L1448-MM observations by the Herschel Key program, "Dust, Ice, and Gas
  In Time" (DIGIT)
  We present Herschel/PACS observations of L1448-MM, a Class 0 protostar with a
prominent outflow. Numerous emission lines are detected at 55 < lambda < 210
micrometer including CO, OH, H2O, and [O I]. We investigate the spatial
distribution of each transition to find that lines from low energy levels tend
to distribute along the outflow direction while lines from high energy levels
peak at the central spatial pixel. Spatial maps reveal that OH emission lines
are formed in a relatively small area, while [O I] emission is extended.
According to the rotational diagram analysis, the CO emission can be fitted by
two (warm and hot) temperature components. For H2O, the ortho-to-para ratio is
close to 3. The non-LTE LVG calculations suggest that CO and H2O lines could
instead be formed in a high kinetic temperature (T > 1000 K) environment,
indicative of a shock origin. For OH, IR-pumping processes play an important
role in the level population. The molecular emission in L1448-MM is better
explained with a C-shock model, but the atomic emission of PACS [O I] and
Spitzer/IRS [Si II] emission is not consistent with C-shocks, suggesting
multiple shocks in this region. Water is the major line coolant of L1448-MM in
the PACS wavelength range, and the best-fit LVG models predict that H2O and CO
emit (50-80)% of their line luminosity in the PACS wavelength range.
