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Mar 2009
  • CINES received a 150 TFlops machine
  • GENCI has acquired for the French University Supercomputing Center a 12288 core SGI Altix. It is ranked 14th in the World and first in France.
  • Site Web du CINES
  • IDRIS received a 140 Tflops BlueGene/P machine.
  • The CNRS supercomputing centre has acquired a new BlueGene machine with 40480 processors and 20 To of RAM memory.
  • See the press release.
  • Mare Nostrum simulation down to z=1.55
  • We carried out our fourth run of MareNostrum down to z=1.55 while producing 150 Million "stars". More info is given here
  • Horizon 4Pi 4096^3 down to z=0
  • We have carried a full sky 2Gpc/h 4096^3 Dark Matter simulation down to z=0. More details can be found here
  • Horizon 4Pi run 2048^3 completed
  • We have completed a full sky cone run of DM with RAMSES on platine CEA with 2048^3 particles. See a slice here
  • Mare Nostrum @ z=1.9
  • We carried out our third run of MareNostrum down to z=1.9 while producing 120 Million "stars"
  • Mare Nostrum simulation down to z=2.4
  • We carried our second run on the Mare Nostrum supercomputing center down to z=2.4, thanks to 4-fold improvement in overall performance.
  • 1024^3 500 h-1Mpc simulation completed
  • RAMSES run of the HORIZON initial condition was carried down to z=0 using 1024^3 dark matter particles in a (500 Mpc/h)^3 box with up to 16 levels of refinement (corresponding to local effective resolution of 65536).
  • Horizon 1024^3 100 Mpc/h simulation completed.
  • A RAMSES run of the HORIZON initial condition was carried down to z=0 using 1024^3 dark matter particles in a (100 Mpc/h)^3 box with up to 16 levels of refinement (corresponding to local effective resolution of 65536).
  • A 43 Tflops supercomputer at CEA
  • CCRT, the supercomputing centre of CEA, has just received a new BULL supercomputer with 6800 processors and 13.6 Tb of RAM memory. This facility is dedicated to academic and industrial research.
  • Lire le communiqué
  • Fourth Horizon Workshop 2006b
  • The 4th workshop takes place from December, the 11th to December, the 12th at Paris Observatory. Registration form available here.
  • MareNostrum simulation has started at BSC
  • After 1 week of operations, we have reached redshift 4. The simulation will proceed further more during the next quarters. We have started to post-process these initial data.
  • Horizon Grid
  • The Horizon grid is now in operation. It links the 6 quadri opteron of Meudon, Paris, Lyon, Saclay, IAP and Marseille and is open to all members of the collaboration. Voir ce lien
  • Third Horizon Workshop 2006a
  • Horizon Workshop 2006a 10, 11 and 12 april 2006 in Lyon. It will be dedicated to progress reports. Registration form
  • Horizon is part of the DEISA "Extreme Computing Initiative"
  • Horizon will launch one extreme application for galaxy formation using the DEISA infrastructure at Mare Nostrum
  • DEISA web site
  • Second Horizon Workshop
  • Horizon Workshop 2005 took place at Paris Observatory the 14th and 15th november. It was dedicated to internal discussions and management issues.
  • November 2005: Horizon méso-machine is fully operational at HPC1
  • October 2005: Horizon was awarded a 500 k€ grant by ANR, the French Science Foundation.
  • Horizon response to «ANR Blanche» Call for Proposals has been succesfull in the «UNIVERS» program.
  • ANR web site
  • July 2005: HP France was selected to host the Horizon "meso-computer"
  • HP company has succesfully answered the "call for proposals" issued by the Hrizon Project for a medium-size dedicated super-computer. The computer will be hosted at HPC1, the HP high performance computing center near Paris.
  • February 2005: INSU and CEA agree to fund the Horizon "meso-machine".
  • Horizon has submitted to INSU a proposal for funding a medium-size computer dedicated to the project. The proposal was accepted as a joint CEA and INSU operation.
  • September 2004: Kick-off meeting in Paris
  • During 3 days (13, 14 and 15 of september), 30 scientists have met at Observatoire de Paris to set up the basic organisation and objectives of the Horizon Project.
  • KO Meeting
  • June 2004: Project report at SF2A in Paris
  • April 2004: Horizon received official support from ASSNA.
  • The french initiative «Action Spécifique pour les Simulations Numériques en Astrophysique» have given to the Horizon project its "label" for outstanding and structuring computational project.
  • April 2004: The french Astroparticule program provides financial support for the Horizon "mini-grid"
  • The Programme Astro-Particule, a joint IN2P3 and INSU initiative, has agreed to finance 6 quad AMD64 servers dedicated to the Horizon Project.
  • January 2004: Review by PNC and PNG
  • Both PNG and PNC scientific comitees are officially supporting the Horizon Project initiative.
  • June 2003: Presentation of the project to SF2A
  • Theoretical Virtual Observatory workshop (IAP April 5-6, 2006)
  • A workshop dedicated to the Theoretical Virtual Observatory will take place at IAP on April 5-6th.

