Street, MS-108, Houston, Texas 77005, USA\
    $^{9}$Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK\
    $^{10}$Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA\
    $^{11}$Department of Physics and Astronomy, California State University Northridge, 18111 Nordhoff Street, Northridge, CA 91130, USA\
    $^{12}$National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475, USA\
bibliography:
- 'SM\_pformation.bib'
date: 'Accepted XXX. Received YYY; in original form ZZZ'
title: A gap in the planetesimal disc around HD 107146 and asymmetric warm dust emission revealed by ALMA
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circumstellar matter - planetary systems - planets and satellites: dynamical evolution and stability - techniques: interferometric - methods: numerical - stars: individual: HD 107146.

Introduction {#sec:intro}
============

While exoplanet campaigns have discovered thousands of close in planets in the last decade, at separations greater than 10 au it has only been possible to detect a few gas giants, mainly through direct imaging [^2] [@Marois2008; @Lagrange2009betapicb; @Rameau2013]. Protoplanetary disc observations, on the other hand, have shown that enough mass in both dust and gas to form massive planets resides at large stellocentric distances [see review by @Andrews2015]. In addition, the detection of cold dusty debris discs at tens of au shows that 