T. Naab — Page 6 | Searcharxiv

arXiv2002

Collisional Stellar Dynamics, Gas Dynamics and Special Purpose Computing

Challenging stellar dynamical problems, such as the study of gravothermal oscillations in star clusters, have in the past initiated the very successful building of GRAPE special purpose computers. It is discussed, that present day tasks such as the formation and evolution of galactic nuclei with one or more massive black holes and the coupled stellar and gas dynamical processes in the formation of nuclei and star clusters, demand a new kind of hybrid architecture, using both GRAPE and a reconfigurable logics board called RACE. For such a system we have developed first implementations and floating point performance studies in the case of the SPH algorithm (smoothed particle hydrodynamics), which will be of great advantage for SPH modelling and also for direct $N$-body simulations using the more efficient Ahmad-Cohen neighbour schemes.

astro-ph↗

arXiv2001

The kinematics of 3:1-merger remnants and the formation of low-luminosity elliptical galaxies

We test the formation of low-luminosity elliptical galaxies through collisionless mergers of unequal-mass disk galaxies. The kinematic properties of a small survey of simulated merger end-products with initial disk mass ratios of 3:1 is compared to a sample of seven low-luminosity galaxies observed by Rix et al. that were chosen photometrically to be "ellipticals". In this paper, we go beyond a comparison in terms of global properties (using one number to characterize a model or a galaxy e.g. , ellipticity at some fixed radius or central velocity dispersion) and examine the detailed kinematics as function of galactocentric distance. The merger remnants are ``observed'' through a slit along the major and minor axis, using a pixel binning and slit width similar to the one used during the spectroscopic observations. We compare the rotational support (v/sigma) of the merger remnants, the normalized rotation on the minor axis and the major axis Gauss-Hermite moments h3, to that of the observed galaxies. The N-body remnants are very flattened when viewed edge-on ( = 0.6) and should be inclined before making a fair comparison with the Rix et al. data set (which has = 0.3). When the merger remnants are appropriately inclined, their v/sigma profiles rise slower than the observed ones. Note that even when the remnants are viewed edge-on, the v/sigma profiles do not match the observations. The detailed comparison of the observations with purely collisionless 3:1-merger remnants suggests that this kind of dissipationless merger is not likely to be the dominant formation channel for low-luminosity elliptical galaxies. (abridged)

astro-ph↗