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arXiv · 1802.03379

The Herschel-PACS legacy of low-mass protostars: Properties of warm and hot gas and its origin in far-UV illuminated shocks

Agata Karska·Michael J. Kaufman·Lars E. Kristensen·Ewine F. van Dishoeck·Gregory J. Herczeg·Joseph C. Mottram·Łukasz Tychoniec·Johan E. Lindberg·Neal J. Evans II·Joel D. Green·Yao-Lun Yang·Antoine Gusdorf·Dominika Itrich·Natasza Siódmiak
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Abstract

Recent observations from Herschel allow the identification of important mechanisms responsible for the heating of gas surrounding low-mass protostars and its subsequent cooling in the far-infrared (FIR). 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-PACS far-IR spectroscopy of 90 embedded low-mass protostars (Class 0/I). The Herschel-PACS spectral maps covering $\sim55-210$ $\mu$m with a field-of-view of $\sim$50'' are used to quantify the gas excitation conditions and spatial extent using rotational transitions of H$_{2}$O, high-$J$ CO, and OH, as well as [O I] and [C II]. We confirm that a warm ($\sim$300 K) CO reservoir is ubiquitous and that a hotter component ($760\pm170$ K) is frequently detected around protostars. The line emission is extended beyond $\sim$1000 AU spatial scales in 40/90 objects, typically in molecular tracers in Class 0 and atomic tracers in Class I objects. High-velocity emission ($\gtrsim90$ km s$^{-1}$) is detected in only 10 sources in the [O I] line, suggesting that the bulk of [O I] arises from gas that is moving slower than typical jets. Line flux ratios show an excellent agreement with models of $C$-shocks illuminated by UV photons for pre-shock densities of $\sim$$10^5$ cm$^{-3}$ and UV fields 0.1-10 times the interstellar value. The far-IR molecular and atomic lines are a unique diagnostic of feedback from UV emission and shocks in envelopes of deeply embedded protostars.

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Agata Karska, Michael J. Kaufman, Lars E. Kristensen, Ewine F. van Dishoeck, Gregory J. Herczeg, Joseph C. Mottram, Łukasz Tychoniec, Johan E. Lindberg, Neal J. Evans II, Joel D. Green, Yao-Lun Yang, Antoine Gusdorf, Dominika Itrich, Natasza Siódmiak. 2018-02-09. The Herschel-PACS legacy of low-mass protostars: Properties of warm and hot gas and its origin in far-UV illuminated shocks. https://doi.org/10.3847/1538-4365/aaaec5

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