9. Critical universe
We now consider the case of a critical universe with a CDM power-spectrum (Davis et al.1985) normalized to . We also choose and km s-1 Mpc- 1. Thus, as in the previous case of an open universe our model is consistent with the studies described in VS II and Valageas et al. (1999a).
9.1. Quasar luminosity function
We first present our results for the redshift evolution of the quasar luminosity function in Fig. 18.
We can check that our results are similar to those obtained previously for an open universe and they again agree reasonably with observations. This is not very surprising since we use the same physical model so that we recover a similar behaviour. We present in Fig. 19 the quasar number counts we obtain from our model.
We can see that our results are similar to those displayed previously in Fig. 2 and that our predictions are still marginally consistent with the lack of observation in the HDF.
We present in Fig. 20 the redshift evolution of the IGM temperature , the virial temperature of the smallest objects which can cool at a given time, and the mass averaged temperature .
We can see that our results are again very close to those obtained for an open universe. Indeed, the structure formation process is quite similar and it must agree with the same observations (quasar and galaxy luminosity functions, Lyman- column density distribution) at low z.
We display in Fig. 21 the redshift evolution of the background radiation and the comoving star formation rate.
We can check that we recover the behaviour obtained previously for an open universe. However, the reionization redshift is smaller than previously. This is related to the lower normalization of the power-spectrum as compared to the previous case. This leads to fewer bright quasars at high z (compare Fig. 18 and Fig. 1) and to a smaller radiative output.
We can also check that the hydrogen and helium reionization process is close to our previous results (as for the reheating). Thus, for most practical purposes both critical and open cosmologies allow reasonable reheating and reionization histories which are very similar. In fact, the uncertainties involved in the galaxy and quasar formation processes are probably too large to favour significantly one of these two possible scenarios (as compared to the other). However, both models are consistent with present observations.
© European Southern Observatory (ESO) 1999
Online publication: June 18, 1999