All Figures

	Figure 1: The Integral Shaped Filament (ISF) at the north end of the Orion A molecular cloud, observed in dust continuum emission at 850 microns. The grey-scale ranges from 0 to 5 Jys with a logarithmic stretch. The positions of the six sources located in the ISF are indicated by arrows pointing at the peak continuum flux locations. Details of the sources are found in Table 1.
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In the text

	Figure 2: The CO J=3-2 line profiles. Note the self-absorption in all sources except PDR1, and the extended line wings (dashed lines) in all sources except MMS6, and PDR1.
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In the text

	Figure 3: A selection of methanol lines observable with a single spectral setting, along with an SO line.
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In the text

	Figure 4: The HCN and HNC J=4-3 transitions.
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In the text

Figure 5: Determination of the equilibrium physical properties of molecular gas from formaldehyde line ratios. The top left panel presents the expected line ratio for the 303 - 202 and 322 - 221 transitions as functions of temperature and density (solid contours) against the expected line ratio for the 505 - 404 versus the 303 - 202 transitions (dashed contours). The remaining panels show the range of physical properties obtainable for the sources in the present study, with the solid lines denoting the 303 - 202 versus 322 - 221 ratio and the dashed lines providing the location of the 505 - 404 versus 303 - 202 ratio. Two sets of dashed lines are shown to account for possible beam dilution (see text). Also, the dotted lines provide an indication of the range of uncertainty on the calculations.

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In the text

Figure 6: Rotation diagrams for methanol. The input data are taken from the result of RADEX equilibrium calculations at a temperature of 100 K. a) Calculation with n = 107 cm-3..2 The slope of the data at high energies is significantly affected by the sub-thermal excitation, and the derived temperature from the rotation diagram does not correspond to the physical condition. The low energy lines are much closer to being thermalized, however, and the column density derived is close to the input column density of 1014 cm-3. b) Calculation with n = 108 cm-3. The slope of the data at high energies is still affected by the sub-thermal excitation, and the derived temperature from the rotation diagram continues to underestimate the physical condition. c) Calculation with n = 109 cm-3. At this density the rotation diagram produces a reasonable fit to the input physical conditions.

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In the text

Figure 7: Chi-squared confidence fits to the physical parameters of sources using the observed methanol lines and the radiative transfer code RADEX. The sources are (Top Left) FIR4 narrow component, (Top Center) FIR4 broad component, (Top Right) NGC 2071, (Bottom Left) MMS6, (Bottom Center) MMS9, (Bottom Right) PDR1. Note that there is often a strong degeneracy between the best fit temperature and density due to the lack of thermalization of the higher energy transitions.

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In the text

Figure 8: The range in abundances of the various molecular species investigated against T(H2CO). The abundances have been derived assuming a constant temperature and density envelope. Diamonds represent sub-millimeter sources, stars represent infrared sources, and the cross represents the PDR, with symbol size approximating the order unity uncertainty expected in the measurements. For all protostellar sources the CO abundance is depleted by about an order of magnitude. For all species the infrared sources show a remarkable similarity in abundances, however, in the case of methanol the very broad >10 km s-1 component from FIR4 has not been included. For most molecules the sub-millimeter sources have lower abundances while the PDR has the highest abundance.

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In the text