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Index - ... - Simulations (1/3) - Simulations (2/3) - Simulations (3/3) - ...

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4.2 - Simulated XMM images of cosmic filaments

Filaments are a common feature of modern cosmological models and their existence is now a well observed feature of the galaxies mapped in redshift surveys. However, stars represent only a small fraction of the baryonic matter predicted by nucleosynthesis. Where is the rest? Simulations predict that most baryons are in moderately hot gas associated with filaments and groups (Cen and Ostriker 1999). If this is the case, then we have yet to observe a large fraction of the baryons in the universe.

In order to investigate their observability in the X-ray band, we have performed detailed N-body and hydrodynamic simulations. We selected two representative cosmological models: one dominated by a cosmological constant (and favored by current observations), and the other a flat, = 1 cosmology with a tilted spectrum of density perturbations. For both cosmologies, we focused our computational efforts on a filament about 30 h^-1 Mpc in length and used an adaptive mesh refinement (AMR) method to solve the equations of hydrodynamics. This new numerical technique (described in Bryan 1999) was used in order to achieve sufficient resolution (50 h^-1 kpc) in high-density regions and good shock-capturing behaviour in low density regions.

The results (for both CDM and tilted CDM models) are shown in Fig. 9-10 which demonstrate what an idealized X-ray image of this region would show. While the extremely diffuse gas of the filament is very difficult to observe, it's clear that the filamentary structure itself is well outlined by a chain of gas clumps with various masses and luminosities. In fact it is in this network of groups that a large fraction of the filament's baryons reside, and this work shows that a detection of that component is feasible. In Fig. 11-12 we include all instrumental effects and the background distribution of extragalactic objects (QSO). The groups embedded in the filament are visible. While it is more difficult to delineate the cluster outskirts, a cross-correlation with the optical survey, the weak-lensing results and the Sunyaev-Zel'dovich map will substantially enhance the strength of the signal. In this way, we may at last complete our inventory of the baryonic matter content of the universe.

tcdm_z0p5_10ks.ps.gz (gzipped Postscript, 22469 bytes)

lcdmrp_z0p5_10ksb.ps.gz (gzipped Postscript, 21794 bytes)

lcdmrp_z0p5_10ks_4as_qso.ps.gz (gzipped Postscript, 77073 bytes)

lcdmrp_z0p5_10ks_4as_qsof3.ps.gz (gzipped Postscript, 41046 bytes)

4.3 Towards new physics in the XMM group sample