The outflow from the class 0 protostar HH 25MMS: methanol enhancement in a well-collimated flow

We present millimetre and submillimetre observations of HH 25MMS made with the James Clerk Maxwell Telescope (JCMT). From greybody fits to the continuum data we can confirm that HH 25MMS is a class 0 source, with a bolometric luminosity of similar to 6 L. and T-bol = 34 +/- 2 K. The ratio of submillimetre-to-bolometric luminosity is similar to 0.05, mon than 10 times higher than the defining value specified by Andre, Ward-Thompson & Barsony. The radio continuum source lies at the centre of a highly collimated, jet-driven, bipolar molecular outflow which lies close to the plane of the sky. We have mapped the southern lobe in the emission of CO J = 3-->2 and find that the CO peaks upstream of the bright H-2 knot HH25C, indicative of a prompt entrainment mechanism. A plot of the momentum per unit distance along the outflow axis confirms this. Furthermore, the jet shows evidence of a time-varying direction. The southern lobe is the site of significant methanol enhancement. Maps are presented of the J(K) = 5(K)-->4(K) group of lines which show emission solely within the confines of the southern outflow lobe. HH 25MMS is thus only the second class 0 source to have the distribution of methanol mapped within its outflow. Eight further methanol lines have been observed at the position of one of the H-2 knots (HH25C) to constrain better an estimate of the methanol column density and excitation temperature. The methanol at this position is slightly warmer than the ambient gas with an excitation temperature of 22-34 K, and the abundance of methanol is enhanced by a factor of at least 200 over that in the ambient gas. Statisitical equilibrium calculations confirm this, although the results are not particularly well constrained. The gas kinetic temperature is somewhat higher than the excitation temperature at similar to 60 K, the H-2 number density lies within a factor of 5 of 10(5) cm(-3), and the abundance is within a factor of 10 of 2.6 x 10(-7) relative to H-2. The SO J(N) = 8(7)-->7(6) and SiO J = 7-->6 lines are also observed within the outflow, emission from the latter being predominantly redshifted relative to the rest velocity.