Published online by Cambridge University Press: 17 December 2021
Using the theory of 
${\mathbf {FS}} {^\mathrm {op}}$ modules, we study the asymptotic behavior of the homology of 
${\overline {\mathcal {M}}_{g,n}}$, the Deligne–Mumford compactification of the moduli space of curves, for 
$n\gg 0$. An 
${\mathbf {FS}} {^\mathrm {op}}$ module is a contravariant functor from the category of finite sets and surjections to vector spaces. Via copies that glue on marked projective lines, we give the homology of 
${\overline {\mathcal {M}}_{g,n}}$ the structure of an 
${\mathbf {FS}} {^\mathrm {op}}$ module and bound its degree of generation. As a consequence, we prove that the generating function 
$\sum _{n} \dim (H_i({\overline {\mathcal {M}}_{g,n}})) t^n$ is rational, and its denominator has roots in the set 
$\{1, 1/2, \ldots, 1/p(g,i)\},$ where 
$p(g,i)$ is a polynomial of order 
$O(g^2 i^2)$. We also obtain restrictions on the decomposition of the homology of 
${\overline {\mathcal {M}}_{g,n}}$ into irreducible 
$\mathbf {S}_n$ representations.
The author is partially supported by NSF-Grant No. DMS-1903040.