An investigation of the B335 region through far infrared spectroscopy with ISO

We present far infrared spectra of the B335 dark cloud region, obtained with the Long Wavelength Spectrometer (LWS) on-board the ISO satellite. Deep spectra were obtained towards the far infrared outflow exciting source, located in the B335 core, and on the three associated Herbig Haro (HH) objects HH119 A, B and C. In addition, a region of about 9' in RA and 4' in Dec. was mapped which covers the whole molecular outflow. [CII]158 μm emission was found to be uniformly distributed across the observed region, with the intensity expected for a photodissociation region excited by the average interstellar field. The [OI]63 μm emission was detected only towards two out of the three HH objects and from the B335 FIR source; excitation from the high-velocity shocks responsible for the HH119 knots can account for the observed line intensity. CO line emission from the rotational levels J=15 to J=18 was detected only towards B335 FIR and can be modelled as arising in warm gas whose excitation temperature is in the range 150-800 K, located in a compact ( ~ 10-3 pc) and dense (nH2 ~ 106 cm-3 ) region. If we assume that the CO J = 6→5 line observed from the ground is also emitted from the same gas component, we derive for this component a temperature of 350 K and a density of 5•105 cm-3. Current collapse models for the B335 core fail to predict the presence of such warm gas in the infalling source envelope, at the spatial scales implied by our model fit. It is likely that the molecular emission is excited in a low-velocity (v ~ 10 km s-1 ) non-dissociative shock, originating at the base of the flow