Theoretical astrophysics and plasma physics at RPC

Abstract:

We study the eccentricity distribution of a thick-disc sample of stars (defined as those withVy > 50kms-1and1 < |z|/kpc < 3) observed in the Radial Velocity Experiment (RAVE). We compare this distribution with those obtained in four simulations of galaxy formation taken from the literature as compiled by Sales et al. Each simulation emphasizes different scenarios for the origin of such stars (satellite accretion, heating of a pre-existing thin disc during a merger, radial migration, and gas-rich mergers). We find that the observed distribution peaks at low eccentricities and falls off smoothly and rather steeply to high eccentricities. This finding is fairly robust to changes in distances and to plausible assumptions about thin-disc contamination. Our results favour models where the majority of stars formed in the Galaxy itself on orbits of modest eccentricity and disfavour the pure satellite accretion case. A gas-rich merger origin where most of the stars form 'in situ' appears to be the most consistent with our data. © 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Abstract:

Many of the proposed science cases for extremely large telescopes (ELT) are only possible because of the unprecedented sensitivity and spatial resolution due to advanced, e.g. tomographic and multi conjugate, adaptive optic (AO) systems. Current AO systems on 8-10 m telescopes work best at wavelengths longward of 1 μm with Strehl ratios ≥ 15%. At red-optical wavelengths, e.g. in the I band (0.8 μm), the Strehl ratio is at best a few percent. The AO point spread function (PSF) typically has a diffraction-limited core superimposed on the seeing halo, however, for a 5% Strehl ratio the core has a very low intensity above the seeing halo. At an ELT, due to a 3-4 times higher angular resolution, the diffraction limited PSF core of only 5% Strehl ratio stands more prominently atop the shallow seeing halo leading to almost diffraction limited image quality even at low Strehl ratios. Prominent ELT science cases that use the Calcium triplet can exploit this gain in spatial resolution in the red-optical: stellar populations in dense environments or crowded fields; and the case of intermediate mass black holes in nuclear and globular stellar clusters, as well as (super-) massive black holes in galaxies.