Forming Protostars in Molecular Clouds with Shocked Envelope Expansion and Core Collapse

TL;DR

This paper presents observational evidence and modeling of envelope expansion with core collapse (EECC) in star-forming molecular clouds, revealing a self-similar shock phase through molecular line profiles and continuum emissions.

Contribution

It demonstrates that red profiles in molecular lines can be explained by EECC, providing a new interpretation for global cloud dynamics in star formation.

Findings

Red profiles indicate envelope expansion with core collapse.

Spectral profiles fit well with the EECC hydrodynamic shock model.

Predictions for future observations of molecular lines and continuum emissions.

Abstract

Spectral observations of molecular line profiles reveal the so-called `blue profiles' for double-peaked molecular lines with stronger blue and weaker red peaks as notable features for star-forming cloud core collapses under the self-gravity. In contrast, 25-30 per cent of observed molecular spectral line profiles in star-forming clouds or cores also show the so-called double-peaked `red profiles' with red peaks stronger than blue peaks. Gao & Lou (2010) show that these unexplained `red profiles' can be signatures of global dynamics for envelope expansion with core collapse (EECC) within star-forming molecular clouds or cores. We demonstrate here that spatially-resolved `red profiles' of HCO+ (J=1-0) and CS (J=2-1) molecular transitions from the low-mass star-forming cloud core FeSt 1-457 together with its radial profile of column density inferred from dust extinction observations appear to reveal a self-similar hydrodynamic shock phase for global EECC. Observed spectral profiles of C18O (J=1-0) are also fitted by the same EECC model. For further observational tests, the spatially-resolved profiles of molecular transitions HCO+ (J=3-2) and CS (J=3-2) as well as the radial profiles of (sub)millimetre continuum emissions at three wavelengths of 1.2mm, 0.85mm and 0.45mm from FeSt 1-457 are also predicted.