# A survey of molecular cores in M17 SWex

## TL;DR

This survey of molecular cores in M17 SWex reveals that magnetic fields likely prevent core collapse, explaining the region's low massive star formation despite the presence of massive cores.

## Contribution

It provides the first detailed analysis of core stability and magnetic influence in M17 SWex using N2H+ data and compares core properties with star formation activity.

## Key findings

- Most cores are gravitationally stable with external pressure.
- Four massive cores contain YSOs but show no active massive star formation.
- Strong magnetic fields may inhibit core collapse and star formation.

## Abstract

A survey of molecular cores covering the infrared dark cloud known as the M17 southwest extension (M17 SWex) has been carried out with the 45 m Nobeyama Radio Telescope. Based on the N2H+ (J= 1-0) data obtained, we have identified 46 individual cores whose masses are in the range 43 to 3026 Mo. We examined the relationship between the physical parameters of the cores and those of young stellar objects (YSOs) associated with the cores found in the literature. The comparison of the virial mass and the core mass indicates that most of the cores can be gravitationally stable if we assume a large external pressure. Among the 46 cores, we found four massive cores with YSOs. They have large mass of >~ 1000Mo and line width of >~ 2.5 km s^-1 which are similar to those of clumps forming high mass stars. However, previous studies have shown that there is no active massive star formation in this region. Recent measurements of near-infrared polarization infer that the magnetic field around M17 SWex is likely to be strong enough to support the cores against self-gravity. We therefore suggest that the magnetic field may prevent the cores from collapsing, causing the low-level of massive star formation in M17 SWex.