In our paper here, Himes, Miller, Nariman, and myself prove that Hatcher-Vogtmann’s conjecture is false, at least for $n=5$. It is also probably false for larger $n$, but our ignorance of the unstable cohomology of $Aut(F_n)$ prevents us from proving this via our techniques. I do not know any reasonable conjecture as to what the dualizing module is.

In our paper here, Himes, Miller, Nariman, and myself prove that Hatcher-Vogtmann’s question has a negative answer, at least for $n=5$. It also probably has a negative answer for larger $n$, but our ignorance of the unstable cohomology of $Aut(F_n)$ prevents us from proving this via our techniques. I do not know any reasonable conjecture as to what the dualizing module is.