On the filamentary environment of galaxies

The correlation between the large-scale distribution of galaxies and their spectroscopic properties at z= 1.5 is investigated using the Horizon MareNostrum cosmological run.We have extracted a large sample of 10⁵ galaxies from this large hydrodynamical simulation featuring standard galaxy formation physics. Spectral synthesis is applied to these single stellar populations to generate spectra and colours for all galaxies. We use the skeleton as a tracer of the cosmic web and study how our galaxy catalogue depends on the distance to the skeleton. We show that galaxies closer to the skeleton tend to be redder but that the effect is mostly due to the proximity of large haloes at the nodes of the skeleton, rather than the filaments themselves.This effect translates into a bimodality in the colour distribution of our sample. The origin of this bimodality is investigated and seems to follow from the ram pressure stripping of satellite galaxies within the more massive clusters of the simulation.The virtual catalogues (spectroscopical properties of the MareNostrum galaxies at various redshifts) are available online at http://www.iap.fr/users/pichon/MareNostrum/catalogues.