    The goal is to bring together experts of the Virtual Observatory and theoreticians who would like to make results of their simulations (e.g. databases or catalogs) or numerical codes available to the worldwild astronomical community.

  • Program and speakers


A mock galaxy catalog from cosmological simulations

by Guiderdoni Bruno (Thursday 10 January 2008)

The current version of the GALICS catalog is available at

Researchers who are involved in observational programs, and who are willing to get mock catalogs that are customized to their needs should contact the author of this article.

A brief introduction to the simple modelling of hierarchical galaxy formation

In the early 1990’s, several authors proposed attempts to model galaxy formation in a cosmological context, from initial density fluctuations to the observed features of galaxies. These attempts were made possible by a slow but steady progress in the undertanding of the role of (cold) dark matter, and of the processes that rule the physics of baryons. In these early papers, previous works were linked together to produce a consistent scenario, with some variants, that was able to predict a lot of properties, and to be tested against observations.

The implementation of this scenario was made possible through semi-analytic calculations that can be run quite easily on a computer. It starts from the modelling of the power spectrum of (dark matter) density fluctuations at some given age after recombination. Then the properties of dark matter halos are easily computed from two numbers: the (linearly extrapolated to z=0) density contrast and the halo mass. More specifically, the collapse redshift, the virial radius, the circular velocity, and the density profile after collapse can be computed. The Press-Schecher formalism gives the number density of halos of mass M at a collapse redshift z, as well as (in its extended form) the probabilty density that matter elements that are in a given halo at a given redshift can be incorporated in a more massive halos at a lower redshift. All this is sufficient to draw Monte-Carlo realizations of this process, and to construct merging history trees of dark matter halos, with all their properties.

Of course, these merging history trees of dark matter halos, and the properties of the latter can be measured on large simulations of cosmological volumes. In any case, it is necessary to get this description of the history of the halos as a first step.

Then the description of the baryons can be modelled. Simple, but physically motivated recipes are introduced to model the following processes: gas heating during the collapse of dark matter halos (and possibly after heating by radiations), gas cooling in the potential wells of dark matter halos, conservation of angular momentum, rotational or pressure equilibrium, star formation, stellar evolution, stellar feedback (energy, gas, and heavy elements) to the interstellar and/or intergalactic medium, interaction between galaxies, gas stripping, major and minor merging of galaxies and the formation of spheroids.

This gives the merging history tree of galaxies within the merging history tree of dark matter halos.

Once the star formation rate and metal content histories of each galaxy is computed along its merging history tree, the multiwavelength spectrophotometric properties can be derived. A quick estimate of the dust content of each galaxy (based on its gas metallicity) and simple transfer can be added in order to compute (UV-optical) extinction and (IR-submm) emission.

At the end of the computation, the statistical distribution of quantities such as galaxy masses, gas contents, luminosities, radii, morphologies, etc. can be predicted at any time/redshift.