Far infrared mapping of the gas cooling along the L1448 outflow

The molecular outflows associated with the two Class 0 sources L1448-mm and L1448-IRS3 have been mapped with the spectrometers on board the ISO satell ite allowing to study in detail the physical and chemical structure of the shocked gas. The far infrared cooling is mainly due to the emission from pu re rotational lines of CO, H2O and Ha excited at temperatures between 500 a nd 1200 K. [O I]63 mu m emission is also widespreadly observed along the fl ows. Additional ground based observations of the (CO)-C-12 4-3 and 3-2 tran sitions in the surroundings of the L1448-mm source allow us to localize thi s warm emission in the extreme high velocity clumps forming the collimated molecular jet responsible for the entrainment of the outflow. Our analysis shows therefore that this jet is hotter than previously thought on the basi s of millimeter observations alone. A comparison with existing models suggests that the excitation along the ou tflow from L1448-mm is mainly due to low velocity (V-s less than or equal t o 20km s(-1)) non-dissociative shocks (C-shocks) probably developed as the jet proceeds through a medium already put into motion by previous episodes of mass loss. Excitation from turbulent mixing layers along the molecular j et axis seems not able to explain the observed cooling ratios among the dif ferent molecular components. An higher excitation shock component is likely present in the direction of the source L1448-IRS3, as testified by the: detection of the [Si II] 35 mu m line and by a larger contribution of the [O I] emission. Finally the abundance of gas-phase H2O is largely enhanced with respect to its interstellar value all along the flow. Both the total luminosity of wat er and its abundance correlate with SiO at high excitation, implying that b oth H2O and SiO are released in the low-velocity shocks developed along the outflow.