Merger Rates of Dark-Matter Haloes

Understand

We derive analytic merger rates for dark-matter haloes within the framework of the Extended Press-Schechter (EPS) formalism.

• These rates become self-consistent within EPS once we realize that the typical merger in the limit of a small time-step involves more than two progenitors, contrary to the assumption of binary mergers adopted in earlier studies.
• We present a general method for computing merger rates that span the range of solutions permitted by the EPS conditional mass function, and focus on a specific solution that attempts to match the merger rates in N-body simulations.
• The corrected EPS merger rates are more accurate than the earlier estimates of Lacey & Cole, by ~20% for major mergers and by up to a factor of ~3 for minor mergers of mass ratio 1:10^4.