The Ionization of Accretion Flows in High Mass Star Formation: W51e2

TL;DR

This study presents high-resolution observations of ionized and molecular gas around W51e2, revealing a velocity gradient and bipolar outflow that support a phase in high-mass star formation where ionization begins while accretion continues.

Contribution

It provides new high-resolution radio and molecular line data showing the coexistence of ionized and accreting gas in high-mass star formation, highlighting an early ionization phase.

Findings

Velocity gradient in ionized gas > 500 km/s/pc

Detection of bipolar molecular outflow

Evidence of ongoing accretion during ionization phase

Abstract

Previous observations show that the hypercompact HII region W51e2 is surrounded by a massive molecular accretion flow centered on the HII region. New observations of the H53alpha radio recombination line made with the VLA at 0.45 arc second angular resolution show a velocity gradient in the ionized gas within the HII region of > 500 kms-1 pc-1 comparable to the velocity gradient seen in the molecular accretion flow. New CO line observations made with the SMA at arc second angular resolution detect a molecular bipolar outflow immediately around the W51e2 HII region and extending along the axis of rotation of the molecular flow. These observations are consistent with an evolutionary phase for high mass star formation in which a newly formed massive star first begins to ionize its surroundings including its own accretion flow.