Mass spectrum of fragments identified in our ¹³CO(J = 2–1) observations (solid line). Following the prescription of Maíz Apellániz & Úbeda (2005) to minimize errors in histograms with a small number of objects, we set bin widths so that each bin includes approximately the same number of objects (six or seven). The dashed line shows the mass spectrum calculated from the PAGI dispersion relation (see Eq. (12)) for Σ = 9 × 10^-4 g cm^-2, T = 15 K and P_EXT = 1.4 × 10^-12 dyne cm^-2 (parameters determined in Sect. 5.4). Dash-dotted and dotted lines show power law with slopes −1.7 and −2.35, respectively.