recover this inner component in more detail after subtracting the disc emission using a parametric model and we find that it is inconsistent with point source emission, it is significantly offset from the stellar position, and unlikely to be a background sub-millimetre galaxy.

The fact that the disc emission is consistent with being axisymmetric disfavours the scenario in which a planet is scattered out from the inner regions opening a gap through secular interactions with the disc [@Pearce2015doublering see their figure 6]. In their model, spiral density features are present in the planetesimal disc for hundreds of Myr, which should be imprinted in the mm-sized dust distribution as well, thus being detectable by our observations. In §\[sec:parmodel\] we fit parametric models to the data to study with more detail the level of axisymmetry of HD 107146’s disc. Moreover, in §\[sec:nbody\] we compare our observations with N-body simulations of a planet on a circular orbit clearing a gap in a planetesimal disc.

CO J=3-2 and HCN J=4-3 {#sec:gas}
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Despite the increasing number of CO gas detections in nearby debris discs [e.g. @Dent2014; @Moor2015gas; @Marino2016; @Marino2017etacorvi; @Lieman-Sifry2016; @Matra2017fomalhaut; @Moor2017], no CO v=0 J=3-2 emission is detected around HD 107146 in the 