Far-infrared CO and H

Context. Intermediate-mass young stellar objects (YSOs) provide a link to understanding how feedback from shocks and UV radiation scales from low- to high-mass star forming regions. Aims. Our aim is to analyze excitation of CO and H2O in deeply embedded intermediate-mass YSOs and compare it with similar studies on low-mass and high-mass YSOs. Methods. Herschel/PACS spectral maps are analyzed for six YSOs with bolometric luminosities of Lbol ~ 102−103L⊙. The maps cover spatial scales of ~104 AU in several CO and H2O lines located in the ~55–210 μm range. Results. Rotational diagrams of CO show two temperature components at Trot ~ 320 K and Trot ~ 700–800 K, comparable to low- and high-mass protostars probed at similar spatial scales. The diagrams for H2O show a single component at Trot ~ 130 K, as seen in low-mass protostars, and about 100 K lower than in high-mass protostars. Since the uncertainties in Trot are on the same order as the difference between the intermediate and high-mass protostars, we cannot conclude whether the change in rotational temperature occurs at a specific luminosity or whether the change is more gradual from low- to high-mass YSOs. Conclusions. Molecular excitation in intermediate-mass protostars is comparable to the central 103 AU of low-mass protostars and consistent within the uncertainties with the high-mass protostars probed at 3 × 103 AU scales, suggesting similar shock conditions in all those sources