Galaxy formation and evolution

Abstract:

Under ideal MHD conditions the magnetic field strength should be correlated with density in the interstellar medium ( ISM). However, observations indicate that this correlation is weaker than expected. Ambipolar diffusion can decrease the flux-to-mass ratio in weakly ionized media; however, it is generally thought to be too slow to play a significant role in the ISM except in the densest molecular clouds. Turbulence is often invoked in other astrophysical problems to increase transport rates above the ( very slow) diffusive values. Building on analytical studies, we test with numerical models whether turbulence can enhance the ambipolar diffusion rate sufficiently to explain the observed weak correlations. The numerical method is based on a gas-kinetic scheme with very low numerical diffusivity, thus allowing us to separate numerical and physical diffusion effects.

Abstract:

We present a summary of high-spatial resolution follow-up observations of the elliptical (E) and lenticular (SO) galaxies in the SAURON survey using the OASIS integral field spectrograph. The OASIS observations explore the central 8" x 10" regions of these galaxies using a spatial sampling four times higher than SAURON, often revealing previously undiscovered features. Around 75% (31/48) of the SAURON E/SOs with central velocity dispersion greater than or similar to 120 kin s(-1) were observed with OASIS, covering well the original SAURON representative sample. We present here an overview of this follow-up survey, and some preliminary results on individual objects, including a previously unreported counter-rotating core in NGC4382; the decoupled stellar and gas velocity fields of NGC 2768; and the strong age gradient towards the centre of NGC 3489.