dirty continuum-subtracted data cube. This non detection is, however, not surprising since HD 107146 is significantly older and fainter than the other systems in which primordial gas has been found (i.e. the hybrid discs). Furthermore, the sensitivity of these observations is expected to be insufficient to detect CO gas if being released through collisions of volatile-rich planetesimals [@Kral2017CO]. We search more carefully for CO emission by applying a matched filter technique [@Matra2015; @Marino2016; @Marino2017etacorvi; @Matra2017fomalhaut] in which we integrate the emission over an elliptic mask with the same orientation as the disc on the sky (see §\[sec:model\]), but in each spatial pixel we integrate only over those frequencies (i.e. radial velocities) where line emission is expected taking into account the Doppler shift due to Keplerian rotation. For this, we assume a stellar mass of 1 $M_{\sun}$, inclination of $19\degr$, PA of $153\degr$, and deprojected minimum and maximum radii of 40 and 150 au, respectively. Using this method we obtain an integrated line flux $3\sigma$ upper limit of 74 mJy km s$^{-1}$. Note that we consider the two possible directions of the rotation, obtaining similar limits. We also search for emission that could be present at a specific radius by integrating 