¹⁴N/¹⁵N ratio map of HCN towards L1544. The map was computed only in the pixels where the integrated emission of both H¹³CN and HC¹⁵N was detected with a signal-to-noise ratio larger than 5. The IRAM 30 m beam of 30″ (∼5000 au) is shown in the bottom right of the map. The solid white contours are 30%, 60%, and 90% of the peak intensity of the N(H₂) map of L1544 computed from Herschel/SPIRE data (Spezzano et al. 2016). The column density of HCN was computed from the column density of H¹³CN assuming the ¹²C/¹³C ratio of 68 (Milam et al. 2005). The corresponding error is shown in Fig. A.3.