arXiv subjects

Bruno Guiderdoni

Publications and source records attributed to Bruno Guiderdoni.

23 records · Page 2Linked to original sources

arXiv2003

GALICS I: A hybrid N-body semi-analytic model of hierarchical galaxy formation

This is the first paper of a series that describes the methods and basic results of the GalICS model (for Galaxies In Cosmological Simulations). GalICS is a hybrid model for hierarchical galaxy formation studies, combining the outputs of large cosmological N-body simulations with simple, semi-analytic recipes to describe the fate of the baryons within dark matter halos. The simulations produce a detailed merging tree for the dark matter halos including complete knowledge of the statistical properties arising from the gravitational forces. We intend to predict the overall statistical properties of galaxies, with special emphasis on the panchromatic spectral energy distribution emitted by galaxies in the UV/optical and IR/submm wavelength ranges. In this paper, we outline the physically motivated assumptions and key free parameters that go into the model, comparing and contrasting with other parallel efforts. We specifically illustrate the success of the model in comparison to several datasets, showing how it is able to predict the galaxy disc sizes, colours, luminosity functions from the ultraviolet to far infrared, the Tully--Fisher and Faber--Jackson relations, and the fundamental plane in the local universe. We also identify certain areas where the model fails, or where the assumptions needed to succeed are at odds with observations, and pay special attention to understanding the effects of the finite resolution of the simulations on the predictions made. Other papers in this series will take advantage of different data sets available in the literature to extend the study of the limitations and predictive power of GalICS, with particular emphasis put on high-redshift galaxies.

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arXiv1999

Merging History Trees for Dark Matter Halos: Tests of the Merging Cell Model in a CDM Cosmology

The merging history of dark matter halos is computed with the Merging Cell Model proposed by Rodrigues & Thomas (1996). While originally discussed in the case of scale-free power spectra, it is developed and tested here in the framework of the cold dark matter cosmology. The halo mass function, the mass distribution of progenitors and child halos, as well as the probability distribution of formation times, have been computed and compared to the available analytic predictions. The halo auto-correlation function has also been obtained (a first for a semi-analytic merging tree), and tested against analytic formulae. An overall good agreement is found between results of the model, and the predictions derived from the Press & Schechter theory and its extensions. More severe discrepancies appear when formulae that better describe N-body simulations are used for comparison. In many instances, the model can be a useful tool for following the hierarchical growth of structures. In particular, it is suitable for addressing the issue of the formation and evolution of galaxy clusters, as well as the population of Lyman-break galaxies at high redshift, and their clustering properties.

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arXiv1999

Dark Matter Halos Merging Trees: the Merging Cell Model in a CDM Cosmology

We have constructed the merging history of dark matter halos in a SCDM cosmology, by means of a the {``Merging Cell Model''} (Rodrigues & Thomas 1996). It is based on the linear theory of growth of density fluctuations, and the Top-Hat model, and it takes into account mergers between halos through simplified criteria. The halo mass function, the progenitors and children mass distribution, the distribution of formation times, and the halo autocorrelation function (in the Lagrangian space of initial conditions) have been computed. To test the reliability of the model, results have been compared to the analytical predictions of the extended Press & Schechter theory, that in turn well describes results of N-body simulations. A general good agreement has been found, thus providing us with a reliable tool for rapidly addressing the issue of galaxy formation and evolution in hierarchical scenarios. The model is particularly suitable for studying galaxy clusters at low redshift, and the population of Lyman-break galaxies at high z.

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arXiv1999

Faint galaxies in semi--analytic models: how robust are the predictions?

In spite of their overall success, semi-analytic models of galaxy formation and evolution predict slopes of luminosity functions which are steeper than the observed ones. This discrepancy has generally been explained by subtle surface brightness effects acting on the observational samples. In this paper, we explicitly implement the computation of surface brightness in a simple semi-analytic model (with standard CDM), and we estimate the effect of observational surface brightness thresholds on the predicted luminosity functions. The crucial free parameter in this computation is the efficiency epsilon of supernova feedback which is responsible for the triggering of galactic winds. With the classical formalism for this process, it is difficult to reproduce simultaneously the Tully-Fisher relation and the flat slope of the observational luminosity function with the same value of epsilon. This suggests that the triggering of galactic winds is a complex phenomenon. [...] The conclusion of this heuristic paper is that a more realistic description of SN feedback is needed, and that surface brightness effects should not be neglected in the modelling of galaxy formation.

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arXiv1998

Contribution of Galaxies to the Background Hydrogen-Ionizing Flux

We estimate the evolution of the contribution of galaxies to the cosmic background flux at $912 Å$ by means of a semi-analytic model of galaxy formation and evolution. Such a modelling has been quite successful in reproducing the optical properties of galaxies. We assume hereafter the high-redshift damped Lyman-$α$ (DLA) systems to be the progenitors of present day galaxies, and we design a series of models which are consistent with the evolution of cosmic comoving emissivities in the available near infrared (NIR), optical, ultraviolet (UV), and far infrared (FIR) bands along with the evolution of the neutral hydrogen content and average metallicity of damped Lyman-$α$ systems (DLA). We use these models to compute the galactic contribution to the Lyman-limit emissivity and background flux for $0 \simeq z \le 4$. We take into account the absorption of Lyman-limit photons by HI and dust in the interstellar medium (ISM) of the galaxies. We find that the background Lyman-limit flux due to galaxies might dominate (or be comparable to) the contribution from quasars at almost all redshifts if the absorption by HI in the ISM is neglected. The ISM HI absorption results in a severe diminishing of this flux--by almost three orders of magnitude at high redshifts to between one and two orders at $z \simeq 0$. Though the resulting galaxy flux is completely negligible at high redshifts, it is comparable to the quasar flux at $z \simeq 0$.

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