A compactification of the moduli space of self-maps of ${\mathbb{C}\mathbb{P}}^1$ using stable maps

We present a new compactification $M(d,n)$ of the moduli space of self-maps of ${\mathbb{C}\mathbb{P}}^1$ of degree $d$ with $n$ markings. It is constructed via GIT from the stable maps moduli space $\ ar M_{0,n}($\mathbb{C}\mathbb{P}$^1 \times $\mathbb{C}\mathbb{P}$^1, (1,d))$. We show that it is the coarse moduli space of a smooth Deligne-Mumford stack and we compute its rational Picard group. Using the recursive boundary structure inherited from the stable maps space, we give an explicit algorithm for computing top-intersection numbers of divisors on $M(d,n)$. We also study the $m$-fold iteration map $M(d,n) \dashrightarrow M(d^m,n)$ and we give a geometric way to extend this rational map to parts of the boundary of $M(d,n)$.