Inflows in massive star formation regions

TL;DR

This paper reviews recent observational evidence of inflow motions in massive star formation regions, discussing how these findings support accretion models over merger models and highlighting the need for further detailed studies.

Contribution

It synthesizes recent observational data on inflow motions, compares theoretical models, and emphasizes the importance of high-resolution observations with ALMA for understanding massive star formation.

Findings

Inflow signatures are more common in developed radiation pressure regions.

Interferometer studies show more pronounced blue profiles and inverse P Cygni profiles.

Observations tend to support the accretion model over merger models.

Abstract

How high-mass stars form remains unclear currently. Calculation suggests that the radiation pressure of a forming star can halt spherical infall, preventing its further growth when it reaches 10 M$_{\odot}$. Two major theoretical models on the further growth of stellar mass were proposed. One model suggests the mergence of less massive stellar objects, and the other is still through accretion but with the help of disk. Inflow motions are the key evidence of how forming stars further gain mass to build up massive stars. Recent development in technology has boosted the search of inflow motion. A number of high-mass collapse candidates were obtained with single dish observations, mostly showed blue profile. The infalling signatures seem to be more common in regions with developed radiation pressure than in younger cores, which opposes the theoretical prediction and is also very different from that of low mass star formation. Interferometer studies so far confirm such tendency with more obvious blue profile or inverse P Cygni profile. Results seem to favor the accretion model. However, the evolution tendency of the infall motion in massive star forming cores needs to be further explored. Direct evidence for monolithic or competitive collapse processes is still lack. ALMA will enable us to probe more detail of gravity process.