Perfect Matchings in Random Subgraphs of Regular Bipartite Graphs

Consider the random process in which the edges of a graph $G$ are added one by one in a random order. A classical result states that if $G$ is the complete graph $K_{2n}$ or the complete bipartite graph $K_{n,n}$, then typically a perfect matching appears at the moment at which the last isolated vertex disappears. We extend this result to arbitrary $k$-regular bipartite graphs $G$ on $2n$ vertices for all $k=\Omega(n)$. Our proof relies on a new result regarding the structure of dense, bipartite, regular graphs which may be of independent interest. For smaller values of $k$, we construct bipartite $k$-regular graphs in which the last isolated vertex disappears long before a perfect matching appears.