Ciencia Consolider Programme, MICINN). Existing simulations are limited in the number of particles in the galactic disk, thus a massively parallel computational approach is required to resolve the structure of the phase space – including accurate kinematics - to match Gaia observational data. Furthermore, although the proposed simulations can be used to explore non-equilibrium dynamical processes, other techniques such as test-particle integration methods will allow us to investigate on a larger range of initial conditions (birthplaces of stars). A secondment of the ESR student for 6 months is proposed at MSSL/UCL).

The present project will joint efforts from researches on two complementary disciplines: theoretical dynamics and chemical evolution (Kawata, UCL) and computational astronomy ( MareNostrum).

Duration:

The ESR will be for 3 years at the Universitat de Barcelona

Mobility within the GREAT/ITN:

The ESR will spend:

• 6 months at the Mullar Space Science Laboratory MSSL to study the chemo-dynamical modelling with GCD+
• 4 months at the Instituto de Astrofisica de Canarias IAC for the Galactic dynamics modelling.