SPH simulations of the chemical evolution of bulges

We have implemented a chemical evolution model on the parallel AP3M+SPH DEVA code which we use to perform high resolution simulations of spiral galaxy formation. It includes feedback by SNII and SNIa using the Qij matrix formalism. We also include a diffusion mechanism that spreads newly introduced metals. The gas cooling rate depends on its specific composition. We study the stellar populations of the resulting bulges finding a potential scenario where they seem to be composed of two populations: an old, metal poor, $\alpha$-enriched population, formed in a multiclump scenario at the beginning of the simulation and a younger one, formed by slow accretion of satellites or gas, possibly from the disk due to instabilities.Comment: 2 pages, 3 figures. Proceedings of IAUS 245 "Formation and Evolution of Galaxy Bulges

Lagrangian Volume Deformations around Simulated Galaxies

We present a detailed analysis of the local evolution of 206 Lagrangian Volumes (LVs) selected at high redshift around galaxy seeds, identified in a large-volume $\Lambda$ cold dark matter ($\Lambda$CDM) hydrodynamical simulation. The LVs have a mass range of $1 - 1500 \times 10^{10} M_\odot$. We follow the dynamical evolution of the density field inside these initially spherical LVs from $z=10$ up to $z_{\rm low} = 0.05$, witnessing highly non-linear, anisotropic mass rearrangements within them, leading to the emergence of the local cosmic web (CW). These mass arrangements have been analysed in terms of the reduced inertia tensor $I_{ij}^r$, focusing on the evolution of the principal axes of inertia and their corresponding eigendirections, and paying particular attention to the times when the evolution of these two structural elements declines. In addition, mass and component effects along this process have also been investigated. We have found that deformations are led by dark matter dynamics and they transform most of the initially spherical LVs into prolate shapes, i.e. filamentary structures. An analysis of the individual freezing-out time distributions for shapes and eigendirections shows that first most of the LVs fix their three axes of symmetry (like a skeleton) early on, while accretion flows towards them still continue. Very remarkably, we have found that more massive LVs fix their skeleton earlier on than less massive ones. We briefly discuss the astrophysical implications our findings could have, including the galaxy mass-morphology relation and the effects on the galaxy-galaxy merger parameter space, among others.Comment: 23 pages, 20 figures. Minor editorial improvement

Lagrangian formulation of classical fields within Riemann-Liouville fractional derivatives

The classical fields with fractional derivatives are investigated by using the fractional Lagrangian formulation.The fractional Euler-Lagrange equations were obtained and two examples were studied.Comment: 9 page

Conservation Laws in Smooth Particle Hydrodynamics: the DEVA Code

We describe DEVA, a multistep AP3M-like-SPH code particularly designed to study galaxy formation and evolution in connection with the global cosmological model. This code uses a formulation of SPH equations which ensures both energy and entropy conservation by including the so-called \bn h terms. Particular attention has also been paid to angular momentum conservation and to the accuracy of our code. We find that, in order to avoid unphysical solutions, our code requires that cooling processes must be implemented in a non-multistep way. We detail various cosmological simulations which have been performed to test our code and also to study the influence of the \bn h terms. Our results indicate that such correction terms have a non-negligible effect on some cosmological simulations, especially on high density regions associated either to shock fronts or central cores of collapsed objects. Moreover, they suggest that codes paying a particular attention to the implementation of conservation laws of physics at the scales of interest, can attain good accuracy levels in conservation laws with limited computational resources.Comment: 36 pages, 10 figures. Accepted for publication in The Astrophysical Journa

Hydrodynamic Approach to the Evolution of Cosmic Structures II: Study of N-body Simulations at z=0

We present a series of cosmological N-body simulations which make use of the hydrodynamic approach to the evolution of structures (Dominguez 2000). This approach addresses explicitly the existence of a finite spatial resolution and the dynamical effect of subresolution degrees of freedom. We adapt this method to cosmological simulations of the standard LCDM structure formation scenario and study the effects induced at redshift z=0 by this novel approach on the large-scale clustering patterns as well as (individual) dark matter halos. Comparing these simulations to usual N-body simulations, we find that (i) the new (hydrodynamic) model entails a proliferation of low--mass halos, and (ii) dark matter halos have a higher degree of rotational support. These results agree with the theoretical expectation about the qualitative behaviour of the "correction terms" introduced by the hydrodynamic approach: these terms act as a drain of inflow kinetic energy and a source of vorticity by the small-scale tidal torques and shear stresses.Comment: 18 pages, 17 figs, MNRAS in press, article with full resolution figures avaialble at http://www.aip.de/People/AKnebe/page2/page2.htm