A Survey of Extended H$_2$ Emission from Massive YSOs

TL;DR

This survey investigates extended H₂ emission from massive young stellar objects to understand their accretion processes, revealing outflows and morphological features indicative of early star formation stages.

Contribution

It provides the first large-scale near-infrared imaging survey linking H₂ emission to outflow activity in massive YSOs, supporting accretion-based formation models.

Findings

Nearly half of the sources show extended H₂ emission.

21% of sources exhibit collimated outflow morphologies.

Extended H₂ emission is more common in radio-quiet, pre-UCHII phase objects.

Abstract

We present the results from a survey, designed to investigate the accretion process of massive young stellar objects (MYSOs) through near infrared narrow band imaging using the H$_2$ $\nu$=1-0 S(1) transition filter. A sample of 353 Massive Young Stellar Object (MYSO) candidates was selected from the Red MSX Source survey using photometric criteria at longer wavelengths (infrared and submillimeter) and chosen with positions throughout the Galactic Plane. Our survey was carried out at the SOAR Telescope in Chile and CFHT in Hawaii covering both hemispheres. The data reveal that extended H$_2$ emission is a good tracer of outflow activity, which is a signpost of accretion process on young massive stars. Almost half of the sample exhibit extended H$_2$ emission and 74 sources (21\%) have polar morphology, suggesting collimated outflows. The polar-like structures are more likely to appear on radio-quiet sources, indicating these structures occur during the pre-UCHII phase. We also found an important fraction of sources associated with fluorescent H$_2$ diffuse emission that could be due to a more evolved phase. The images also indicate only $\sim$23\% (80) of the sample is associated with extant (young) stellar clusters. These results support the scenario in which massive stars are formed by accretion disks, since the merging of low mass stars would not produce outflow structures.