Arturo Serna

Chemical evolution of galaxies – I. A composition-dependent SPH model for chemical evolution and cooling

We describe an smooth particle hydrodynamics (SPH) model for chemical enrichment and radiative cooling in cosmological simulations of structure formation. This model includes: (i) the delayed gas restitution from stars by means of a probabilistic approach designed to reduce the statistical noise and, hence, to allow for the study of the inner chemical structure of objects with moderately high numbers of particles; (ii) the full dependence of metal production on the detailed chemical composition of stellar particles by using, for the first time in SPH codes, the Q i j matrix formalism that relates each nucleosynthetic product to its sources and (iii) the full dependence of radiative cooling on the detailed chemical composition of gas particles, achieved through a fast algorithm using a new metallicity parameter ζ(T) that gives the weight of each element on the total cooling function. The resolution effects and the results obtained from this SPH chemical model have been tested by comparing its predictions in different problems with known theoretical solutions. We also present some preliminary results on the chemical properties of elliptical galaxies found in self-consistent cosmological simulations. Such simulations show that the above ζ-cooling method is important to prevent an overestimation of the metallicity-dependent cooling rate, whereas the Q ij formalism is important to prevent a significant underestimation of the [a/Fe] ratio in simulated galaxy-like objects.

A two-phase scenario for bulge assembly in ΛcDM cosmologies

We analyze and compare the bulges of a sample of L * spiral galaxies in hydrodynamical simulations in a cosmological context, using two different codes, P-DEVA and GASOLINE. The codes regulate star formation in very different ways, with P-DEVA simulations inputting low star formation efficiency under the assumption that feedback occurs on subgrid scales, while the GASOLINE simulations have feedback that drives large-scale outflows. In all cases, the marked knee shape in mass aggregation tracks, corresponding to the transition from an early phase of rapid mass assembly to a later slower one, separates the properties of two populations within the simulated bulges. The bulges analyzed show an important early starburst resulting from the collapse-like fast phase of mass assembly, followed by a second phase with lower star formation, driven by a variety of processes such as disk instabilities and/or mergers. Classifying bulge stellar particles identified at z = 0 into old and young according to these two phases, we found bulge stellar sub-populations with distinct kinematics, shapes, stellar ages, and metal contents. The young components are more oblate, generally smaller, more rotationally supported, with higher metallicity and less alpha-element enhanced than the old ones. These results are consistent with the current observational status of bulges, and provide an explanation for some apparently paradoxical observations, such as bulge rejuvenation and metal-content gradients observed. Our results suggest that bulges of L * galaxies will generically have two bulge populations that can be likened to classical and pseudo-bulges, with differences being in the relative proportions of the two, which may vary due to galaxy mass and specific mass accretion and merger histories.

DISK GALAXIES WITH BROKEN LUMINOSITY PROFILES FROM COSMOLOGICAL SIMULATIONS

We present SPH cosmological simulations of the formation of three disk galaxies with a detailed treatment of chemical evolution and cooling. The resulting galaxies have properties compatible with observations: relatively high disk-to-total ratios, thin stellar disks and good agreement with the Tully-Fisher and the luminosity-size relations. They present a break in the luminosity profile at 3:0 0:5 disk scale lengths, while showing an exponential mass profile without any apparent breaks, in line with recent observational results. Since the stellar mass profile is exponential, only differences in the stellar populations can be the cause of the luminosity break. Although we find a cutoff for the star formation rate imposed by a density threshold in our star formation model, it does not coincide with the luminosity break and is located at 4:3 0:4 disk scale lengths, with star formation going on between both radii. The color profiles and the age profiles are “U-shaped”, with the minimum for both profiles located approximately at the break radius. The SFR to stellar mass ratio increases until the break, explaining the coincidence of the break with the minimum of the age profile. Beyond the break we find a steep decline in the gas density and, consequently, a decline in the SFR and redder colors. We show that most stars (64-78%) in the outer disk originate in the inner disk and afterwards migrate there. Such stellar migrations are likely the main origin of the U-shaped age profile and, therefore, of the luminosity break. Subject headings: galaxies: formation — galaxies: evolution — galaxies: spiral — galaxies: stellar content — methods: N-body simulations

