2013ApJ...770..123G

We present 50-210 µm spectral scans of 30 Class 0/I protostellar sources, obtained with Herschel-PACS, and 0.5-1000 µm spectral energy distributions, as part of the Dust, Ice, and Gas in Time Key Program. Some sources exhibit up to 75 H₂ O lines ranging in excitation energy from 100 to 2000 K, 12 transitions of OH, and CO rotational lines ranging from J = 14 ⟶ 13 up to J = 40 ⟶ 39. [O I] is detected in all but one source in the entire sample; among the sources with detectable [O I] are two very low luminosity objects. The mean 63/145 µm [O I] flux ratio is 17.2±9.2. The [O I] 63 µm line correlates with L_bol, but not with the time-averaged outflow rate derived from low-J CO maps. [C II] emission is in general not local to the source. The sample L_bol increased by 1.25 (1.06) and T_bol decreased to 0.96 (0.96) of mean (median) values with the inclusion of the Herschel data. Most CO rotational diagrams are characterized by two optically thin components (<N> = 0.70± 1.12 x 10⁴⁹ total particles). N_CO correlates strongly with L_bol, but neither T_rot nor N_CO(warm)/N_CO(hot) correlates with L _bol, suggesting that the total excited gas is related to the current source luminosity, but that the excitation is primarily determined by the physics of the interaction (e.g., UV-heating/shocks). Rotational temperatures for H₂ O (<T_rot> = 194 ± 85 K) and OH (<T_rot> = 183 ±117 K) are generally lower than for CO, and much of the scatter in the observations about the best fit is attributed to differences in excitation conditions and optical depths among the detected lines.