A characterization of relatively hyperbolic groups via bounded cohomology

It was proved by Mineyev and Yaman that, if $(\Gamma, \Gamma')$ is a relatively hyperbolic pair, the comparison map $$H_b^k(\Gamma, \Gamma'; V) \to H^k(\Gamma, \Gamma'; V)$$ is surjective for every $k \ge 2$, and any bounded $\Gamma$--module $V$. By exploiting results of Groves and Manning, we give another proof of this result. Moreover, we prove the opposite implication under weaker hypotheses than the ones required by Mineyev and Yaman.