Bright and dark matter in elliptical galaxies : mass and velocity distributions from self-consistent hydrodynamical simulations

We have analysed the mass and velocity distributions of two samples of relaxed elliptical-like objects (ELOs) identified, at z = 0, in a set of self-consistent hydrodynamical simulations operating in the context of a concordance cosmological model. ELOs have been identified as those virtual galaxies having a prominent, dynamically relaxed stellar spheroidal component, with no extended discs and very low gas content. Our analysis shows that they are embedded in extended, massive dark matter haloes, and they also have an extended corona of hot diffuse gas. Dark matter haloes have experienced adiabatic contraction along their assembly process. The relative ELO dark- to bright-mass content and space distributions show broken homology, and they are consistent with observational results on the dark matter fraction at the central regions, as well as on the gradients of the mass-to-light ratio profiles for boxy ellipticals, as a function of their stellar masses. These results indicate that massive ellipticals miss stars (i.e. baryons) at their central regions, as compared to less massive ones. Our simulations indicate that these missing baryons could be found beyond the virial radii as a hot, diffuse plasma. This mass homology breaking could have important implications to explain the physical origin of the Fundamental Plane relation. The projected stellar mass profiles of our virtual ellipticals can be well fitted by the Sersic formula, with shape parameters n that agree, once a stellar mass-to-light ratio independent of position is assumed, with those obtained from surface brightness profiles of ellipticals. The agreement includes the empirical correlations of n with size, luminosity and velocity dispersion. The total mass density profiles show a power-law behaviour over a large r/r vir interval, consistent with data on massive lens ellipticals at shorter radii. The velocity dispersion profiles show kinematical segregation, with no systematic mass dependence (i.e. no dynamical homology breaking) and a positive anisotropy (i.e. radial orbits), roughly independent of the radial distance outside the central regions. The line-of-sight (LOS) velocity dispersion profiles are declining. These results give, for the first time from cosmological simulations, a rather detailed insight into the intrinsic mass and velocity distributions of the dark, stellar and gaseous components of virtual ellipticals. The consistency with observations strongly suggests that they could also describe important intrinsic characteristics of real ellipticals, as well as some of their properties recently inferred from observational data (e.g. downsizing, the appearance of blue cores, the increase of the stellar mass contributed by the elliptical population as z decreases).

Adaptive Smooth Particle Hydrodynamics and Particle-Particle Coupled Codes: Energy and Entropy Conservation

We present and test a general-purpose code, called PPASPH, for evolving self-gravitating fluids in astrophysics, both with and without a collisionless component. In PPASPH, hydrodynamical properties are computed by using the SPH (Smoothed Particle Hydrodynamics) method while, unlike most previous implementations of SPH, gravitational forces are computed by a PP (Particle-Particle) approach. another important feature of this code is that hydrodynamics equations optionally include the correction terms appearing when

Scalar - tensor cosmological models

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grasil-3d: an implementation of dust effects in the SEDs of simulated galaxies

is not constant. Our code has been implemented by using the data parallel programming model on CM5(CM). PPASPH has been applied to study the importance of adaptative smoothing correction terms on the entropy conservation. We confirm Hernquists (1993) interpretation of the entropy violation observed in previous SPH simulations as a result of having neglected these terms. An improvement on the entropy conservation is not found by merely considering larger numbers of particles or different

The Lack of Structural and Dynamical Evolution of Elliptical Galaxies since z ~ 1.5: Clues from Self-Consistent Hydrodynamic Simulations

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Clues on the Physical Origin of the Fundamental Plane from Self-Consistent Hydrodynamical Simulations

choices. The correct continuum description is only obtained if the

Constraints on the scalar - tensor theories of gravitation from primordial nucleosynthesis

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