Herschel-PACS legacy of low-mass protostars

Shocks are routinely invoked to reproduce some properties of the far-IR spectra, but standard models fail to reproduce the emission from key molecules, e.g., H_2_O. Here, we present the Herschel Photodetector Array Camera and Spectrometer (PACS) far-IR spectroscopy of 90 embedded low-mass protostars (Class 0/I).

The Herschel-PACS spectral maps, covering ~55-210{mu}m with a field of view of ~50", are used to quantify the gas excitation conditions and spatial extent using rotational transitions of H_2_O, high-J CO, and OH, as well as [OI] and [CII]. We confirm that a warm (~300K) CO reservoir is ubiquitous and that a hotter component (760+/-170K) is frequently detected around protostars. The line emission is extended beyond ~1000au spatial scales in 40/90 objects, typically in molecular tracers in Class 0 and atomic tracers in Class I objects.