Magnetic field log(B_ref/μG) vs. number density . The filled squares and crosses represent the number density region corresponding to the fitting of the lifetime of prestellar cores and Num_CORE as shown in Figs. 2 and 3 (see Tables B.1 and B.2). The dashed line is the least-squares fit. The vertical error bars correspond to magnetic field variations that yield a total factor of two (greater or lesser by a factor ) values of the growth time (lifetime).