Testing the circumstellar disk hypothesis: A search for H2 outflow signatures from massive YSOs with linearly distributed methanol masers

Abstract

The results of a survey searching for outflows using near-infrared imaging is presented. Targets were chosen from a compiled list of massive young stellar objects (YSOs) associated with methanol masers in linear distributions. Presently, it is a widely held belief that these methanol masers are found in (and delineate) circumstellar accretion disks around massive stars. If this scenario is correct, one way to test the disk hypothesis is to search for outflows perpendicular to the methanol maser distributions. The main objective of the survey was to obtain wide-field near-infrared images of the sites of linearly distributed methanol masers using a narrow-band 2.12 micron filter. This filter is centered on the H2 v=1-0 S(1) line; a shock diagnostic that has been shown to successfully trace CO outflows from young stellar objects. Twenty-eight sources in total were imaged of which eighteen sources display H2 emission. Of these, only TWO sources showed emission found to be dominantly perpendicular to the methanol maser distribution. Surprisingly, the H2 emission in these fields is not distributed randomly, but instead the majority of sources are found to have H2 emission dominantly PARALLEL to their distribution of methanol masers. These results seriously question the hypothesis that methanol masers exist in circumstellar disks. The possibility that linearly distributed methanol masers are instead directly associated with outflows is discussed.