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

Abstract

This is the first paper of a series that describes the methods and basic results of the GALICS model (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 haloes. The simulations produce a detailed merging tree for the dark matter haloes, 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 ultraviolet/optical and infrared/submillimetre 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 with several data sets, 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.

Building merger trees from cosmologicalN-body simulations

“…Both methods are then run on the same N-body simulation described in paper GalICS I (Hatton et al 2003). This simulation contains 256 3 particles of 8.03 × 10 9 M enclosed in a volume of 150 comoving Mpc on a side, with periodic boundary conditions.…”

“…The further complication with respect to the detection of subhaloes previously discussed is that this mass assembly is a dynamical and continuous process, which is only captured by a finite number of discrete time outputs (typically 50 between redshifts 20 and 0, see e.g. Hatton et al 2003) of an N-body simulation. This means that time resolution issues superimpose on mass resolution issues that were our sole limitation up to now.…”

Galaxy formation in the Planck cosmology – I. Matching the observed evolution of star formation rates, colours and stellar masses

“…Semi-analytic modelling is a particular simulation method which is optimized to connect the observed properties of the galaxy population -abundances, scaling relations, clustering and their evolution with redshift -to the astrophysical processes that drive the formation and evolution of individual galaxies (e.g. White 1989;Cole 1991;Lacey & Silk 1991;White & Frenk 1991;Cole et al 1994;Somerville & Primack 1999;Hatton et al 2003;Kang et al 2005;Lu et al 2011;Benson 2012). Simple phenomenological descriptions of the relevant processes are needed, each typically involving uncertain efficiency and scaling parameters.…”

The new semi-analytic code GalICS 2.0 – reproducing the galaxy stellar mass function and the Tully–Fisher relation simultaneously

“…GalICS 2.0 builds on our previous experience with Gal-ICS (Hatton et al 2003;Cattaneo et al 2006Cattaneo et al , 2008Cattaneo et al , 2013 but is more than a new version. The entire code has been re-written from scratch.…”