A survey of extended H2 emission from massive YSOs

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 H2 ν=1–0 S(1) transition filter. A sample of 353 MYSO candidates was selected from the Red MSX Source survey using photometric criteria at longer wavelengths (infrared and submillimetre) and chosen with positions throughout the Galactic plane. Our survey was carried out at the Southern Astrophysical Research Telescope Telescope in Chile and Canada–France–Hawaii Telescope in Hawaii covering both hemispheres. The data reveal that extended H2 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 H2 emission and 74 sources (21 per cent) 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-UCH ii phase. We also found an important fraction of sources associated with fluorescent H2 diffuse emission that could be due to a more evolved phase. The images also indicate only ∼23 per cent (80) of the sample is associated with extant (young) stellar clusters. These results support the scenario in which massive stars are formed by accretion discs, since the merging of low-mass stars would not produce outflow structures.