Ionized Gas Towards Molecular Clumps: Physical Properties of Massive Star Forming Regions

TL;DR

This study investigates ionized gas in massive star-forming regions, discovering new HII regions, analyzing their association with molecular clumps, and estimating star formation efficiencies and mass relationships.

Contribution

It provides new observations of ionized gas in massive star-forming regions, including 20 newly discovered HII regions, and explores the relationship between clump mass and ionizing stars.

Findings

20 new HII regions discovered

Star formation efficiency averages 7%

Clump mass correlates with ionizing star mass

Abstract

We have conducted a search for ionized gas at 3.6 cm, using the Very Large Array, towards 31 Galactic intermediate- and high-mass clumps detected in previous millimeter continuum observations. In the 10 observed fields, 35 HII regions are identified, of which 20 are newly discovered. Many of the HII regions are multiply peaked indicating the presence of a cluster of massive stars. We find that the ionized gas tends to be associated towards the millimeter clumps; of the 31 millimeter clumps observed, 9 of these appear to be physically related to ionized gas, and a further 6 have ionized gas emission within 1'. For clumps with associated ionized gas, the combined mass of the ionizing massive stars is compared to the clump masses to provide an estimate of the instantaneous star formation efficiency. These values range from a few percent to 25%, and have an average of 7 +/- 8%. We also find a correlation between the clump mass and the mass of the ionizing massive stars within it, which is consistent with a power law. This result is comparable to the prediction of star formation by competitive accretion that a power law relationship exists between the mass of the most massive star in a cluster and the total mass of the remaining stars.