|28th of May 2018|
|Methanol masers with the ATCA|
Methanol (CH3OH) is often found in molecular clouds and around older
stars. In certain conditions, methanol masers (radio analogs of
lasers) are formed, stongly amplifying a spectral line of the methanol
molecule. Methanol masers which are collisionally excited are
referred to as Class I masers, whereas masers which are radiatively
excited are referred to as Class II masers.
McCarthy et al. have used the Australia Telescope Compact Array (ATCA) to observe a sample of 6.7-GHz class II methanol masers with an associated 95-GHz class I methanol maser, in order to make a detailed study of the relationship between the two methanol maser classes at arcsecond angular resolution. As these sources have previously been observed in the 36- and 44-GHz transitions, comparisons between several class I maser transitions were able to be made. A 3:1 flux density ratio is observed between the 95- and 44-GHz components, consistent with a number of previous lower angular resolution studies. The 95-GHz maser components appear to be preferentially located closer to the driving sources and this may indicate that this transition is more strongly inverted nearby to background continuum sources. The team find that in the majority of cases where both class I and class II methanol emission is observed, some component of the class I emission is associated with a likely outflow candidate.
The image shows a portion (approximately half an arcminute across) of the field image for G326.48+0.70. The background image is a multi-colour Spitzer infrared image. Four different symbols are overplotted: a square symbol represents a 6.7-GHz methanol maser, a cross represents a 36-GHz maser emission a plus sign represents a 44-GHz maser emission and a star symbol represents a 95-GHz maser emission. The solid red contours on the images represent 95-GHz continuum emission and the dashed contours represent the 50% and 90% levels of the ATLASGAL emission. The white circle represents the full width at half maximum (FWHM) of the primary beam centred on the pointing direction for the 95-GHz observations.
More details are given in the paper, published in Monthly Notices of the Royal Astronomical Society.