SIMBAD references

We compare the observed merger rate of galaxies over cosmic time and the frequency of collisional ring galaxies (CRGs), with analytic models and halo merger and collision rates from a large cosmological simulation. In the Λ cold dark matter (ΛCDM) model, we find that the cosmic merger fraction does not evolve strongly between 0.2 ≤ z ≤ 2, implying that the observed decrease in the cosmic star formation rate since z ∼ 1 might not be tied to a disappearing population of major mergers. Haloes hosting massive galaxies undergo on average ∼2 mergers from z ≤ 2 up to present day, reflecting the late assembly time for the massive systems and the related down-sizing problem. The cosmic merger rate declines with redshift: at the present time, it is of a factor of 10 lower than at z ∼ 2 in reasonable agreement with the current available data. The rate of CRG formation derived from the interactions between halo progenitors up to z = 2 is found to be a good tracer of the cosmic merger rate. In the ΛCDM model, the rate of CRGs as well as the merger rate do not scale as (1 + z)^m as suggested by previous models. Our predictions of cosmic merger and CRG rates may be applied to forthcoming surveys such as GOODS and zCOSMOS.