Theoretical astrophysics and plasma physics at RPC

Abstract:

In galaxies like the Milky Way, cold (~ 10^4 K) gas ejected from the disc by stellar activity (the so-called galactic-fountain gas) is expected to interact with the virial-temperature (~ 10^6 K) gas of the corona. The associated transfer of momentum between cold and hot gas has important consequences for the dynamics of both gas phases. We quantify the effects of such an interaction using hydrodynamical simulations of cold clouds travelling through a hot medium at different relative velocities. Our main finding is that there is a velocity threshold between clouds and corona, of about 75 km/s, below which the hot gas ceases to absorb momentum from the cold clouds. It follows that in a disc galaxy like the Milky Way a static corona would be rapidly accelerated: the corona is expected to rotate and to lag, in the inner regions, by ~ 80-120 km/s with respect to the cold disc. We also show how the existence of this velocity threshold can explain the observed kinematics of the cold extra-planar gas.

Abstract:

We present here a fast code for creating a synthetic survey of the Milky Way. Given one or more color-magnitude bounds, a survey size, and geometry, the code returns a catalog of stars in accordance with a given model of the Milky Way. The model can be specified by a set of density distributions or as an N-body realization. We provide fast and efficient algorithms for sampling both types of models. As compared to earlier sampling schemes which generate stars at specified locations along a line of sight, our scheme can generate a continuous and smooth distribution of stars over any given volume. The code is quite general and flexible and can accept input in the form of a star formation rate, age-metallicity relation, age-velocity-dispersion relation, and analytic density distribution functions. Theoretical isochrones are then used to generate a catalog of stars, and support is available for a wide range of photometric bands. As a concrete example, we implement the Besançon Milky Way model for the disk. For the stellar halo we employ the simulated stellar halo N-body models of Bullock & Johnston. In order to sample N-body models, we present a scheme that disperses the stars spawned by an N-body particle, in such a way that the phase-space density of the spawned stars is consistent with that of the N-body particles. The code is ideally suited to generating synthetic data sets that mimic near future wide area surveys such as GAIA, LSST, and HERMES. As an application we study the prospect of identifying structures in the stellar halo with a simulated GAIA survey. We plan to make the code publicly available. © 2011. The American Astronomical Society. All rights reserved.