(a) Map (colour image) of the absolute value of the minimum (negative) brightness temperature of the N = 1-0, J =1/2-1/2, F=3/2-3/2 hyperfine component of the CN(1-0) line. (b) Map of the LSR velocity at which the minimum brightness shown in panel a is attained. The synthesised beam is shown in the bottom-right corner. The contour map represents the 3 mm continuum emission and is the same as in Fig. 1c.