Cosmology

Abstract:

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 10^5 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 effects translate 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

Abstract:

MCG-6-30-15 is the archetypal example of a type I active galaxy showing broad 'red-wing' emission in its X-ray spectrum at energies below the 6.4 keV Fe Kα emission line and a continuum excess above 20 keV. Miller et al. showed that these spectral features could be caused by clumpy absorbing material, but Reynolds et al. have argued that the observed Fe Kα line luminosity is inconsistent with this explanation unless the global covering factor of the absorber(s) is very low. However, the Reynolds et al. calculation effectively considers the only source of opacity to be the Fe K bound-free transition and neglects the opacity at the line energy: correction to realistic opacity decreases the predicted line flux by a large factor. We also discuss the interpretation of the covering factor and the possible effect of occultation by the accretion disc. Finally, we consider a model for MCG-6-30-15 dominated by clumpy absorption, which is consistent with a global covering factor of 0.45, although models that include the effects of Compton scattering are required to reach a full understanding. Variations in covering fraction may dominate the observed X-ray spectral variability. © 2009 The Authors. Journal compilation © 2009 RAS.