Integrated flux line ratio of the 3(0, 3)–2(0, 2) over 3(2, 1)–2(2, 0) transition of H₂CO. The synthesised beam for both lines and the ratio image is shown in the bottom left corner: 4.3′′ × 2.9′′, PA = –1.0°. The plus sign marks the position of the water maser reported by Lis et al. (1994) and the crosses mark (from north to south, respectively) the positions of the 1.3 cm sources VLA 4 and 5 from Rodríguez & Zapata (2013). The dashed grey contour shows the combined dust continuum emission at a level of 0.024 mJy beam^-1, the lowest black contour shown in Fig. 4.