# Global Collapses and Expansions in Star-Forming Clouds

## TL;DR

This paper presents a hydrodynamic model for star-forming clouds that explains red asymmetric molecular line profiles as a result of envelope expansion with core collapse, supported by spectral line simulations.

## Contribution

It introduces a self-similar EECC hydrodynamic model framework to interpret red asymmetric line profiles in star-forming clouds, linking observations to core expansion and collapse dynamics.

## Key findings

- Red asymmetric line profiles indicate envelope expansion with core collapse.
- EECC models can reproduce observed spectral line asymmetries.
- Hydrodynamic processes are crucial in star formation signatures.

## Abstract

Spectral molecular line profile observations of star-forming molecular clouds sometimes show distinct red asymmetric double-peaked molecular line profiles with weaker blue peaks and stronger red peaks. For some star-forming molecular clouds, such molecular transitions with red asymmetric line profiles and blue asymmetric line profiles (i.e. blue asymmetric double-peaked molecular line profiles with weaker red peaks and stronger blue peaks) may coexist in spatially resolved spectral observations, while for others, such molecular transitions with red asymmetric line profiles may completely dominate in spatially resolved spectral observations. Blue asymmetric line profiles are usually interpreted as signals of central core collapses, while red asymmetric line profiles remain unexplained. In this paper, we advance a spherically symmetric self-similar hydrodynamic model framework for envelope expansions with core collapses (EECC) of a general polytropic molecular gas cloud under self-gravity. Based on such EECC hydrodynamic cloud models, we perform tracer molecular line profile calculations using the publicly available RATRAN code for star-forming clouds with spectroscopic signatures of red asymmetric line profiles. The presence of red asymmetric line profiles from molecular cloud cores indicates that EECC processes are most likely an essential hydrodynamic process of star formation. With spatial distributions, we explore various profiles of molecular lines for several tracer molecules in different settings of EECC dynamic models with and without shocks.