2015A&A...578A..20M

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. 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. Herschel/PACS spectral maps are analyzed for six YSOs with bolometric luminosities of L_bol∼10²-10³L_☉. The maps cover spatial scales of ∼10⁴AU in several CO and H₂O lines located in the ∼55-210µm range. Rotational diagrams of CO show two temperature components at T_rot∼320K and T_rot~700-800K, comparable to low- and high-mass protostars probed at similar spatial scales. The diagrams for H₂O show a single component at T_rot∼130K, as seen in low-mass protostars, and about 100K lower than in high-mass protostars. Since the uncertainties in T_rot 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. Molecular excitation in intermediate-mass protostars is comparable to the central 10³AU of low-mass protostars and consistent within the uncertainties with the high-mass protostars probed at 3x10³AU scales, suggesting similar shock conditions in all those sources.