Dark Matter Halo Structure in CDM Hydrodynamical Simulations

We have carried out a comparative analysis of the properties of dark matter halos in N-body and hydrodynamical simulations. We analyze their density profiles, shapes and kinematical properties with the aim of assessing the effects that hydrodynamical processes might produce on the evolution of the dark matter component. The simulations performed allow us to reproduce dark matter halos with high resolution, although the range of circular velocities is limited. We find that for halos with circular velocities of $[150-200] km s^{-1}$ at the virial radius, the presence of baryons affects the evolution of the dark matter component in the central region modifying the density profiles, shapes and velocity dispersions. We also analyze the rotation velocity curves of disk-like structures and compare them with observational results.Comment: 28 pages, 15 figures (figures 3ab sent by request), 2 tables. Accepted for publication MNRA

Measuring galaxy segregation using the mark connection function

(abridged) The clustering properties of galaxies belonging to different luminosity ranges or having different morphological types are different. These characteristics or `marks' permit to understand the galaxy catalogs that carry all this information as realizations of marked point processes. Many attempts have been presented to quantify the dependence of the clustering of galaxies on their inner properties. The present paper summarizes methods on spatial marked statistics used in cosmology to disentangle luminosity, colour or morphological segregation and introduces a new one in this context, the mark connection function. The methods used here are the partial correlation functions, including the cross-correlation function, the normalised mark correlation function, the mark variogram and the mark connection function. All these methods are applied to a volume-limited sample drawn from the 2dFGRS, using the spectral type as the mark. We show the virtues of each method to provide information about the clustering properties of each population, the dependence of the clustering on the marks, the similarity of the marks as a function of the pair distances, and the way to characterise the spatial correlation between the marks. We demonstrate by means of these statistics that passive galaxies exhibit stronger spatial correlation than active galaxies at small scales (r <20 Mpc/h). The mark connection function, introduced here, is particularly useful for understanding the spatial correlation between the marks.Comment: 6 pages, 5 figures, accepted for publication in Astronomy and Astrophysic

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

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

Winter sowing and higher populations as dry-farming strategies on sunflower crop (Helianthus annuus L.)

Sunflower is sown in early spring (March-April) under Mediterranean dryland conditions. Plant development is coincidental with increasing air temperature and crop ET and usually reproduction occurs under water and temperature stresses, resulting in severe yield limitations (Downes 1975, Carvalho et al 1990, 1991). As a strategy of stress avoidance during the reproductive stages winter sowing (late December and January) has been successfully tested (Vesperinas et al 1991, Ordonez 1990). This experiment tested the potential advantage in anticipating sowing date to late December or January, and in increasing plant population in order to use soil water more efficiently

Disc-like Objects in Hierarchical Hydrodynamical Simulations: Comparison with Observations

We present results from a careful and detailed analysis of the structural and dynamical properties of a sample of 29 disc-like objects identified at z=0 in three AP3M-SPH fully consistent cosmological simulations. These simulations are realizations of a CDM hierarchical model, where an inefficient Schmidt law-like algorithm to model the stellar formation process has been implemented. We focus on properties that can be constrained with available data from observations of spiral galaxies, namely, the bulge and disc structural parameters and the rotation curves. Comparisons with data from Broeils (1992), de Jong (1996) and Courteau (1996, 1997) give satisfactory agreement, in contrast with previous findings using other codes. This suggests that the stellar formation implementation we have used has succeded in forming compact bulges that stabilize disc-like structures in the violent phases of their assembly, while in the quiescent phases the gas has cooled and collapsed according with the Fall & Efstathiou standard model of disc formation.Comment: 22 pages, LaTeX; 14 figures; references updated. MNRAS, in pres