On the commutative quotient of Fomin-Kirillov algebras

The Fomin-Kirillov algebra ${\mathcal{E}}_n$ is a noncommutative algebra with a generator for each edge in the complete graph on $n$ vertices. For any graph $G$ on $n$ vertices, let ${\mathcal{E}}_G$ be the subalgebra of ${\mathcal{E}}_n$ generated by the edges in $G$. We show that the commutative quotient of ${\mathcal{E}}_G$ is isomorphic to the Orlik-Terao algebra of $G$. As a consequence, the Hilbert series of this quotient is given by $(-t)^n \chi_G(-t^{-1})$,where$\chi_G$isthechromaticpolynomialof$G$. We also give a reduction algorithm for the graded components of ${\mathcal{E}}_G$ that do not vanish in the commutative quotient and show that their structure is described by the combinatorics of noncrossing forests.